Computational Study on the Effect of Axial Ligation Upon the Electronic Structure of Copper (II) Porphyrinate (CuTPPs = [5,10,15,20-tetrakis(N-methylpyridyl-4)porhinato]copper(II)tetratosylate)) - Electronic Structure with Different Axial Ligands
This document describes a computational study examining the effect of different axial ligands on the electronic structure of copper(II) porphyrinate complexes. Density functional theory was used to model complexes with nitrite, imidazole, phenol, and water ligands. The results show that axial ligands influence the copper spin density and delocalization in the complex. Ligands like nitrite and phenolate induce more spin delocalization compared to neutral ligands like water and phenol. The strength of axial bonding also varies, with ionic ligands forming stronger bonds than neutral ones involved in hydrogen bonding. This variation in electronic structure induced by different axial ligands could explain changes seen in experimental electron paramagnetic resonance spectra of related complexes.
Influence of the alkyl chain length of alkyltriazoles on the corrosion inhibi...Al Baha University
Abstract. Steel is an important material and has been widely used in today's industrial production. Using organic
corrosion inhibitors is an effective means to prevent steel from corrosion. Generally, the molecular structures of
inhibitors can have a major impact on their corrosion inhibition efficiency. In this work, the influence of alkyl chain
length of three alkyltriazoles on the corrosion inhibition of iron has been investigated by density functional based tight
binding (DFTB) approach. Several typical descriptors such as frontier molecular orbital, adsorption energy, density of
states have been discussed in detail. Our findings will contribute to the understanding of the inhibition mechanism and
the designing of novel corrosion inhibitors.
Iron, cobalt and Nickel -ligand bonding in metallocene: Differentiation betwe...AI Publications
The electronic structure and geometry optimization of ferrocene, cobaltocene and nickelocene molecules using DFT/B3LYP with the basis set of 6-31G (d) calculations. The Eigen values, Eigen vector and population analysis of the molecules show that the first 13 molecular orbitals in ferrocene, 12 in cobaltocene and 14 in nickelocene have contribution from 2pzorbitals of carbon of (C5H5)− and4s,4pand 3dorbitals of iron, cobalt or nickel, respectively. We found that the extents of involvement of metal orbitals in the three cases are different. In ferrocene the maximum involvement out of 4s and 4porbitals in the order 4pz >4py >4s > 4pxand out of 3d orbitals the order of involvement is 3dyz >3dxz >3d2z>3dx2−y2>3dxy. The involvement of corresponding orbital in cobaltocene with respect to the 4sand 4porbitals is in the order of 4s >4pz >4py >4pxand in 3d orbitals the order is 3dx2−y2>3dxz >3d2z>3dx2−y2 and in the nickelocene molecule it is 4py >4p>4s >4pz and in 3d orbitals the order is 3dyz >3dx2−y2>3dxy >3dxz >3d2z. The total involvement of 3d, 4s and 4porbitals of metal and 2pz orbitals of the ten carbon atoms of both ligands of (C5H5) −in ferrocene, cobaltocene and nickelocene respectively are 42.2528, 40.2388 and 38.3776
A detailed study of Transition Metal Complexes of a Schiff base with its Phys...Abhishek Ghara
The many activities of metal ions in biology have stimulated the development of metal based therapeutics. It has been found that biologically active compounds become more effective and bacteriostatic upon chelation with metal ions also the biological activity of many drugs has been shown to be enhanced on complexing with metal ions, hence promoting their use in Pharmacology. The present work deals with the synthesis of metal complexes derived from a novel Schiff base drug synthesized from urea and salicylaldehyde and its physico-chemical analysis to find out ligand- metal ratio of this complex in solution. For the structure elucidation of these complexes “Monovariation method (Mole ratio method/ Yoe-Jones Method)” has been used to ascertain the ligand-metal ratio in the complex. The stability constant of the formed complex was calculated by molar conductance measurement using Modified Job’s method (Method of Continuous Variations). The analysis has been carried out using conductometry. To confirm metal-ligand ratio, conductometric titrations were carried out at room temperature using analytical grade metal salts. Titrations were carried out with “systronics conductivity-meter” using dip type conductivity cell having cell constant 1 at room temperature.
This document summarizes the synthesis and study of transition metal complexes of benzaldimino-1,3,4-thiadiazole-2-thiol (BTT). The author synthesized the ligand BTT and its copper, nickel, cobalt, and zinc complexes. The complexes were characterized using infrared spectroscopy, electronic spectroscopy, ESR, cyclic voltammetry, NMR, and magnetic susceptibility measurements. Spectroscopic data indicated the ligand behaves as a bidentate ligand, forming octahedral complexes with the metals. The author thanks advisors and colleagues and concludes the spectral studies support an octahedral geometry for the complexes.
The document summarizes four new heterometallic molecular aggregates containing cobalt and lanthanide metals. Compounds 1 and 2 have the formula [(CoII)3(CoIII)2Ln3(μ3-OH)5(O2CtBu)12(L)2]·2H2O and feature distorted cubane cores, while compounds 3 and 4 have the formula [(CoIII)3Ln3(μ3-OH)4(O2CtBu)6(L)3](NO3)2·2CH3CN·2H2O and display hemicubane-like metallic cores. Magnetic studies show significant magnetic entropy changes for 1 and 3, and single molecule magnetic
This document describes a one-pot synthesis of wurtzite and chalcopyrite CuFeS2 nanoparticles using a copper thiourea complex and different iron salts. Reactng the copper complex with iron(II) sulfate produces wurtzite CuFeS2, while reacting with iron(III) chloride produces chalcopyrite CuFeS2. Both phases were characterized using techniques like XRD, SEM, TEM, Raman spectroscopy, UV-Vis spectroscopy, and PL spectroscopy. This synthesis allows control over the crystal structure produced and provides phases with potential for tuning optoelectronic and magnetic properties.
Synthesis, Characterization and antimicrobial activity of some novel sulfacet...iosrjce
IOSR Journal of Applied Chemistry (IOSR-JAC) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of applied chemistry and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in Chemical Science. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
The document summarizes the synthesis and characterization of a novel square-grid complex with the formula [Cu16L18](dmf)3 (1). The complex was formed through self-assembly of a 2,6-pyridinedicarbaldehyde bis(hydrazone) ligand (H4L1) and Cu2+ salt. X-ray crystallography revealed a [4x4] square grid structure consisting of 16 Cu2+ ions in a mixed coordination environment bridged by the ligand. Magnetic measurements showed both ferro- and antiferromagnetic spin exchanges occurring, with antiferromagnetic coupling dominating at low temperatures.
Influence of the alkyl chain length of alkyltriazoles on the corrosion inhibi...Al Baha University
Abstract. Steel is an important material and has been widely used in today's industrial production. Using organic
corrosion inhibitors is an effective means to prevent steel from corrosion. Generally, the molecular structures of
inhibitors can have a major impact on their corrosion inhibition efficiency. In this work, the influence of alkyl chain
length of three alkyltriazoles on the corrosion inhibition of iron has been investigated by density functional based tight
binding (DFTB) approach. Several typical descriptors such as frontier molecular orbital, adsorption energy, density of
states have been discussed in detail. Our findings will contribute to the understanding of the inhibition mechanism and
the designing of novel corrosion inhibitors.
