CHM 113A
General
Chemistry
Inorganic Chemistry: Crystal Field Theory, Structure of
Coordination Complexes, Metalloenzymes,
Apparao Draksharapu, PhD
Organometallic Chemistry, Oxidative Addition, appud@iitk.ac.in
Reductive Elimination, Insertion Reactions, Monsanto
Acetic Acid Process, Hydrogenation, Hydroformylation,
and Ziegler- Natta Polymerization.
d-block Metals or Transition Metals
• Many d-block metals are
relevant to biology: V to Zn
and Mo, Cd and W.
• Roles of di-block metals in
biology include global cycling
of N, C, H; biosynthesis of
vitamins and
deoxynucleotides; respiration;
photosynthesis, small
molecule transportation, redox
reactions, etc.
• d-block metals are heavily
employed as catalysts in
pharmaceutical and chemical
companies.
d-block Metals or Transition Metals
Hemoglobin • Many d-block metals are
OEC in PS-II
relevant to biology: V to Zn
and Mo, Cd and W.
• Roles of di-block metals in
biology include global cycling
of N, C, H; biosynthesis of
vitamins and
deoxynucleotides; respiration;
photosynthesis, small
molecule transportation, redox
reactions, etc.
Ziegler-Natta
Polymerization
• d-block metals are heavily
employed as catalysts in
Cytochrome c pharmaceutical and chemical
Oxidase
companies.
Structure of Organic Compounds
Coordination Complexes
M
1 L
L 3
2 M
L M L L L
C’s valency is 4 M M
5 6 7 8 9
Coordination Complexes
• A key feature of TM is their ability Ligands
to form complexes with small
molecules and ions called :NO2- :NO3- :CN- :SCN- :NCS-
ligands. 2e- 2e- 2e- 2e- 2e-
• The central metal ions can :OH- :OH2 :NH3 :CO :NO+
attract electron density, usually 2e- 2e- 2e- 2e- 2e-
a lone pair of electrons from
another atom or molecule to
form a coordination complex. Transition metals
• Donor atoms are called Ligands
(Lewis base typically donate one
pair of electrons)
• Acceptor atoms are transition
metals (Lewis acid, accept one
pair of electrons)
Ligands
It is an ion or polar molecule capable of donating a pair of electrons to the central atom via a donor atom.
Types of Ligands:
• Monodentate Ligands: Ligands with only one donor atom. NH3, Cl-, F-, H2O, CO, PR3, CN- etc.
• Bidentate Ligands: Ligands with two donor atoms, e.g.
L L L X X X
Ligands
• Tridentate Ligands: Ligands which have three donor atoms per ligand.
• Tetradentate/polydentate ligands: Ligands which have multi donor atoms per ligand
Coordination Complexes/Compounds
Coordination sphere
[Ni0(CO)4]
Ionizable anion outside
the coordination sphere
Ni
Overall charge of the complex
III
Central metal
Ligand
Possible Geometries
[CoIII(NH3)6]3+.3Cl- or [CoIII(NH3)6]Cl3
Coordination number (CN) is 6.
It can vary from 2-12, 6 is very common CN = 2 CN = 3 CN = 4 CN = 5 CN = 6
CN: It is the total number of ligands Linear TP SP Td TBP SP Octahedral
attached to the central metal atom
180◦ 120◦ 90◦ 109.5◦ 90◦, 120◦ 90◦ 90◦
through coordinate bond
History: Werner’s Theory
Alfred Werner (Nobel Prize, 1913) developed a model of coordination complexes which
explains the following observations
CoIIICl3.6NH3
NH3 CoIIICl3.5NH3
CoIICl2
Air CoIIICl3.4NH3
CoIIICl3.3NH3
[CoIII(NH3)6]Cl3 3 AgCl CoIIICl3.6NH3 4 ions
[CoIII(NH3)5Cl]Cl2 2 AgCl CoIIICl3.5NH3 Conductivity in 3 ions
aq. Ag+ aq. solution
[CoIII(NH3)4Cl2]Cl 1 AgCl CoIIICl3.4NH3 2 ions
[CoIII(NH3)3Cl3] 0 AgCl CoIIICl3.3NH3 0 ions
History: Werner’s Theory
[CoIII(NH3)6]Cl3 [CoIII(NH3)6]3+ + 3 Cl-
[CoIII(NH3)5Cl]Cl2 [CoIII(NH3)5Cl] 2+ + 2 Cl-
[CoIII(NH3)4Cl2]Cl [CoIII(NH3)4Cl2] + + 1 Cl-
[CoIII(NH3)3Cl3] [CoIII(NH3)3Cl3] + 0 Cl- (neutral)
Central metal in the coordination complex exhibits two types of valencies, primary valency (oxidation state) is
ionizable, and non-directional, secondary valency (coordination number) is non-isolable and directional
(directed towards fixed position in space), every metal has a fixed number.
