class 12th coordination compounds

2.  CO-ORDINATION COMPOUNDS :- It is an addition compound ,which is
obtained by combining two or more stable compounds in any molar
ratio.
Or
Molecular or addition compounds (obtained by evaporating the solution of
two compounds in molar proportions) which retain their identies even
when dissloved in water or any other solvent and having properties
completely different from those of the constituents are called complex
or coordination compounds .
e.g CuSO4 + 4NH3 [Cu(NH3 )4 ]SO4 [Cu(NH3)4] 2+SO4
2-
COORDINATION COMPOUND


3. DOUBLE SALT
1.They exist only in the solid
state .In aqueous solution ,they
dissociates completely into ions.
2.They usually contain two
simple salts in equimolar
proportions.
3.The properties of the double
salts are same as those of its
constituents compounds .
4.In a double salts, the metal
ions show their normal valency.
5.A double salt loses its
identity in the solution.
COMPLEX COMPOUNDS
1.They exist in the solid state as
well as in aqueous solution .This
is because even in the solution ,the
complex ion does not dissociate
into ions .
2.The simple salts from which
thery are formed may or may not
be in equimolar proportions.
3.The properties of the
coordination compound are
different from its constituents.
4.In a coordination compound
,metal ion satisfies its two types of
valencies callled primary and
secondary valencies.
5. A coordination compound
(complex) retains its identity in the
solution.

4.  Those compounds in which the central metal
atom/ion is linked to a number of ions or neutral
molecules by Coordinate bond, are called Co-
ordination compounds e.g [Ni(CO)4 ]
In this complex four CO molecules are linked to
central metal atom (Ni) by co-ordinate bond .
Or
Such compounds which retain their identity even
when dissolved in water or in any other solvent are
called coordination compounds.

5.  COMPLEX ION
It may be defined as the electrically charged radical which
consists of central metal atom /ion surrounded by a group of
ligands .In complex ion,metal ion is surroundedby anumber
of oppositely charged ions or molecules more than its normal
valency.
e.g [Cu(NH3)4] 2+ , [Fe(CN)6] 4-
 Types of complexes
 Depending upon the type of charge on the complex ion,are of
three types.
 (i). Cationic complexes : If the complex ion carries net
positive charge, it is known as cationic complex.
 e.g [Co(NH3)6] 3+ , [Ni(NH3)6] 2+

6.  If the complex ion carries net negative charge,it is called as anionic complex.
 e.g [Ag(CN)2] - , [Fe(CN)6] 3- etc.
 (iii) Neutral complexes :
 A complex which has no net charge is called neutral complex.
 e.g [CoCl3(NH3)3] , [Ni(CO)4] etc
 CENTRAL METAL ATOM OR ION
 The cations to which one or more neutral molecules or anions are attached is
called central metal atom or ion.
 e.g [Co(NH3)6]2+ , Co2+ is the central metal ion.
 LIGANDS
 Anions or neutral molecules which are linked to the central metal ion through
co-ordinate bonds are called ligands. e.g H2O ,NH3,CO, Cl- ,Br- ,I-
 In the complex ion , [Cr(NH3)6]3+ ,the Cr3+ is the central metal ion and
molecules of NH3 are the ligands, In the complex ion , [Ni(NH3)6]2+ ,the Ni2+
 is the central metal ion and molecules of NH3 are the ligands, Central atom
/ions are also reffered to as Lewis acids.
 In most of the complexes ,ligands acts as donor of one or more lone pairs of
electrons to the central metal atom/ion. It should be noted that in metallic
carbonyl ,the ligands ,CO, acts as both donor or acceptor.
 (M CO)

7.  1.UNIDENTATE /MONODENTATE LIGAND
 If there is only one donor atom in the ligand,it is called unidentate ligand. E.g
 NH3 , H2O , Cl- , Br- ,I-
 2.BIDENTATE LIGAND
 If there are two donor atoms in the ligand, it is called bidentate ligand.
 E.g oxalate ion , ethylene diamine
 3. TRIDENTATE LIGANDS
 The ligands having three coordination sites are called tridentate ligands.
 E.g diethylenetriamine
 4.POLYDENTATE LIGANDS
 If there are four or more donor atom in the ligand,it is called polydentate ligands.
Depending upon the number of donor sites,these ligands may be termed as
tetradentate (four donor atoms ) pentadentate (five donor atoms) and hexadentate
(six donor atoms ) e.g EDTA