Iron, cobalt and Nickel -ligand bonding in metallocene: Differentiation betwe...AI Publications
The electronic structure and geometry optimization of ferrocene, cobaltocene and nickelocene molecules using DFT/B3LYP with the basis set of 6-31G (d) calculations. The Eigen values, Eigen vector and population analysis of the molecules show that the first 13 molecular orbitals in ferrocene, 12 in cobaltocene and 14 in nickelocene have contribution from 2pzorbitals of carbon of (C5H5)− and4s,4pand 3dorbitals of iron, cobalt or nickel, respectively. We found that the extents of involvement of metal orbitals in the three cases are different. In ferrocene the maximum involvement out of 4s and 4porbitals in the order 4pz >4py >4s > 4pxand out of 3d orbitals the order of involvement is 3dyz >3dxz >3d2z>3dx2−y2>3dxy. The involvement of corresponding orbital in cobaltocene with respect to the 4sand 4porbitals is in the order of 4s >4pz >4py >4pxand in 3d orbitals the order is 3dx2−y2>3dxz >3d2z>3dx2−y2 and in the nickelocene molecule it is 4py >4p>4s >4pz and in 3d orbitals the order is 3dyz >3dx2−y2>3dxy >3dxz >3d2z. The total involvement of 3d, 4s and 4porbitals of metal and 2pz orbitals of the ten carbon atoms of both ligands of (C5H5) −in ferrocene, cobaltocene and nickelocene respectively are 42.2528, 40.2388 and 38.3776
A detailed study of Transition Metal Complexes of a Schiff base with its Phys...Abhishek Ghara
The many activities of metal ions in biology have stimulated the development of metal based therapeutics. It has been found that biologically active compounds become more effective and bacteriostatic upon chelation with metal ions also the biological activity of many drugs has been shown to be enhanced on complexing with metal ions, hence promoting their use in Pharmacology. The present work deals with the synthesis of metal complexes derived from a novel Schiff base drug synthesized from urea and salicylaldehyde and its physico-chemical analysis to find out ligand- metal ratio of this complex in solution. For the structure elucidation of these complexes “Monovariation method (Mole ratio method/ Yoe-Jones Method)” has been used to ascertain the ligand-metal ratio in the complex. The stability constant of the formed complex was calculated by molar conductance measurement using Modified Job’s method (Method of Continuous Variations). The analysis has been carried out using conductometry. To confirm metal-ligand ratio, conductometric titrations were carried out at room temperature using analytical grade metal salts. Titrations were carried out with “systronics conductivity-meter” using dip type conductivity cell having cell constant 1 at room temperature.
This document summarizes the synthesis and study of transition metal complexes of benzaldimino-1,3,4-thiadiazole-2-thiol (BTT). The author synthesized the ligand BTT and its copper, nickel, cobalt, and zinc complexes. The complexes were characterized using infrared spectroscopy, electronic spectroscopy, ESR, cyclic voltammetry, NMR, and magnetic susceptibility measurements. Spectroscopic data indicated the ligand behaves as a bidentate ligand, forming octahedral complexes with the metals. The author thanks advisors and colleagues and concludes the spectral studies support an octahedral geometry for the complexes.
The document summarizes four new heterometallic molecular aggregates containing cobalt and lanthanide metals. Compounds 1 and 2 have the formula [(CoII)3(CoIII)2Ln3(μ3-OH)5(O2CtBu)12(L)2]·2H2O and feature distorted cubane cores, while compounds 3 and 4 have the formula [(CoIII)3Ln3(μ3-OH)4(O2CtBu)6(L)3](NO3)2·2CH3CN·2H2O and display hemicubane-like metallic cores. Magnetic studies show significant magnetic entropy changes for 1 and 3, and single molecule magnetic
This document describes a one-pot synthesis of wurtzite and chalcopyrite CuFeS2 nanoparticles using a copper thiourea complex and different iron salts. Reactng the copper complex with iron(II) sulfate produces wurtzite CuFeS2, while reacting with iron(III) chloride produces chalcopyrite CuFeS2. Both phases were characterized using techniques like XRD, SEM, TEM, Raman spectroscopy, UV-Vis spectroscopy, and PL spectroscopy. This synthesis allows control over the crystal structure produced and provides phases with potential for tuning optoelectronic and magnetic properties.
Synthesis, Characterization and antimicrobial activity of some novel sulfacet...iosrjce
IOSR Journal of Applied Chemistry (IOSR-JAC) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of applied chemistry and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in Chemical Science. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
The document summarizes the synthesis and characterization of a novel square-grid complex with the formula [Cu16L18](dmf)3 (1). The complex was formed through self-assembly of a 2,6-pyridinedicarbaldehyde bis(hydrazone) ligand (H4L1) and Cu2+ salt. X-ray crystallography revealed a [4x4] square grid structure consisting of 16 Cu2+ ions in a mixed coordination environment bridged by the ligand. Magnetic measurements showed both ferro- and antiferromagnetic spin exchanges occurring, with antiferromagnetic coupling dominating at low temperatures.
The document summarizes research on synthesizing new inorganic complexes by reacting iron carbonyl dianions with an indium tris(3,5-dimethyl)-1-pyrazolylborate moiety. Specifically, reacting [HB(3,5-Me2-pz)3]InCl2·THF with [Fe(C2H4(NH2)2)3][Fe2(CO)8] or [Fe(C2H4(NH2)2)3][Fe3(CO)11] yielded new complexes as shown by IR and NMR spectroscopy, which indicate new indium-iron bonds and coordination of the pyrazolylborate ligand to the
1. The document describes the synthesis and characterization of novel Schiff base ligands and their transition metal complexes.
2. Several heterocyclic aldehydes and aniline derivatives were synthesized and used to prepare Schiff bases. These include Schiff bases derived from 4-methylumbelliferone and N-methylpropane-1,3-diamine.
3. The Schiff bases were characterized using analytical techniques like NMR, MS and IR spectroscopy. They were then used to prepare transition metal complexes which will be explored for potential biological activities.
This document describes the room temperature synthesis of copper sulfide (Cu9S5), copper selenide (CuSe), lead sulfide (PbS), and lead selenide (PbSe) by reacting the elemental powders in 2-mercaptoethanol solvent for 24 hours. Characterization by powder X-ray diffraction and Raman spectroscopy showed the products were highly crystalline. Reactions in ethylene glycol also yielded copper sulfide and lead sulfide but reactions in dimercaptoethane did not yield metal chalcogenides. This solvent-mediated room temperature synthesis provides a simple method for producing these metal chalcogenide materials.
1. A 2D coordination polymer was synthesized using cobalt trimers and the flexible ligand cis,cis-cyclohexane-1,3,5-tricarboxylate.
2. Single crystal X-ray diffraction shows the complex forms a 2D framework with channels and contains trinuclear cobalt secondary building units linked by the ligand.
