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CO-ORDINATION COMPOUNDS &
ORGANOMETALLICS
BONDING
1. [Ni (CN) 4]2At no. of Ni = 28

 
3d



4s
4p
[Ni (CN) 4]2X + 4 * (-1) = (-2)
X = ( -2 ) + 4
X = +2
Ni2+
   

[Ni (CN) 4]2- is diamagnetic & square planar

 
3d

4s
4p
Hybridization is dsp2
2. [NiCl4] 2At. no. = 28
Ni2+
   

[Nicl4]2- is paramagnetic & has tetrahedral geometry


3d



4s
4p
Hybridization sp3
i.e., the geometry of the co ordination entity can be predicted if its magnetic behaviour
is known.
3. [Fe (CN)6]4At. No. = 26
X + 6 * ( -1 )= ( -4 )
X= +2
Fe






Fe2+
 



[Fe(CN)6]4- is diamagnetic & octahedral
Fe2+ hybridization is d2sp3
4. [Cr(NH3)6]3+
At. No. = 24
X + 0 * 6 = +3
X = +3
Cr3+ 21 eParamagnetic, octahedral
Hybridization d2sp3
5. [Fe(CN)6]3X + 6 * ( -1 ) = ( -3 )
X= +3
At. No. = 26
Fe3+
23 e-
Paramagnetic, octahedral
Hybridization d2sp3
  
6. [Fe(H2O)6]3+
At. No. = 26
Fe3+
Paramagnetic, octahedral
sp3d2
7. [Co(NH3)6]3+
Z= 27
X + 6 * ( -1 ) = ( -3 )
X= +3
Diamagnetic, octahedral
Hybridization d2sp3
8. [Co F6]3Paramagnetic, octahedral
Hybridization sp3d2
9. [NiCO4]
Diamagnetic, tetrahedral
Hybridization sp3
10. [Zn(NH3)4]2+
Diamagnetic, tetrahedral
sp3
WERNER’S CO-ORDINATION THEORY

Metals exert two types of linkages
1. The primary or ionizable links.
These are satisfied by negative ions, and equal the ox. No. of metals.
2. The secondary or non ionizable links.
These are satisfied by neutral or negative ions/groups. The secondary
linkages equal the co ordination no. of central metal atom/ion. This no. is
fixed for a metal.

Ions/groups bound by secondary linkage have characteristics spatial
arrangements. Spatial arrangements are called coordination polyhedra.
LIGANDS



In the formation of coordination bonds, the anions or neutral molecules act as
electron pair donors.
The atom donating electron pair is called donor atom
The donor atom, molecule, or anion which donate pair of electrons to metal atom
are called ligands
e.g. NH3, H2O, Cl-, OH-, CN-
CO-ORDINATION ENTITY/SPHERE



The central metal atom and the ligands which are attached to it are enclosed in a
square bracket are collectively called co-ord. sphere.
The species present in co-ord. sphere is non ionizable.
The species present in ionization sphere is ionizable.
e.g. [Cu (NH3) 6] SO4
MONODENTATE, BIDENTATE, & POLYDENTATE LIGANDS

If the ligands contain only one donor atom it is called monodenate.
E.g. NH3, H2O, Cl-

If the ligand contains two donor atoms, it is called bidentate ligands.
E.g. COOCH2-NH2
|
|
COOCH2-NH2
Oxalate ion

Ethylene diamine
Ligands having more than two donor atoms are called polydentate ligands.
EXAMPLES
Tridentatee.g. diethylene triamine
CH2-NH-CH2
|
|
CH2
CH2
|
|
NH2
NH2
Tetradentate –
e.g. triethylene tetraamine
Hexadenatee.g. EDTA
-
HOOCH2C
-
2
CH2COOHN-CH2-CH2-N
HOOCH C
CH2COOH-
CHELATING LIGANDS


When a multidenate ligand coordinates to a metal ion by more than one donor
atom, then a ring like structure obtained is called chelate ring.
The ligand is called chelating ligand.
e.g. CH2-CH2
|
|
NH2 NH2
Ethylene diammine
CO-ORDINATION NUMBER (CN)
The total no. of monodenate ligands attached to the central metal atom or cation is called
coordination number of central atom
[Ag (CN)2]2-
CN=2
[Cu (NH3)4]2+
CN=4
CO-ORD NO. OF SOME CATIONS
Fe2+
Fe3+
Cr3+
Co3+
Pt4+
Ag+
Ni2+
Ni0
Cu2+
Au2+
Al3+
6
6
6
6
6
2
4, 6
4
4, 6
4
4
NOMENCLATURE
Formula Writing





