Physical and analytical studies of transition metal complexes

1. PHYSICAL & ANALYTICAL
STUDIES of TRANSITION
METAL COMPLEXES
By
Dr/ Huda Eid AbdelWahab

2. • Transition metal complexes
• Transition Metal complexes properties
Geometry
Stereoisomerism
Magnetism
colored complexes
Stability
Catalytic properties
• Analytical studies
Classical methods
Instrumental methods

3. Transition metal complexes
• Complex ion has a metal ion at its center with
a number of other molecules or ions
surrounding it, which attached to the central
ion by coordinate (dative covalent) bonds.
• The molecules or ions surrounding the central
metal ion are called ligands
• All ligands are lone pair donors, all ligands
function as Lewis bases.
Transition
metal
complex
metal
ion
ligand
Transition metal (element) is an element that
can form at least one stable ion that has a
partially filled d subshell
d orbital partially filled

4. Ligand types
Mono-dentate
(lone pair of electrons)
Neutral
Ex: water, ammonia
Anion
Ex: chloride ion
Bi-dentate
(two lone pairs)
Ethylenediamine,
oxalate
Polydentate
quadridentate
(four lone
pairs)
Hemoglobin
Hexadentate
(six lone
pairs
EDTA

5. Example: Fe(H2O)6
3+
• Iron has the electronic structure 1s22s22p63s23p63d64s2
(Fill up 4s before 3d), When it forms an Fe3+ ion it loses the 4s
electrons and one of the 3d electrons to leave 1s22s22p63s23p63d5
(Remove from 4s before 3d)
at the bonding level:
Now, be careful! The single electrons in the 3d level are NOT involved in
the bonding in any way. Instead, the ion uses 6 orbitals from the 4s, 4p
and 4d levels to accept lone pairs from the water molecules.
Before they are used, the orbitals are reorganized (hybridised) to
produce 6 orbitals of equal energy.

6. Transition Metal
Complexes Properties
Geometry
Stereoisomerism
Magnetism
Colored complexes
Stability
Catalytic properties

7. 1- Geometry
linear
• Coordination
number = 2
• Ex:
[Ag(NH3)2]+
• [Ag(CN)2]-
• [Cu(Cl)2]-
tetrahedral
• Coordination
number = 4
• Ex: [Cu(Cl)4]2-
• [Co(Cl)4]2-
Square planar Octahedral
• Coordination
number = 4
• Ex:
Pt(NH3)2Cl2
• Coordination
number = 6
• Ex:
[Fe(CN)6]3-
• [Cr(NH3)4Cl2]+

8. 2- Stereoisomerism
2.1. Geometric isomerism
2.2. Optical isomerism
2.3. Structural isomerism

9. 2.1. Geometric isomerism
• This occurs in square planar complexes like the Pt(NH3)2Cl2 , cis :
when two ligands are adjacent, trans : when opposite each other.
• In octahedral complexes: When three identical ligands occupy one
face of an octahedron facial (fac). If these three ligands and the
metal ion are in one plane meridional (mer).
• fac-[CoCl3(NH3)3] mer-[CoCl3(NH3)3]

10. 2.2. Optical isomerism
• Occurs when a molecule is not superimposable with its
mirror image

11. 2.3. Structural isomerism
• Occurs when the bonds are themselves different.
• Ionization isomerism
The isomers give different ions in solution although they have the same composition.
[Co(NH3)5Br]SO4 [Co(NH3)5SO4]Br
BaCl2 BaCl2
whit ppt -Ve
• Linkage isomerism
Occurs with ambidentate ligands that can bind in more than one place.
For example: NO2 , SCN
• Coordination isomerism
This occurs when both positive and negative ions of a salt are complex ions and the two
isomers differ in the distribution of ligands between the cation and the anion.
[Co(NH3)6][Cr(CN)6] [Cr(NH3)6][Co(CN)6]

12. 3- Magnetic Properties
Diamagnetic
Paired electron
Spin cancel
No net magnetic effect
[repel by magnetic
field], Zn+2
Weak repulsion
Octahedral (low-
spin), and square-
planar complexes
Paramagnetic
Unpaired electron
Net spin
Net magnetic effect
[attracted by
magnetic field], Mn+2
Weak attraction
Octahedral (high-
spin), and Tetrahedral
complexes
Ferromagnetic
Fe, Co, Ni
certain
materials
(such as iron)
form
permanent
magnets
Strong

13. Different coloures
formation
Different
transition
metal
MnCl2 pink
NiCl2 yellow
Different
ligand
NiCl2
yellow
NiSO4
green
Ni(NO3)2
Violet
Different
oxidation
state
V3+ green
V2+ violet
Complex
stereochemistry
4- Transition metal complex color

14. Color formation: 3d orbital splitting by ligand
• Color in transition metal complexes is generally due to electronic transitions (by
the absorption of light) of two principal types:
1- d-d transitions.
2- charge transfer transitions.