3. Magnetic characterization reveals spin-canting ferromagnetic behavior at low temperatures based on AC susceptibility measurements. Gas adsorption experiments also show selectivity for CO2 over N2.
Superconductivity in Al-substituted Ba8Si46 clathratesYang Li
There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed
that Ba8Si42Al4 is superconductive with transition temperature at TC=5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x=6 sample Ba8Si40Al6, the superconducting transition was observed down to TC=4.7K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC=8K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a
decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated
by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensiveunderstanding of the doping effect on superconductivity of clathrates.
This document summarizes the synthesis and characterization of new Schiff base ligands and their metal complexes. It describes the synthesis of five Schiff base ligands derived from substituted benzaldehydes and anilines using the reflux method. Copper and nickel complexes were formed from two of the ligands. The ligands and complexes were characterized using infrared spectroscopy, which showed shifts in the C=N and C-O peaks upon complexation. The research aims to synthesize new Schiff bases and their Cu2+ and Ni2+ complexes and characterize them using IR spectroscopy to determine the coordination sites.
The document discusses using boron-doped carbon nanotubes as a catalyst for oxygen reduction in proton exchange membrane fuel cells. Density functional theory and Nudged Elastic Band calculations were used to study oxygen dissociation across a boron-doped (5,5) single-walled carbon nanotube. The most favorable reaction path was determined to have an activation barrier of 0.5 eV, lower than previous studies using a single boron atom. This is likely due to cooperative effects of having three boron atoms and electron transfer from boron to oxygen. While the 0.5 eV barrier is still relatively high, solvent effects in real systems could further reduce it. Boron-doped carbon nanotubes
Crystal Structure, Topological and Hirshfeld Surface Analysis of a Zn(II) Zwi...Awad Albalwi
Abstract: A mononuclear Zn(II) complex of (Zn(H2L) (CH3OH) Cl2
) (1) has been synthesized by using
a nonlinear optically active Zwitterionic Schiff base which is 4-((2-hydroxy-3-methoxybenzylidene)
amino) benzoic acid (H2L). Complex 1 has been structurally analyzed by FTIR and UV spectroscopy,
TGA, Powder-XRD and single crystal X-ray diffraction. X-Ray crystallographic studies revealed Zn(II)
complex crystallizes in a P21/c space group and exists in a distorted trigonal bipyramidal geometry
(τ = 0.68).
This document summarizes research on synthesizing copper sulfide compounds Cu1.8S and CuS from copper-thiourea precursors containing different counteranions (Cl-, NO3-, SO42-). When reacted in ethylene glycol, [Cu4(tu)9](NO3)4 always yielded CuS regardless of conditions. [Cu(tu)3]Cl yielded only Cu1.8S in air or argon, but a mixture of Cu1.8S and CuS under solvothermal conditions. [Cu2(tu)6]SO4 produced a mixture of CuS and Cu1.8S under all conditions tested. The counteranion's oxidizing power
The document describes the synthesis of Schiff base ligands derived from citral and valine and their complexes with Cu(II), Ni(II), and Co(II). The structures of the complexes were characterized using IR, UV-vis, and magnetic susceptibility measurements. The Cu(II) and Ni(II) complexes were proposed to have distorted octahedral geometry while the Co(II) complex had square-based pyramidal geometry. Antimicrobial testing showed that the metal complexes had higher activity than the free ligand, with the Co(II) complex being most active.
Synthesis, Spectroscopic Studies and Antibacterial Activity of Novel Schiff B...IRJET Journal
The document describes the synthesis and characterization of novel Schiff base metal complexes derived from condensation of 5-bromosalicylaldehyde, 4,5-dichloro-o-phenylenediamine, and pentane-2,4-dione. Specifically, copper(II), nickel(II), and oxovanadium(IV) complexes were synthesized and characterized using analytical, spectral, electrochemical, and antimicrobial methods. The complexes were found to have general formula [M(L)]X where M is the metal and L is the tetradentate Schiff base ligand. Spectroscopic data indicated the ligand coordinates through the hydroxyl oxygen and azomethine nitrogen. The metal complexes
Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Vale...IOSR Journals
This document summarizes an ab initio study of the electronic band structure and phonon dispersion of silver oxide (AgO) using density functional theory calculations. The LDA+U method predicted AgO to be a semimetal, while the Hartree-Fock calculation predicted a semiconductor with an indirect bandgap of 1.53 eV, consistent with experiments. Phonon calculations showed small splitting between longitudinal and transverse optical modes for higher oxygen vibrations, explaining why Raman spectroscopy could not observe these modes. The study provides insights into the electronic properties and vibrational behavior of the mixed valence silver oxide.
The IOSR Journal of Pharmacy (IOSRPHR) is an open access online & offline peer reviewed international journal, which publishes innovative research papers, reviews, mini-reviews, short communications and notes dealing with Pharmaceutical Sciences( Pharmaceutical Technology, Pharmaceutics, Biopharmaceutics, Pharmacokinetics, Pharmaceutical/Medicinal Chemistry, Computational Chemistry and Molecular Drug Design, Pharmacognosy & Phytochemistry, Pharmacology, Pharmaceutical Analysis, Pharmacy Practice, Clinical and Hospital Pharmacy, Cell Biology, Genomics and Proteomics, Pharmacogenomics, Bioinformatics and Biotechnology of Pharmaceutical Interest........more details on Aim & Scope).
All manuscripts are subject to rapid peer review. Those of high quality (not previously published and not under consideration for publication in another journal) will be published without delay.
This Journal publishes original research work that contributes significantly to further the scientific knowledge in pharmacy.
Synthesis and characterization of mixed ligand complexes of some metals with ...Taghreed Al-Noor
This document summarizes the synthesis and characterization of mixed ligand metal complexes containing nicotinamide and L-phenylalanine. The complexes were synthesized and analyzed using various techniques such as melting point, solubility, molar conductivity, UV-Vis and FT-IR spectroscopy. The complexes had the general formula [M(NA)2(phe)]Cl, where M is a divalent metal ion such as Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II). The study showed that L-phenylalanine acted as a bidentate ligand through its carboxylate and amine groups, while nicotinamide coordinated as
Studies On The Cobalt(II) And Copper(II) Complexes Of 2,5-Substituted 1,3,4-T...IOSR Journals
1. New metal complexes of Co(II) and Cu(II) were synthesized by reacting solutions of the metal salts with 2,5-substituted 1,3,4-triazole ligands in an alcoholic medium.
2. The complexes were characterized through techniques such as elemental analysis, magnetic susceptibility, molar conductance, and IR spectroscopy.
3. Based on analytical data and characterization, the complexes were determined to have a 1:2 metal to ligand ratio and the ligand was found to act as a bidentate ligand coordinating through nitrogen atoms in the ring.
Spectroscopic characterization and biological activityMahmoud Abdulla
This document describes the spectroscopic characterization and biological activity of metal complexes of a Schiff base ligand. Specifically, it discusses:
1) The synthesis of the Schiff base ligand from pyrrole-2-carboxaldehyde and 2-aminophenol and its subsequent complexation with Zn(II), Cd(II), Sn(II), and Pb(II) metals.