Cation is written first whether simple or complex, followed by anion.
Co-ord. sphere is written in square brackets.
The ligands are written on the right side of metal in order of anionic, neutral and
cationic ligands.
The polyatomic ligands are written in small brackets
Alphabetical order is maintained for same type of ligands, viz anionic, neutral
and cationic.
Nomenclature






Cation whether simple or complex is named first followed by name of anion.
Ligands are named alphabetically. (NOT anion first then the neutral and last
cation)
Negative ligands have ending O.
Neutral ligands have no special ending.
NH3=ammine, H2O=aqua, CO=carbonyl
Positive ligands have ending in –ium.
NO+=nitrosonium,
NO2+=nitronium
Organic ligands have their own name.
NH2CH2CH2NH2=ethylene diammine
LIGANDS
CN-
Cyano
Br-
Bromo
Cl-
Chloro
I-
iodo
NO2
Nitro
ONO-
Nitrito
NO3
Nitrato
SCN-
Thiocyanato
NCS-
Iso thiocynate
O2
oxo
SO32
Sulphito
SO42
Sulphate
S 2 O32
Thio sulphato
CO32
Carbonato
NH3
Ammine
H2O
Aqua
NO
Nitrosyl
CO
Carbonyl
CS
Thiocarbonyl
PH3
Phosphine
NO+
Nitrosonium
NO2
Nitronium
COO|
COOCH2-NH2
|
CH2-NH2
oxalato
Ethylene diammine
EXAMPLES
[CrCl2 (H2O)4]NO3
Tetraaquadichloro chromium(III)nitrate
K3[Fe (C2O4)3]
Potassium trioxalato ferrate(III)
K[PtCl3 (NH3)]
Potassium ammine trichloro platinate(II)
[CoCl2 (en)2]SO4
Dichloro bis(ethylene diammine)cobalt (IV)sulphate
[Cr (H2O)6]Cl3
Hexaaqua chromium (III)chloride
[CoCl (ONO) (en)2]+
Chlorobis(ethylene diammine)nitrito cobalt (III)
nitrate
Pentaammine carbonato cobalt (III)chloride
[Co(CO3) (NH3)5]Cl
[PtCl2 (NH3)4][PtCl4]
[CoCl (NO2) (NH3)4]NO3
Tetraamminedichloro platinum(IV)tetrochloro
platinate(II)
Tetraamminedichloro cobalt(III) hexacyano
chromate(III)
Tetraammine chloronitro cobalt(III)nitrate
K[Co (CN)(CO)2(ONO)]+
Potassium dicarbonyl cyanonitrito cobaltate(II)
[CoCl2 (NH3)4]3[Cr (CN)6]
ISOMERISM IN CO-ORD. COMPOUNDS
Structural Isomerism
 Ionization isomerism
 Hydrate isomerism
 Linkage isomerism
 Co-ordination isomerism
Ionization Isomerism
Due to exchange of groups within the complex ion and ions outside it.
[Co (NH3)5Br]SO4 & [Co (NH3)5SO4] Br
[CoNO3 (NH3)5]SO4 & [CoSO4 (NH3)5] NO3
Hydrate Isomerism
 [CoCl(H2O)(NH3)4]Cl2 & [CoCl2(NH3)4]Cl.H2O
 [CoCl(H2O)(NH3)4]Br2 & [CoBr2(NH3)4]Cl.H2O
Linkage Isomerism
The difference between the linkages creates linkage isomerism.
 [Cr(SCN)(H2O)5]3+ & [Cr(NCS)(H2O)5]2+
 [Co(NO2)2(py)2(NH3)2]NO3 & [Co(ONO)2(py)2(NH3)2]NO3
Co ordination isomerism
When positive and negative ions are complex, isomerism may be caused by the
interchange of ligands between the anions and cations.
 [Co(NH3)6][Cr(CN)6] & [Cr(NH3)6][Co(CN)6]
 [Co(en)3][Cr(CN)6] & [Cr(en)3][Co(CN)6]
STEREO ISOMERISM
Geometrical isomerism
Consider a square planar complex of the formula MA2B2, the two possible isomerism are
B
A
B
M
B
M
A
CIS
A
A
B
TRANS
Cl
NH3
Cl
NH3
Pt
Pt
Cl
NH3
NH3
CIS
Cl
TRANS
Optical Isomerism
When the isomers show different optical activity towards the plane of polarized light, the
phenomenon is called optical isomerism.
[Co (en)2 cl2]+
Cl
Cl
Cl
Cl
en
en
en
en
DOUBLE SALTS AND CO ORDINATION COMPOUNDS
Mohr’s salt FeSO4 (NH4)2SO4.6H2O
Potash alum K2SO4.Al2 (SO4)3.24H2O
are double salts.
They exist only in the solid state and loose their identity when dissolved in water.
E.g. Aq. Solution of potash alum will give the tests of K+, Al3+ and SO42- ions.
Coordination compounds retain their identity in solid as well as in dissolved state.
In aq. Solution they do not furnish all simple ions, but give complex ions.
CRYSTAL FIELD THEORY
 This theory is based on the assumption that there is electrostatic interaction
between metal ion and ligands.
 In metal ions all fixed orbitals have same energy.(degenerate orbitals)
 On the approach of ligands electrons in d orbitals will be repelled by electron of
ligands.
 The repulsion will increase the energy of d orbitals.
 Since d orbitals have different orientations they experience different interactions
from ligands.
 Thus, 5 degenerate d orbitals of metals split into 2 different sets of orbitals having
different energies in the presence of electrical fields of ligands.
 This splitting is called crystal field splitting.
In octahedral complexes, the 5 d orbitals split up into 2 sets.
Dx 2  y 2 & D z 2 of higher energy called eg orbitals.
Dxy, dyz & dxz of lower energy called t2g orbitals.
The energy difference between eg & t2g energy levels is called crystal field splitting
energy delta o (o- octahedral)
Ligands which cause only a small degree of crystal field splitting are called weak field
ligands and those which cause large splitting are called strong field ligands.
The arrangement of ligands on the bases of delta o is called spectrochemical series
I-<Br-<S2-<SCN-<Cl-<NO3-<F-<OH-<C2O42-<O2-<H2O<NCS-<py=NH3<CN-<CO
In general ligands above H2O are strong field ligands and below are weak.
Dx 2  y 2 , D z 2
Dxy, Dxz, Dyz
Splitting of d orbitals in octahedral crystal field
Dxy, Dxz, Dyz
Dx 2  y 2 , D z 2
In tetrahedral complexes, the d orbital splitting is inverted and smaller as compared to
octahedral field splitting.
LOW SPIN AND HIGH SPIN COMPLEXES
Strong field ligands form- low spin complexes.
Weak field ligands form- high spin complexes
[Fe (CN06]3Fe3+ has 3d5 electrons.
CN- is strong f ligand, and gives large delta o value. Therefore e- remains in lower set
and will pair up.
[Fe (CN) 6]3Low spin d2sp3
  