15. 5- Stability
• The affinity of metal ions for ligands is described by
stability constant. This constant, also referred to as the
formation constant Kf can be calculated through the
following method for simple cases:
(X)Metal(aq) + (Y)Lewis Base(aq) ⇌ (Z)Complex
Kf = [Complex]z / [Metal]x [Lewis Base]y
• Large values indicate that the metal has high affinity for
the ligand, provided the system is at equilibrium
Kd = 1/Kf
Kd is the decomposition constant

16. 6- Catalytic properties
Energy of 3d and 4s
orbital's are very close
(Use 3d and 4s electrons
to form weak bond)
Multiple oxidation states
( lose and gain electron
easily)
Catalytic activity

17. Analytical studies
Classical methods
Qualitative
analysis
Chemical
test
Flame test
Quantitative
analysis
Gravimetric
Volumetric
(titration)
Instrumental methods
Spectroscopy
analysis
UV-VIS
spectroscopy
Infra red
spectroscopy
NMR
Atomic absorption
AAS
Mass
X-ray
Separation analysis
Paper
chromatography
Column
chromatography
HPLC
GC

18. Classical methods
Qualitative analysis
• Chemical test
Based on reactions that produce a gas
with distinctive properties, or a colour
change produced by adding a reagent
or the production of a precipitate
• Flame test
Used to detect the presence of certain
elements, based on each element's
characteristic emission spectrum
Quantitative analysis
• Gravimetric
Add reagent precipitation
Filtration draying
weight
• Volumetric
Titration: this method involves the
measurement of volume of
a solution of known concentration
which is used to determine the
concentration of the analyte

19. Separation analysis
1- Paper Chromatography (Thin
Layer Chromatography)
• Chromatography can be used to
identify substances and check on
the purity of a substance
• Stationary phase (chromatography
paper , silica gel sheets, or on
glass sheet.
• Mobile phase : solvent
2- Column chromatography
• Used to isolate chemical
compound from a mixture. Column
chromatography is able to
separate substances based on
differential absorption of
compounds to the absorbent
• To purify liquids (and solids.)

20. 3- Gas chromatography (GC)
• A sample of the substance under
investigation is injected and
vaporized into a tube containing
a carrier gas (mobile phase). The
mobile phase must be an inert or
unreactive gas like nitrogen
4- High performance liquid
chromatography (HPLC)
• Used to separate, identify, and
quantify each component in a mixture.
• It relies on pumps to pass a
pressurized liquid solvent containing
the sample mixture through a column
filled with a solid adsorbent material.
• Each component in the sample
interacts slightly differently with the
adsorbent material, causing different
flow rates for the different
components and leading to the
separation of the components as they
flow out the column.

21. Instrumental methods
1- UV-VIS Spectroscopy
• Used for the quantitative determination of transition metal
ions ( concentration)
•Solutions of transition metal ions can be colored (i.e., absorb visible
light) because d electrons within the metal atoms can be excited from
one electronic state to another.
•The color of metal ion solutions is strongly affected by the presence of
other species, such as certain anions or ligands.
The Beer-Lambert law A= log10 (Io/ I) = ϵ c L

22. 2- Infra-red spectroscopy
• Infra-red spectrum can be used to identify the ligand structure in the transition
metal complex.
• The examined compound absorb some IR frequencies, and the rest of
frequencies which passed through the compound will appear on the detector.
• How much of a particular frequency gets through the compound is measured as
percentage transmittance.
fingerprint
region

23. 3- Atomic absorption spectroscopy
• To defined the metal ion and determine its
concentration in the complex solution

24. 4- Nuclear magnetic resonance NMR
• Used to identify the complex structure

25. 5- Mass spectroscopy
• In order to measure the characteristics of
individual molecules, a mass spectrometer
converts them to ions so that they can be
moved by external electric and magnetic fields. The three
1. The Ion Source : A small sample is ionized, usually to cations
by loss of an electron.
2. The Mass Analyzer : The ions are sorted and separated according to
their mass and charge.
3. The Detector : The separated ions are then measured, and the results
displayed on a chart.

26. 6- X-ray crystallography
• Used for structure determination
• X-ray crystallography is a technique used
for determining the atomic and molecular
structure of a crystal
• A crystallographer can produce a three-
dimensional picture of the density of
electrons within the crystal.
• From this electron density, the mean
positions of the atoms in the crystal can be
determined, as well as their chemical
bonds, their disorder, and various other
information.

27. References
• F. A. Cotton, G. Wilkinson - Advanced Inorganic Chemistry, sixth
edition, A WILEY-INTERSCIENCE PUBLICATION JOHN WILEY &
SONS, INC.1999
• https://www.chemguide.co.uk/inorganic/complexions
• Analytical Chemistry of the Transition Elements by Harry M. N. H.
Irving & Alan T. Hutton, the Encyclopedia of Inorganic Chemistry, First
Edition. 2006

28. Thank you