2) Spectroscopic studies of the complexes including IR, 1H NMR, electronic, and mass spectra that indicate coordination through the azomethine nitrogen and deprotonated phenolic oxygen.
3) Thermal decomposition studies using TG-DTA that show endothermic and exothermic transitions.
4)
Synthesis and characterization of complexes of schiff base [1, 2 diphenyl -...Alexander Decker
This document describes the synthesis and characterization of a Schiff base ligand and its complexes with various metal ions. The ligand (HL) was prepared in two steps by reacting 3-aminoacetophenone with hydrazine monohydrate to form an intermediate, which was then reacted with salicylaldehyde. The ligand was characterized using various techniques. The metal complexes were prepared by reacting the ligand with metal chlorides in a 1:1 molar ratio. The complexes were characterized using techniques such as elemental analysis, conductivity, IR spectroscopy, UV-Vis spectroscopy, and magnetic susceptibility measurements. Based on the data, the complexes were found to have tetrahedral geometry except for the nickel complex which was square planar.
This document summarizes the synthesis of zincblende CuInS2 and iron-substituted CuInS2 by reacting colloidal suspensions of binary Cu-S and In-S in ethyleneglycol. Characterization with techniques such as XRD, TEM, UV-Vis and Raman spectroscopy confirmed the formation of phase pure zincblende CuInS2. Following this, quaternary Cu-In-Fe-S with zincblende structure was also synthesized by including iron in the reaction. While zincblende CuInS2 degraded methylene blue dye under visible light, the iron-substituted sample did not show appreciable degradation.
This summary provides the key details from the document in 3 sentences:
The document reports on a study of chromium-catalyzed ethylene oligomerization using bis(benzimidazolemethyl)amine (BIMA) ligands. It finds that N-alkyl-substituted BIMA ligands produce extremely high catalyst activities (>100,000 g mmol-1 h-1 bar-1) and yield alternating distributions of linear α-olefins. The alternating distributions can be explained by a metallacyclic mechanism in which both single and double ethylene insertions into the metallacycle are possible.
This study investigates the corrosion inhibition of iron by six mono-azo dye derivatives (MAD_1-6) in 2M HNO3 and 2M NaOH solutions using experimental and computational methods. Gravimetric, thermometric, UV-Vis spectrophotometric, and electrochemical polarization techniques were used to determine inhibition efficiencies experimentally. Density functional theory calculations and molecular dynamics simulations were performed to calculate quantum chemical parameters and binding energies on the Fe(110) surface. Theoretical data agreed well with experimental inhibition efficiencies, with MAD_1 and MAD_6 showing the best inhibition in acidic and alkaline solutions, respectively.
This document presents a theoretical study examining the effects of central metal ions (Cd2+, Hg2+, Pt2+) and substituent groups (F, I, NO2, NH2, CH3, H) on the properties of metalloporphyrin complexes for use as semiconductor materials. Density functional theory calculations were used to analyze the electronic structure, density of states, and UV-Vis absorption spectra of the complexes. The results showed that electron-donating substituents and central ions from Hg to Cd to Pt decreased the bandgap and shifted absorption peaks to longer wavelengths, indicating better semiconductor performance for light absorption. NH2 substituents gave the best results with the smallest bandgap and longest absorption peak.
The document discusses molecular orbital theory and its application to transition metal complexes. It describes how atomic orbitals of matching symmetry combine to form molecular orbitals, with equal numbers of bonding and antibonding orbitals. Electrons fill the molecular orbitals starting with the lowest energy orbitals. Ligand interactions such as π-accepting and π-donating affect the splitting of orbitals and influence the metal's oxidation state.
The document summarizes research on synthesizing new inorganic complexes by reacting iron carbonyl dianions with an indium tris(3,5-dimethyl)-1-pyrazolylborate moiety. Specifically, reacting [HB(3,5-Me2-pz)3]InCl2·THF with [Fe(C2H4(NH2)2)3][Fe2(CO)8] or [Fe(C2H4(NH2)2)3][Fe3(CO)11] yielded new complexes as shown by IR and NMR spectroscopy, which indicate new indium-iron bonds and coordination of the pyrazolylborate ligand to the
1. The document describes the synthesis and characterization of novel Schiff base ligands and their transition metal complexes.
2. Several heterocyclic aldehydes and aniline derivatives were synthesized and used to prepare Schiff bases. These include Schiff bases derived from 4-methylumbelliferone and N-methylpropane-1,3-diamine.
3. The Schiff bases were characterized using analytical techniques like NMR, MS and IR spectroscopy. They were then used to prepare transition metal complexes which will be explored for potential biological activities.
This document describes the room temperature synthesis of copper sulfide (Cu9S5), copper selenide (CuSe), lead sulfide (PbS), and lead selenide (PbSe) by reacting the elemental powders in 2-mercaptoethanol solvent for 24 hours. Characterization by powder X-ray diffraction and Raman spectroscopy showed the products were highly crystalline. Reactions in ethylene glycol also yielded copper sulfide and lead sulfide but reactions in dimercaptoethane did not yield metal chalcogenides. This solvent-mediated room temperature synthesis provides a simple method for producing these metal chalcogenide materials.
1. A 2D coordination polymer was synthesized using cobalt trimers and the flexible ligand cis,cis-cyclohexane-1,3,5-tricarboxylate.
2. Single crystal X-ray diffraction shows the complex forms a 2D framework with channels and contains trinuclear cobalt secondary building units linked by the ligand.
3. Magnetic characterization reveals spin-canting ferromagnetic behavior at low temperatures based on AC susceptibility measurements. Gas adsorption experiments also show selectivity for CO2 over N2.
Superconductivity in Al-substituted Ba8Si46 clathratesYang Li
There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed
that Ba8Si42Al4 is superconductive with transition temperature at TC=5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x=6 sample Ba8Si40Al6, the superconducting transition was observed down to TC=4.7K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC=8K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a
decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated
by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensiveunderstanding of the doping effect on superconductivity of clathrates.
This document summarizes the synthesis and characterization of new Schiff base ligands and their metal complexes. It describes the synthesis of five Schiff base ligands derived from substituted benzaldehydes and anilines using the reflux method. Copper and nickel complexes were formed from two of the ligands. The ligands and complexes were characterized using infrared spectroscopy, which showed shifts in the C=N and C-O peaks upon complexation. The research aims to synthesize new Schiff bases and their Cu2+ and Ni2+ complexes and characterize them using IR spectroscopy to determine the coordination sites.