 
 
High spin sp3d2
   

 


[Fe (CN) 6]3-
Large delta o
Delta o -small
Delta o -large
[Co F6]3High spin Para
[Co (NH3)6]3+
Low spin dia
ORGANOMETALLIC COMPOUNDS
Compounds which contain at least 1 metal –carbon bonds.
They are classified into
1. Main gp organometallics.
2. d & f block organometallics
Main gp
e.g. CH3 Li
, B(CH3)3
, Si (CH3)4
d and f block organometallics
(CH3)2Zn
, Hg (CH3)2
Metal carbonyls
Ni
Fe
Fe (CO)5
Trigonal bypyramidal
Ni (CO)4
tetrahedral
Cr
Cr (CO)6
octahedral
BONDING IN CARBONYLS
CO as a ligand binds itself to metal through C atom to central atom.
CO is also an acceptor ligand as there are vacant pie molecular orbitals in CO.
This is called back bonding.
This stabilizes metal ligand interactions.
COLOUR IN CO ORDINATION COMPOUNDS




Color of coordination compounds can be explained on the basis of crystal field
theory
The energy difference between the 2 sets of d orbitals is very small
When visible light falls on them the e- gets raised from lower set of orbitals to
higher set of orbitals(e.g. in octahedral complexes from dxy, dyz, dxz to dx2-y2,
dz2 orbitals)
The transmitted light gives color to the complexes.