Central Metal Oxidation State
Ligand
[CoIII(NH3)6]3+ [Co?(NH3)6]
Charge of the Complex
Coordination Sphere
Coordination Number
Oxidation Number
• It is the charge which central atom appears to have if all the ligands are removed along
with the electron pairs that are shared with the central atom.
• Knowing the charge on a metal complex ion and charge on each ligand, one can
determine the oxidation number for the central metal ion.
• Knowing the oxidation number on the metal and the charges on the ligands, one can
calculate the charge on the complex ion.
[Cr?(H2O)4Cl2]NO3 [Cu?(NH3)4]2+ [Cr(H2O)4Cl2]?
x + 4(0) + 2(-1) = +1 x + 4(0) = +2 +3 + 4(0) + 2(-1) = x
x + 0 + (-2) = +1 x + 0 = +2 3 + 0 + (-2) =x
x = +3. i.e., M = Cr3+ x = +2. i.e., M = Cu2+ x = +1. i.e., [Cr(H2O)4Cl2]+
Geometry of Metal Complexes
[PtII(NH3)2Cl2]
[CoIII(NH3)5Cl]2+ MA5B Cis Trans
Cis-platin is an anti cancer drug, where as
trans-platin doesn’t work. Hence,
geometry/isomerism plays a key role in the
[CoIII(NH3)4Cl2]+ MA4B2 chemical and physical properties of metal
complexes.
Isomerism
Isomerism is the phenomenon in which more than one coordination compounds having the same
molecular formula have different physical and chemical properties due to different arrangement of
ligands around the central metal atom.
Isomerism
Structural Stereo
Isomerism Isomerism
Ionization Hydration Linkage Coordination Geometrical Optical
Isomerism Isomerism Isomerism Isomerism Isomerism Isomerism
Ionization Isomers
Ionization isomers result from the interchange of an anionic ligand within the first
coordination sphere with an anion outside the coordination sphere.
Examples:
1. [CrIII(NH3)4ClBr]NO2 and [CrIII(NH3)4ClNO2]Br
2. [CoIII(NH3)4Br2]Cl and [CoIII(NH3)4ClBr]Br
3. [PtIV(en)2Cl2]Br2 and [PtIV(en)2Br2]Cl2
Hydration/Solvate Isomers
Hydration isomers result from the interchange of H2O and another ligand between the first
coordination sphere and the ligands outside it.
The exchange of free solvent molecules such as water, ammonia, alcohol etc. in the crystal lattice
with a ligand in the coordination entity will give different isomers. If the solvent molecule is
water, then these isomers are called hydrate isomers.
Example: The complex with chemical formula CrIIICl3.6H2O has three hydrate isomers as
shown below.
[CrIII(H2O)6]Cl3 [CrIII(H2O)5Cl]Cl2.H2O [CrIII(H2O)4Cl2]Cl.2H2O
Linkage Isomers
Linkage isomers may arise when one or more than one atom of the ligands can
coordinate to the metal ion in more than one way (these type of ligands are called
ambidentate ligands).
e.g., in [SCN]-, both the N and S atoms are potential donor sites.
Example of Linkage Isomers
[Co (NH3)5(NCS)]
III 2+
in Redox Reactions
[CoIII(NH3)5(NCS-N)]2+ [CoIII(NH3)5(NCS-S)]2+
2+ 2+
Coordinate Isomers
Coordination isomers are possible only for salts in which both cation and
anion are complex ions; the isomers arise from interchange of ligands
between the two metal centers.
[CoIII(NH3)6][CrIII(CN)6] and [CrIII(NH3)6][CoIII(CN)6]
[CoIII(NH3)6][CoIII(NO2)6] and [CoIII(NH3)4(NO2)2][CoIII(NH3)2(NO2)4]
[PtII(NH3)4][PtIVCl6] and [PtIV(NH3)4Cl2][PtIICl4]
Isomerism
Isomerism is the phenomenon in which more than one coordination compounds having
the same molecular formula have different physical and chemical properties due to different
arrangement of ligands around the central metal atom.