The document discusses using boron-doped carbon nanotubes as a catalyst for oxygen reduction in proton exchange membrane fuel cells. Density functional theory and Nudged Elastic Band calculations were used to study oxygen dissociation across a boron-doped (5,5) single-walled carbon nanotube. The most favorable reaction path was determined to have an activation barrier of 0.5 eV, lower than previous studies using a single boron atom. This is likely due to cooperative effects of having three boron atoms and electron transfer from boron to oxygen. While the 0.5 eV barrier is still relatively high, solvent effects in real systems could further reduce it. Boron-doped carbon nanotubes
Crystal Structure, Topological and Hirshfeld Surface Analysis of a Zn(II) Zwi...Awad Albalwi
Abstract: A mononuclear Zn(II) complex of (Zn(H2L) (CH3OH) Cl2
) (1) has been synthesized by using
a nonlinear optically active Zwitterionic Schiff base which is 4-((2-hydroxy-3-methoxybenzylidene)
amino) benzoic acid (H2L). Complex 1 has been structurally analyzed by FTIR and UV spectroscopy,
TGA, Powder-XRD and single crystal X-ray diffraction. X-Ray crystallographic studies revealed Zn(II)
complex crystallizes in a P21/c space group and exists in a distorted trigonal bipyramidal geometry
(τ = 0.68).
This document summarizes research on synthesizing copper sulfide compounds Cu1.8S and CuS from copper-thiourea precursors containing different counteranions (Cl-, NO3-, SO42-). When reacted in ethylene glycol, [Cu4(tu)9](NO3)4 always yielded CuS regardless of conditions. [Cu(tu)3]Cl yielded only Cu1.8S in air or argon, but a mixture of Cu1.8S and CuS under solvothermal conditions. [Cu2(tu)6]SO4 produced a mixture of CuS and Cu1.8S under all conditions tested. The counteranion's oxidizing power
The document describes the synthesis of Schiff base ligands derived from citral and valine and their complexes with Cu(II), Ni(II), and Co(II). The structures of the complexes were characterized using IR, UV-vis, and magnetic susceptibility measurements. The Cu(II) and Ni(II) complexes were proposed to have distorted octahedral geometry while the Co(II) complex had square-based pyramidal geometry. Antimicrobial testing showed that the metal complexes had higher activity than the free ligand, with the Co(II) complex being most active.
Synthesis, Spectroscopic Studies and Antibacterial Activity of Novel Schiff B...IRJET Journal
The document describes the synthesis and characterization of novel Schiff base metal complexes derived from condensation of 5-bromosalicylaldehyde, 4,5-dichloro-o-phenylenediamine, and pentane-2,4-dione. Specifically, copper(II), nickel(II), and oxovanadium(IV) complexes were synthesized and characterized using analytical, spectral, electrochemical, and antimicrobial methods. The complexes were found to have general formula [M(L)]X where M is the metal and L is the tetradentate Schiff base ligand. Spectroscopic data indicated the ligand coordinates through the hydroxyl oxygen and azomethine nitrogen. The metal complexes
Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Vale...IOSR Journals
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Computational Study on the Effect of Axial Ligation Upon the Electronic Structure of Copper (II) Porphyrinate (CuTPPs = [5,10,15,20-tetrakis(N-methylpyridyl-4)porhinato]copper(II)tetratosylate)) - Electronic Structure with Different Axial Ligands
1. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
405
Computational Study on the Effect of Axial Ligation Upon the
Electronic Structure of Copper (II) Porphyrinate
(CuTPPs = [5,10,15,20-tetrakis(N-methylpyridyl-4)porhinato]copper(II)tetratosylate))
- Electronic Structure with Different Axial Ligands
Roxana-Viruca Ţolan, Alexandru Lupan*, Radu Silaghi-Dumitrescu
Department of Chemistry, Faculty of Chemistry and Chemical Engineering,”Babes-Bolyai” University, Arany
Janos Str. no. 11, RO-400028, Cluj Napoca, Romania.
alupan@chem.ubbcluj.ro*
(Received on 5th
December 2013, accepted in revised form 22nd
December 2015)
Summary: Copper porphyrins are generally known to show a less diverse reactivity as compared
to their iron counterparts, both redox-wise and in terms of axial ligation. Reported here are density
functional theory (DFT) results on models of copper (II)-porphyrins (models of [5,10,15,20-
tetrakis(N-methylpyridyl-4)porhinato]copper(II)tetratosylate) with a set of axial ligands – nitrite
(both the nitrogen-bound isomer and the oxygen-bound isomer, i.e., nitro and nitrito), imidazole,
two forms of phenol (neutral and anionic), and water - related to an unexpected range of electronic
structures detectable in electron paramagnetic resonance (EPR) spectra of a water-soluble copper
porphyrin with water, nitrite, imidazole, dithionite, 2,2'-azino-bis(3-ethylbenzthiazoline-6-
sulphonic acid) (ABTS) and guaiacol. Computed spin densities and atomic charges reveal various
degrees of influence of the axial ligands on the Cu-porphyrin electronic structure, which may be
related to the notably different changes induced by each ligand (imidazole, nitrite, guaiacol and
ABTS) on the EPR superhyperfine splitting, but with an unexpectedly strong dependence on
choice of the computational methodology. Thus, at the B3LYP/6-31G** level the copper spin
densities are predicted to range from 0.69 to 0.73 depending on the axial ligand, this contribution
being located on the dx2-y2 orbital in a range from 65% to 100%. BP86/DN** results tend to favor a
distinctly larger spread of these values.
Keywords: copper, porphyrin, DFT, spin, EPR, molecular orbital.
Introduction
Copper porphyrins show a less diverse
reactivity as compared to iron porphyrins, both
redox-wise and in terms of axial ligation. Oxidation
reactions of the Cu(II)-porphyrin complexes typically
take place at the porphyrin ligand while the central
copper ion remains in the oxidation state of +2; in
contrast iron, manganese or cobalt can lead to formal
oxidation states as high as +5 [1, 2].
Copper(II) porphyrins can bind to DNA due
to the absence of a fifth axial ligand and are capable
of both binding and intercalation exhibiting
preference for GC (guanine-cytosine) base pairs [3].
However, there is little direct evidence for axial
ligand exchange reactions at the copper in
porphyrins. Another copper-porphyrin complex
(sodium-copper chlorophyllin) has been shown to act
as an inhibitor and also as a promoter of DNA-
damage induction by a variety of mutagens [4].
The water-soluble copper porphyrinate,
copper (II) porphyrinate (CuTPPs = [5,10,15,20-
tetrakis(N-methylpyridyl-4)porhinato]copper(II)
tetratosylate)), was previously examined by UV-Vis
and electron paramagnetic (EPR) spectroscopy for its
ability to engage in a number of reactions involving
either axial ligation to the copper or possible redox
cycling, with ligands and potential redox partners
such as nitrite, imidazole, dithionite, 2,2'-azino-bis(3-
ethylbenzthiazoline-6-sulphonic acid) (ABTS) and
guaiacol [5]. Almost non-detectable changes in the
UV-vis spectra of CuTPPs were noted, in contrast to
an unexpected range of electronic structures clearly
detectable in the EPR spectra [5]. The superhyperfine
coupling seen in the CuTPPs spectra with some of the
ligands was distinctly larger than anything previously
reported for iron porphyrins or related systems [6],
and was reminiscent of previously noted
manifestations in copper porphyrinate complexes [7].
