Coordination Compound
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Coordination Compound (c) Polydentate ligands: A ligand that is attached to a central metal
ion by bonds from two or more donor atoms.
(d) Chelating ligands: Polydentate ligands whose structures permit
(I) Perfect Complexes the attachment of two or more donor site to metal ion simultaneously,
The compounds in which complex ion is fairly stable thus resulting in cyclic structure are called chelating ligands and
and further dissociation is not possible or only feebly compound formed is known as chelate compound.
dissociation is possible in solution state. (e) Ambidentate ligands: Ligands which can ligate through two
(II) Imperfect Complexes
difference atoms present in it are called ambidentate ligands. At a
Those complexes in which complex ion is less stable
and is reversibly dissociates to give enough simple time only one atom can donate.
ions and thus respond to their usual qualitative test. (f) Flexidentate Ligands: Ligands which sometimes do not use all
Classification of Ligands the donor sites to get coordinated with central metal ion are known as
(A) Based on Charge flexidentate ligands.
(i) Neutral ligands H2O, NO, CO, C6H6 etc. (B) Based upon bonding interaction between the ligand and the
(ii) Positive ligands NO+, N2H5+
central atom.
(iii) Negative ligands (i) Classical or simple ligands: These ligand only donate the lone
pair of electrons to the central atom.
(a) Unidentate/monodentate ligands : Ligands
(ii) Non classical or 𝜋-acid or 𝜋-acceptor ligand: These ligand not
which donate one pair of electron to the central
metal are called unidentate ligands. only donate the lone pair of electrons to central metal but also accept
(b) Bidentate ligands: Ligands which have two the electron cloud from central atom. On the basis of nature of
donor atoms and have the ability to link with central donating electron cloud these ligands are following types.
metal ion at two position are called bidentate (a) 𝝈 donor 𝜋 acceptor Ex. CO, CN-
ligands. (b) 𝜋 donor 𝜋 acceptor Ex. C2H2, C6H6
Heading Spectrochemical Series
● A spectrochemical series is the arrangement of
common ligands in the increasing order of their Coordination Compound
crystal-field splitting energy (CFSE) values.
● The ligands present on the R.H.S of the series are
strong field ligands while that on the L.H.S are weak
field ligands.
● Also, strong field ligands cause higher splitting in the d
orbitals than weak field ligands.
I− < Br− < S2− < SCN− < Cl− < N3 < F− < OH− < C2O42− ∼
H2O < NCS− ∼ H− < CN− < NH3 < en ∼ SO32− < NO2− <
phen < CO
Rule For IUPAC Nomenclature
(a) Like simple salts, the positive part of the coordination
compound is named first.
Ex. K4[Fe(CN)6] the naming of this complex starts with
potassium.
(b) Then after ligands of the coordination sphere are to
be named.
(c) The ligands can be neutral, anionic or cationic.
(i) The neutral ligands are named as the molecule
Ex. C5H5N pyridine, (C6H5)3P Triphenylphosphine,
H2N一CH2一CH2一NH2 ethylene diamine.
CO carbonyl, NO nitrosyl, H2O Aqua, NH3 amine.
(ii) Anionic ligands ending with ‘ide’ are named by
replacing the ‘ide’ with suffix ‘O’.
Coordination Compound
Crystal Field Theory
Valence Bond Theory
The drawbacks of VBT of coordination compounds are to a
(a) The metal ion under the influence of ligands can use its
considerable extent removed by the Crystal Field Theory).
vacant d(n-1), ns, np, nd orbitals for hybridisation.
Factors Influencing the Magnitude of C.F.S.E
1. Higher the CFSE value higher will be the stability of
complex
2. Chelated complexes are more stable than non-chelated
Stability of Coordination Compound
complexes given the donor atoms are same
The stability of a coordination compound [MLn] is measured in
3. Same charges on the cation but the number of
terms of the stability constant (equilibrium constant, Kf).
d-electrons is different
Coordination Compound Classification of Isomerism
Type of Isomerism
Stereo Isomerism
They have same molecular formula, same
constitution, they differ only with respect to the
special orientation of ligands in space around the Structural isomerism
metal ion. Ionization
Geometrical Isomerism
(i) The ligands occupy difference positions around Hydrate
the central metal ion.
(ii) When two identical ligands are coordinated to the
metal ion from same side then it is cis isomers. Coordination
Geometrical isomers with coordination number =
4(Square planar complexes) Linkage
Ma4, Ma3b, M(AA)2, M(AA)a2, M(AA)ab, M(AB)a2,
M(AA)(AB), M(AA)(BB) can’t show GI.
[Pt(NH3)2Cl2] Cis(Cis-Platin) anti cancer Ligand
Stereo Isomerism
Geometrical
Optical
Organo-metallic Compounds
Coordination Compound The compounds in which metal carbon linkage is present are known
as organo-metallic compounds.
1. 𝝈-bonded organometallic compounds 𝝈-bond between metal
Bonding in coordination compounds and carbon.
Due to presence of p acid ligands special type of 2. 𝜋-bonded organometallic compounds
bonding takes place in coordination compounds. It is (i) 𝝈-donar and 𝜋-acceptor [Ni(CO)4], [Fe(CO)5] etc.
known as synergic bonding. (ii) 𝜋-donar and 𝜋-acceptor [Fe(C2H5)2], [Cr(C6H6)2] etc.
Bonding in metal carbonyl Sidgwick Theory or Effective
Ex. [Fe(CO)5] ; [Ni(CO)4] ; [Cr(CO)6] Atomic Number Concept (EAN)
EAN = (atomic number of the metal-oxidation state of central metal) +
number of electrons gained from the donor atoms of the ligands.
Werner’s Co-ordination Theory
Werner’s co-ordination theory was the first attempt to explain the
bonding in co-ordination compounds.
Werner’s Representation of Complex
(i) Fe(NH3)6Cl3 Dotted lines indicate
primary valency and
continuous lines indicate
secondary valency of metal
ion.
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