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![The C–O stretching wavenumbers are shifted to lower values when
there are changes in the extent of backbonding in the compound.
Removing positive charge from the metal causes the shift of
electrons from the metal to the CO π∗ orbitals causes the CO
wavenumber values to decrease. The highest excess of negative
charge on the metal occurs in the [V(CO)6 ]− complex and so more
backbonding occurs than in the other complexes. The next highest
excess of electron density is in Cr(CO)6 , and then [Mn(CO)6 ]+.](https://image.slidesharecdn.com/spectroscopicmethodsininorgchem-160210034625/85/Spectroscopic-methods-in-Inorganic-Chemistry-35-320.jpg)
Uploaded byChris Sonntag
Spectroscopic methods in Inorganic Chemistry
This document provides an overview of spectroscopic methods in inorganic chemistry, focusing on infrared (IR) spectroscopy. It discusses key concepts like dipole moments, factors that influence bond vibrational frequencies, and using symmetry to determine vibration modes. Specific applications covered include identifying functional groups, distinguishing between cis and trans transition metal carbonyl complexes using IR spectra, and analyzing metal-ligand vibrations in complexes. The document also lists several online resources for IR spectral simulation, prediction, and reference databases.
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Spectroscopic methods in Inorganic Chemistry
- 1. Spectroscopic Methods in InorganicChemistry Dr.Chris UP Feb 2016
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- 5. Polarity and Dipolemoments Dipole moment can be calculated as the product of the charge (abbreviated Q) times the distance (abbreviated r) between the charges.
- 6. The dipole momentof HCl is 1.03 D, and the bond length is 127 pm. What is the percent ionic character of the HCl bond? First we will assume that this molecule is 100% ionic. In this case, the charges are separated by the bond length, and we can calculate the dipole moment in this extreme case. The actual dipole moment measured for this molecule is 1.03 D, so the molecule is not completely ionic. http://wps.prenhall.com/wps/media/objects/4678/4791085/ch10_01.htm
- 7. Why do CO2and CCl4 do not have a dipole moment ?
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- 11. Types of motions Stretch: symmetricasymmetric wagging twisting scissoring rocking Bending: http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Infrared_ Spectroscopy/Infrared%3A_Theory
- 12. WHAT INFLUENCES THE WAVENUMBEROF A BOND ?
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- 17. Normal modes ofvibration Triatomic molecules
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- 21. Which peaks belong tostretching or bending ?
- 22. Planar BF3 molecules Howmany degrees of freedom ? (bond vibrations without rotation and translation) 1 2
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- 32. IR / RamanSimulation www.molwave.com
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- 35. The C–O stretchingwavenumbers are shifted to lower values when there are changes in the extent of backbonding in the compound. Removing positive charge from the metal causes the shift of electrons from the metal to the CO π∗ orbitals causes the CO wavenumber values to decrease. The highest excess of negative charge on the metal occurs in the [V(CO)6 ]− complex and so more backbonding occurs than in the other complexes. The next highest excess of electron density is in Cr(CO)6 , and then [Mn(CO)6 ]+.
- 36. Character of theM-CO bond Slightly antibonding HOMO
- 37. Electron density onthe metal Higher C-O strength Lower C-O strength M=C=O character
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- 39. CO IR vibrations Wecompare cis- and trans-ML2(CO)2 complexes in IR: What are the point groups ? 39
- 40. Tetrahedral Td OctahedralOh Linear: D∞h for A-B-A ( i ) C ∞h for A-B http://en.wikibooks.org/wiki/Introduction_to_Mathematical_Physics/N_body_problem_in_quantum_mechanics/Molecules 40
- 41. Character Tables forcis and trans 41
- 42. Representations of 2C-O groups Which contains the irreducible representations : Which contains the irreducible representations : Conclusion: Number of IR peaks for cis and trans complex: 42
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- 45. The spectra presentedin Figure 5.6 show a trend in the wavenumber shifts for the three hexamine complexes; the N–H bands shift to lower wavenumbers from Co to Cr to Ni. This indicates that the N–H bond order (bond strength) decreases as the metal–N bond order increases in the stability order mentioned
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- 56. How can weexplain the difference to Fe(III) ?
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- 59. IR Spectrum of“Rennie” Example: identify products in Antacids http://www.ptfarm.pl/pub/File/Acta_Poloniae/2000/2/083.pdf (1) Carbonate Compound
- 60. Ref. spectra Mg CO3 CaCO3 O-HCa-O Mg-O
- 61. (2) Hydroxy Compounds IRof “Maalox (an)” IR of “Alusal”
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- 69. How do youdistinguish whether the structure of transition metal complex molecule M(CO)4L2 is cis or trans by inspection of the CO stretching region of the IR spectra? -> determine the symmetry group: CO substitution pattern
- 70. -> Check thecharacter tables: c2v d4h
- 71. Reducing stretching motions 4stretching vectors 4 0 0 2 4 0 0 0 0 0 0 4 2 0
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- 74. ATR Method –attenuated total reflection
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