The present work aims to investigate the electronic
structure basis of these changes in EPR spectra,
employing theoretical methods. Indeed,
computational methods, especially density functional
theory and to some extent semiempirical ones,
generally provide useful insight into transition metal
complexes, including porphyrinates [8].
Experimental
Density functional theory (DFT)
calculations were carried out using the Gaussian 09
[22], Spartan 5 [23] and Spartan '06 [24] software
ANALYTICAL AND INORGAIC
*
To whom all correspondence should be addressed.
2. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
406
packages. The Results section discusses Gaussian 09
results, unless otherwise specified.
All the structures considered in the study
(Fig. 1) were constructed using the graphical
interface of Spartan '06 program. Geometry
optimizations and frequencies analysis were carried
out using the gradient corrected hybrid density
functional B3LYP [25-28] in conjugation with 6-
31G** basis set in Gaussian 09 and in Spartan '06.
The choice of B3LYP/6-31G** is based on the fact
that it has been demonstrated that B3LYP is excellent
in modeling this type of molecules [29-32]. Default
convergence criteria were employed in each software
package.
Single-point calculations of structures 1-7 in
water were also performed using B3LYP/6-31G** on
gas-phase-optimized geometries, using the COSMO
model as implemented in Gaussian09 (CPCM) [33].
For molecules 1-7 a natural bond orbitals analysis
(NBO) [34] was also performed in Gaussian. Ligand
binding energies were calculated with formula ΔE =
[E(model) - E(model 1) - E(ligand)], where E is the
each model energy calculated with Spartan '06.
Results and Discussion
Reported here are computational data on
copper (II) porphyrinate (CuTPPs) complexes, in the
context of the previously discussed [5] unexpected
range of electronic structures detectable in EPR
spectra. In the experimental measurements the axial
ligands were nitrite, imidazole, dithionite, ABTS and
guaiacol (Fig. 1). The axial ligands employed in our
calculations are therefore nitrite, imidazole, and two
forms of phenol (neutral and anionic) . The latter is
used as a model for guaiacol and/or ABTS. Also
examined was a water ligand, since the EPR spectra
were recorded in water. Modeling binding of
dithionite to the copper was not attempted, due to the
fact that multiple binding modes are possible not only
for dithionite but also for its several possible
decomposition products (e.g. SO2
-
, S2O3
2-
, SO3
2-
).
The optimized geometries for models 1-7 are shown
in Fig. 2, with energies reported in Table-1.
Fig. 1: Models employed in the present study.
3. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
407
Table-1: Calculated energy and ligand binding
energies. ΔE=[E(model)-E(model 1)-E(ligand)].
No. E (hartree) ΔE(kcal/mol)
1 -2628.770282 0
2 -2705.200431 -6.5
3 -2833.925829 -22.0
4 -2843.930806 -25.0
5 -2935.684879 -13.9
6 -2936.256475 -4.8
7 -2855.002833 -5.7
As seen in Fig. 2, structure 1 remains
entirely planar as expected. In the other structures,
the copper is slightly displaced out of the porphyrin
plane, depending on the strength of the axial bonds;
these displacements are, however, generally very
small, cf. Table-2: between 0.02 and 0.06 Å for the
weakly-binding water and phenol, and between 0.22
and 0.45 Å for the more properly bound nitrite,
phenolate and imidazole – with the maximum
distance seen for the O-nitrite adduct. For the latter
case, the distance between the metal and the plane
defined by the macrocycle nitrogens is ~double
compared to what is computed for a model where the
Cu(II) was replaced with Fe(III) or Fe(II) (0.17 Å, cf.
geometries reported in [9] and similar ones in [10,
11] – arguably because of a larger radius of the
copper compared to iron (van der Waals radius of
1.57 Å compared to 1.31 Å, respectively).
In structure 2 the water ligand forms two
hydrogen bonds with the nitrogen atoms from the
porphyrin (N---H distances of ~2.5 Å cf. Table-2,
which is shorter than the sum of van der Waals radii
of nitrogen and hydrogen, of 2.75 Å). In structure 6
(the phenol adduct) the same happens with the
hydrogen atom from protonated phenol, with the 2.16
Å N—H distance (cf. Table-2) indicating a hydrogen
bond stronger than those established by water. The
hydrogen bonds established in models 2 and 6 are
paralleled by the fact that the bond lengths between
Cu and O are particularly elongated; in fact, with
2.71 and 3.17 Å, these Cu-O distances are longer
than the N---H hydrogen bonds and, in the case of the
phenol adducts, even longer than the sum of van der
Waals radii of copper and oxygen, suggesting no
attractive interaction between these two atoms. This
suggests that any association between water or
hydroxylic ligands with Cu(II) porphyrins can be
expected to mainly involve hydrogen bonding to the
nitrogens, rather than direct metal-oxygen
coordination. Indeed out of 242 structures identified
in the Cambridge Cristallographic datatabase [12]
only 7 contain Cu-O bonds; four have neutral oxygen
ligands [13-16] and the Cu-O bond in these is
particularly long (generally 2.5-2.7 Å) with the
exception of [16] where the protons of the water
ligand bound to the Cu are strongly interacting with
the hexafluoroantimonate anions presumably giving
water a partial anionic character and allowing it to lie
within 2.2 Å of the Cu. Also, of the 242 structures
only five others contain axial ligands to the Cu (one
with Cl [17] and four with N [18-20]), all with bond
lengths between 2.4-2.6 Å. All of these experimental
data are therefore in good agreement with the
calculations reported here (Table-2).
Table-3 shows the evolution of energy for
models 2-7 upon elongation of the axial bond lengths
by 1 Ǻ. These values provide an estimate of the axial
bond strength, since in the elongated structures the
Cu-axial ligand distances are all higher than the sum
of van der Waals radii. These bond strengths are
larger in structures 3, 4, and 5, where the ligands are
anionic and the bonds are shorter (Cu-L distances of
2.18 Å, 2.11 Å, respectively 2.08 Å, cf. Table-2)
compared to structures 2 and 6 (Cu-L distances of
2.71 Å respectively 3.17 Å, as the ligand-macrocycle
bonds are essentially hydrogen-bonding in nature).
When nitrite binds in an O-coordinate fashion to
copper (structure 4), the Cu---O bond is stronger by
~3 kcal/mol compared to Cu---N bond from N-
coordinate binding mode (structure 3), in contrast to
the case of the similar iron (II) and (III) and cobalt
(II) and (III) complexes, where the N-nitrite isomer
was preferred [9]. The energy differences computed
for models 2 and 6 (Table-3) suggest essentially
identical binding energies (~2.6 kcal/mol) even
though the number of hydrogen bonds between the
ligand and the macrocycle differs (two with water,
one with phenol). The weakness of these hydrogen
bonds (~half compared to a typical strong hydrogen
bond) suggests that compounds 2 and 6 are unlikely
to be found as stable static structures in solution. In
structure 7, where the imidazole ligand is neutral, the
Cu---N bond is relatively weak (ΔE=4.7 kcal/mol,
comparable to the energy of a strong hydrogen bond);
such weakness of the axial bonds, especially with
imidazole or thiolate ligands, has also been noted
with iron porphyrins [21].