Isomerism
Structural Stereo
Isomerism Isomerism
Ionization Hydration Linkage Coordination Geometrical Optical
Isomerism Isomerism Isomerism Isomerism Isomerism Isomerism
Stereoisomers
Similar to organic compounds, coordination compounds also exhibit stereoisomerism. The
stereoisomers of a coordination compound have the same chemical formula and
connectivity between the central metal atom and the ligands. But they differ in the spatial
arrangement of ligands in three-dimensional space. They can be further classified as
geometrical isomers and optical isomers.
Geometrical Isomers
• Geometrical isomerism exists in heteroleptic complexes due to different possible three
dimensional spatial arrangements of the ligands around the central metal atom. This
type of isomerism exists in square planer and octahedral complexes.
• Distinguishing between cis- and trans-isomers of a square planar complex or between mer-
and fac-isomers of an octahedral complex is most unambiguously confirmed by structural
determinations using single-crystal X-ray diffraction.
Geometrical Isomers
In square planar complexes of the form [MA2B2]n± and [MA2BC]n± (where A, B and C are mono dentate
ligands and M is the central metal ion/atom), similar groups (A or B) present either on same side or
on the opposite side of the central metal atom (M) give rise to two different geometrical isomers,
and they are called, cis and trans isomers, respectively.
Cis Trans
MA2B2
MA2BC
Geometrical Isomers
The square planar complex of the type [M(xy)2]n± where xy is a bidentate ligand with two different
coordinating atoms also shows cis-trans isomerism. Square planar complex of the form
[MABCD]n± also shows geometrical isomerism. In this case, by considering any one of the ligands (A,
B, C or D) as a reference, the rest of the ligands can be arranged in three different ways leading to
three geometrical isomers.
Cis Trans
M(XY)2
MABCD
Geometrical Isomers in Octahedral Complexes
MA5B: Only one ligand out of six ligands that binds to metal differs and hence only one
isomer is possible
MA4B2: If two ligands in an octahedral complex are different from the other four, giving an
MA4B2 complex, two isomers are possible. e.g. Cis- and trans-[Co(NH3)4Cl2]Cl
https://chem.libretexts.org
Geometrical Isomers in Octahedral Complexes
MA3B3: Replacing another A ligand by B in MA4B2 gives an MA3B3 complex for which there
are also two possible isomers
Facial isomer: The three ligands of each kind occupy opposite triangular faces of the
octahedron is said to be called Facial isomer
Meriodional isomer: The three ligands of each kind lie on what would be the meridian if
the complex were viewed as a sphere is said to be called Meridional isomer
fac-[RhIIICl3(Py)3]
mer-[CoIIICl3(NH3)3]
Geometrical IsomersM(AA)
in Octahedral
B
Complexes
2 2
M(AA)2B2 : Two
M(AA) cis and one trans isomer
2B2: AA is a bidentate ligand; three stereoisomers (2 cis- and 1
trans- are possible.
[Co III(en) Cl ]+ Where+en =
Example 2 [Co(en)
2 2Cl2]
Ethylenediamine (en)
Mirror plane Mirror plane
trans-
cis-
Non-superimposable mirror images Superimposable mirror images
cis- isomer of MAA2b2 may also exhibit optical isomerism
Optical Isomers
• Optical isomers are related as non-superimposable mirror images and differ in the
direction with which they rotate plane-polarized light.
• These isomers are referred to as enantiomers or enantiomorphs of each other and their
non-superimposable structures are described as being asymmetric.
• Their solutions rotate the plane of the plane polarized light either clockwise or
anticlockwise and the corresponding isomers are called 'd' (dextro rotatory) and 'l' (levo
rotatory) forms, respectively.
• Various methods have been used to denote the absolute configuration of optical isomers
such as R or S, and Λ or Δ.
• The octahedral complexes of type [M(xx)3]n±, cis-[M(xx)2AB]n± and cis-[M(xx)2B2]n± exhibit
optical isomerism.
Optical Isomers
M(AA)3 [CoIII(en)3]3+ [M(AA)2B2] cis-[CoIII(en)2Cl2]+
The two optical isomers of [CoIII(en)3]3+ have identical trans-[CoIII(en)2Cl2]+
chemical properties and just denoting their absolute
configuration does NOT give any information regarding the N N
direction in which they rotate plane-polarised light.
This can ONLY be determined from measurement and then
the isomers are further distinguished by using the prefixes N N
(-) and (+) depending on whether they rotate left or right.