Table-4 shows computed Mulliken atomic
spin densities for models 1-7 (Fig. 3). The differences
between the copper spin densities in these 7
structures are not major, as the values range from
0.67 to 0.73. The nitrogen spin density, with values
between 0.083 and 0.064, is relatively small but,
summed up over the four nitrogen atoms, does
amount to an ~30% of the spin density being
delocalized away from the copper. As expected, the
orbitals with unpaired electrons are dx
2
-y
2
with lobes
pointing to the four nitrogen atoms (Fig. 3). Part of
the spin density is also localized in the dyz orbital
(structure 5), while in structure 6 the dxz and dz
2
orbitals are also involved (cf. Table-5).
4. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
408
Fig. 2: Optimized geometries for models 1-7.
Table-2: Calculated Cu-X (X=O, N), N(porphyrin)-H(ligand) and Cu-porphyrin plane (Cu-P) distances, in Å.
No. Cu-N1 Cu-N2 Cu-N3 Cu-N4 Cu-N* Cu-P Cu-O N1-H1 N2-H2 Cu-N5
1. 2.00 2.00 2.00 2.00 2.00 0.00 - - - -
2. 2.02 2.02 2.00 2.00 2.01 0.06 2.71 2.48 2.51 -
3. 2.05 2.05 2.05 2.05 2.05 0.34 - - - 2.18
4. 2.05 2.05 2.06 2.06 2.05 0.45 2.11 - - -
5. 1.96 2.1 1.96 2.05 2.01 0.23 2.08 - - -
6. 2.02 2.00 2.00 2.00 2.00 0.02 3.17 2.16 - -
7. 2.02 2.02 2.03 2.03 2.02 0.22 - - - 2.36
*average of the Cu-N bonds lengths
Table-3: Energy variation for models 2-7 upon
elongation of the axial bond lengths by 1 Ǻ.
No. ΔE (kcal/mol)
2 2.58
3 13.3
4 16.4
5 10.6
6 2.60
7 4.70
In structures 2 and 6 the spin densities on
the four nitrogen atoms are larger than for most
models, except model 1 (Table-6). In these two cases
there is no copper-oxygen interaction, which makes 2
and 6 very similar to 1. Comparing structures 2 and 7
with in structure 7, which has proper axial ligation,
the interaction between copper and nitrogen from
imidazole decreases the spin density on the four
nitrogen atoms of the porphyrin to a value of 0.073 as
compared to the 0.079 seen in structure 2. The
hydrogen bonds affect the nitrogen spin density,
insofar as nitrogens involved in such hydrogen bonds
tend to have somewhat less spin density; indeed, spin
density in nitrogen is inversely correlated with the
total charge, and a higher charge would be required
for efficient hydrogen bonding.
5. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
409
Fig. 3: Spin densities computed for models 1-7.
The influence of ligands on Cu-porphyrin
electronic structure is unexpectedly small, compared
to what one might have expected based on the
notably different changes induced by each ligand
(imidazole, nitrite, guaiacol and ABTS) on the EPR
superhyperfine splitting [5]. Indeed, the copper g┴
signal (g=2.06) displays superhyperfine coupling
from the four nitrogen atoms of the porphyrin leading
to a complex pattern with peak-to-peak distance of 17
G. While this coupling is almost unobservable in the
starting material (aqueous copper porphyrin), it
becomes detectable with distinctly different
intensities in the several spectra shown in ref. [5]. A
small difference is observed in spin densities at the
copper and at the porphyrin nitrogen atoms in
structures 3 and 4 comparatively with structure 1,
where copper has no axial ligand. Copper spin
density increases under the nitrite axial ligation
influence (from 0.67 in structure 1 to 0.72 and 0.73 in
structures 3 and 4), while nitrogen spin densities
decrease (from 0.080 in structure 1 to 0.067 and
0.064 – 0.066 in structures 3 and 4) (Table-4). In the
EPR spectra, the superhyperfine coupling emerges
notably detectable in presence of nitrite as axial
ligand [5], which is the opposite of what one would
expect based on the trends of spin density on
porphyrin nitrogens computed by DFT. Phenolate as
copper axial ligand in structure 5 has the same effect
as nitrite on copper and nitrogen spin densities, while
for protonated phenol as ligand (in structure 6), the
differences are much smaller (Table-4). Comparing
these results with EPR spectrum [5] of CuTPPs with
guaiacol and ABTS which shows significant
superhyperfine coupling, the experimental data not
only indicates more considerable changes in the
electronic structure than computations, but also, as in
the case of nitrite as ligand, an opposite trend to what
is expected based on DFT-derived nitrogen spin
densities. In structure 7, imidazole increases copper
spin density (from 0.67 in structure 1, to 0.70) and
decreases spin density in porphyrin nitrogen atoms
(from 0.080 in structure 1 to 0.073), while the
changes induced by this ligand in the EPR
superhyperfine splitting are much larger and again of
opposite nature [5]. This is unexpected, and leads to
the more detailed analyses reported below.
The trend in the magnitude of
superhyperfine coupling effects seen in the
experimental EPR spectra is (phenolic
system)>imidazole>nitrite [5]. One would expect to
see the same trend followed by DFT-derived spin
densities. This trend can be supported if one assumes
non-protonated phenol as ligand, but not if phenolate
coordination is considered.
6. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
410
Table-4: Calculated Mulliken atomic charges and atomic spin densities for models 1-7 in vacuum. Values for
the porphyrin and axial ligands are 0.00, and therefore not shown.
No. Cu (charge) Cu N1 N2 N3 N4 N1+N2+N3+N4
1. 0.85 0.670 0.080 0.080 0.080 0.080 0.320
2. 0.82 0.690 0.079 0.075 0.079 0.075 0.310
3. 0.78 0.720 0.067 0.067 0.067 0.067 0.270
4. 0.76 0.730 0.064 0.066 0.064 0.066 0.260
5. 0.80 0.730 0.064 0.064 0.064 0.064 0.260
6. 0.82 0.670 0.083 0.076 0.080 0.080 0.320
7. 0.88 0.700 0.073 0.074 0.073 0.073 0.290
The copper Mulliken atomic charges for
models 1-7 are shown in Table-5. Copper charges in
structure 1, where there is no axial ligand and in
structure 7 have larger values, 0.85 and 0.88
respectively. In structures with anionic axial ligands,
3, 4 and 5, copper charges are smaller, 0.78, 0.76 and
0.80, which is partly due to a different overall charge
of the model in these systems. In structures 1, 2, 6
and 7 the copper atomic spin densities values are
smaller, but the atomic charges are larger than in
structures 3, 4 and 5 (Table-4).
Table-5 illustrates that in models 5 and 6
(with phenol and phenolate as axial ligands) the net
spin density at the copper is partly due to
contributions of two other d orbitals, leaving even
less spin in the dx2-y2 – the orbital directly pushing
spin density onto the nitrogens. This is again at odds
with expectations based on the EPR spectra, where
the phenol-type systems seem to have the largest
amount of spin delocalization towards to porphyrin
nitrogens.
Table-5: Copper d occupied orbitals (NPA analysis).
No. d orbitals Cu
1. x2
-y2
0.69
2. x2
-y2
0.70
3. x2
-y2
0.74
4. x2
-y2
0.74
5. x2
-y2
0.59
yz 0.16
6. xz 0.16
x2
-y2
0.48
z2
0.06
7. x2
-y2
0.72
Single point calculations for models 1-7
were also performed in water. The influence of
solvation on Cu-porphyrin spin densities is minor, cf.
Table-6. In structure 1 solvation produces no change,
most likely because the molecule is symmetrical to
the point where its dipole moment is zero. In the
models involving neutral ligands, the computed spin
densities are smaller than in vacuum, which implies,
as discussed above when examining hydrogen
bonding to water and phenol, an expected increase in
polarization of the Cu-nitrogen bonds. In the models
involving anionic ligands, the spin density values of
the porphyrin nitrogen atoms increase from 0.067 in
vacuum to 0.071 in water in model 3, respectively
from 0.064 to 0.068, for models 4 and 5 (Table-6),
while the copper spin densities decrease.
Table-6: Calculated Mulliken atomic charges and
atomic spin densities in water. Values for the
porphyrin and axial ligands are 0.00, and therefore
not shown.
No.
Cu
(charge)
Cu N1 N2 N3 N4 N1+N2+N3+N4
1. 0.86 0.670 0.080 0.080 0.080 0.080 0.320
2. 0.85 0.680 0.079 0.076 0.079 0.076 0.310
3. 0.83 0.700 0.071 0.071 0.071 0.071 0.280
4. 0.82 0.710 0.068 0.069 0.068 0.069 0.270
5. 0.89 0.720 0.068 0.067 0.067 0.068 0.270
6. 0.85 0.67 0.083 0.077 0.080 0.080 0.320
7. 0.93 0.67 0.073 0.074 0.073 0.073 0.290
Solvation also induces minor changes in the
copper atomic charges: these decrease under the
influence of water in all models, but more in
structures with anionic axial ligands 3 (from 0.83 to
0.78), 4 (from 0.82 to 0.76) and 5 (from 0.89 to 0.80)
(Table-6). An inverse correlation between copper
Mulliken atomic spin densities and copper Mulliken
atomic charges in structures 1-7 is maintained in
solvent compared to vacuum (Table-6) – which, as
pointed out above, is mostly due to differences in
overall charges on the models. Calculations in
solvent thus indicate only minor changes in Cu-
porphyrin electronic structure in presence of axial
ligands.
The additional structures 8-11 (Fig. 4) were
also optimized, in order to verify if calculations on
more realistic models can provide better agreement
with the EPR spectra [5]. As seen in Fig. 5 and in
Table-7, models 8 and 10 remain planar after
optimization. In models 9 and 11 the copper is
slightly displaced out of the porphyrin plane, with
slightly longer Cu-N distances (Table-7). In general
thus, the overall geometry of the macrocycle is only
marginally affected by the lateral substituents.
7. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
411
Fig. 4: Laterally-substituted models employed in present study.
Fig. 5: Optimized geometries for models 8-11.
8. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
412
Table-7: Calculated Cu-N distances (Å).
No. Cu-N1 Cu-N2 Cu-N3 Cu-N4 Cu-N* Cu-N5
8. 2.01 2.01 2.01 2.01 2.01 -
9. 2.04 2.05 2.04 2.05 2.04 2.28
10. 2.00 2.00 2.00 2.00 2.00 -
11. 2.03 2.03 2.03 2.03 2.03 2.35
*average of the Cu-N bonds lengths
The spin densities computed for copper and
nitrogen in models 8 and 9 are similar to those in 10
and 11 (Table-8). The copper charges are larger in
the methylated structures 9 and 11 (0.95 and 0.92),
than in structures 8 and 10 (0.90 and 0.86) (Table-8).
Comparing structures 8 with 9 and 10 with 11,
copper charges and copper spin densities increase in
both cases as an effect of imidazole ligation, while
the spin densities in the four porphyrinic nitrogen
atoms decrease (Table-8). Nevertheless, these
differences still do not appear significantly different
in magnitude compared to those observed in the
smaller models.
Table-8: Calculated copper Mulliken atomic charges
and atomic spin densities for models 8-11 in vacuum.
No. Cu (charge) Cu N1 N2 N3 N4
8. 0.90 0.670 0.079 0.079 0.079 0.079
9. 0.95 0.720 0.069 0.072 0.069 0.071
10. 0.86 0.670 0.080 0.080 0.080 0.080
11. 0.92 0.700 0.073 0.074 0.073 0.074
Single point calculation on structures 3, 5, 6
and 7 were also performed using a different
functional (BP86) and in a different software package
[10]. The results were qualitatively identical to those
discussed so far. However, the same BP86 in a third
software package [9] yield entirely different data.
Spin densities computed for this latter case are shown
in Fig. 6. Notably, in structures 3 and 5 the spin
density is clearly delocalized onto the axial ligand,
contrary to the results seen in the other computational
packages. As seen in Table-9, the copper spin
densities computed by this alternative method are
distinctly smaller than those in Table-4; moreover, in
structure 3 significant spin densities is delocalized on
nitrogen atom from nitrite, and to some extent a
similar observation can be made on structure 5. These
results in Fig. 6 may be taken to be in good
agreement with the notable changes induced by each
ligand (imidazole, nitrite, guaiacol and ABTS) on the
EPR superhyperfine splitting [5]. This poses an
unexpected paradox and underlines concerns which
may be formulated with respect to population
analyses based on DFT calculations in transition
metal complexes – even at the qualitative level.
Fig. 6: Spin densities computed for structure 3, 5, 6 and 7 with Spartan 5.
9. Roxana-Viruca Ţolan, Alexandru Lupan and J.Chem.Soc.Pak., Vol. 38, No. 03, 2016
Radu Silaghi-Dumitrescu
413
Table-9: Calculated copper Mulliken atomic charges and atomic spin densities for models 3, 5, 6 and 7 with
Spartan 5.
Nr. Cu (charge) Cu N1 N2 N3 N4 N5 O1 O2
3.
5. 0.55 0.510 0.066 0.075 0.074 0.065 - 0.038 -
6. 0.48 0.500 0.094 0.084 0.090 0.090 - 0 0
7. 0.50 0.520 0.086 0.087 0.087 0.087 - - -
Conclusion
DFT calculations using a rather standard
functional and basis set indicate minor changes in
Cu-porphyrin electronic structure in presence of axial
ligands, while in CuTPPs EPR spectra ligands as
nitrite, guaiacol and ABTS induce considerable
changes on the superhyperfine coupling. However, a
different computational package reveals a
qualitatively different picture of the spin density
delocalization, in much better agreement with
experiment and posing an interesting methodological
problem from the computational point of view.
Acknowledgment
The work shown here has been supported by
the Romanian Ministry for Education and Research
project PCCE 312/2008.
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