 -OOCH2C CH2COO-

 N- CH2- CH2- N
 -OOCH2C CH2COO-
 Ethylenediaminetetraacetate ligand (EDTA)

8.  WERNER’S CO-ORDINATION THEORY
 Several theories were proposed to explain the observed properties of Co(III)
ammines and of other similar compounds like Pt(IV) ammines .it bwas only in
1809,that Werner presented a theory known as Werner’s coordination thoery
which could explain all the observed properties of complex compounds.
Important postulates of this theory are:
 1.Most elements exhibit two types of valencies: (a) primary valency and (b)
secondary valency:
 (a) Primary valency or ionizable valency: This corresponds to the oxidation
state of the metal ion.This is also called principal ,ionisable or ionic valency.It
is satisfied by negative ions and its attachment with the central metal ion is
shown by dotted lines.
 This type of valency is understood by considering simple salts like AgNO3
 CuSO4 , CoCl3,PtCl4 .
 Here ,primary valency of Ag,Cu, Co and Pt are 1,2,3 and respectively,These
valencies are non-directional.

9.  It is also termed as coordination number(usually abbreviated as CN ) of the
central metal ion. It is non-ionic or non ionisable (i.e coordinate covalent
bond type ) .This is satisfied by either negative ions or neutral molecules.
The ligands ,which satisfy the coordination number are directly attached to
the metal atom or ion and are shown by thick lines. In modern terms, while
writing down the formula of complex,these valencies are shown in square
brackets [ ], i.e these form the coordination sphere of metal atom or ion. The
ion shown outside the bracket , i.e , coordination sphere are ionizable in
solution form
 2. Every element tends to satisfy both its primary and secondary valencies.In
order to meet this requirement a negative ion may often show a dual
behaviour, i.e it may satisfy both primary and secondary valencies (since in
every case the fulfillment of coordination number of the central ion appears
essential ). Such dual behaviour valencies are not ionized .
 3.Every metal atom has fixed number of secondary valencies or coordination
number.
 4.The secondary valencies are directed towards fixed positions in space. It is
the basis of stereochemistry of metal complexes. For example, a metal
complex ion with coordination number four has either tetrahedral or square
planar geometry. Similarly, a complex ion with coordination number six is
octahedral in shape, while two secondary valencies are arranged in a linear
way.

10.  1. [Co(NH3)6]Cl3 2. [Co(NH3)5 Cl] Cl2
 NH3 Cl
 NH3 Cl NH3 NH3
 NH3
 Cl Co Cl Co Cl
 NH3 Cl NH3 NH3 NH3
 NH3 NH3
 3. [Co(NH3)4 Cl2]Cl 4.[Co(NH3)3 Cl3]
 Cl Cl
 NH3 NH3 NH3 NH3
 Co Cl Co
Cl Cl
 NH3 NH3 NH3
 Cl

11.  Werner was the first to explain the properties of co-ordination
compounds.However, his theory could not answer the following
basic questions :
 (i) Why the bonds in co-ordination compounds are directional in
nature ?
 (ii) Why do coordination compounds possess definite magnetic and
optical properties ?
 (iii) Why only certains elements form the coordination compounds
and not all the elements ?
 UTILITY OF WERNER’S THEORY
 1. It helps to explain the behaviour of coordination which could not
be otherwise explained on the basis of electronic theory of valency.
 2.It helps in providing an explanation of isomerism in compounds .
It also predicts the existance of isomers of the type which had not
previously been observed.

12.  This theory was proposed by pauling to explain the bonding in co-ordination compounds. It is based
on the following assumptions.
 1. The first basic assumptions made is that metal –ligand bond arises by the donation of electron pair
by ligands to the metal atom or metal ion
 2.In the formation of a complex ion , the metal atom or ion makes available a requisite number of
vacant orbitals for the formation of co-ordination bonds with suitable ligands. The no. of vacant
orbitals made available is equal to the co-ordination no. of centarl metal ion .
 3.Hybridisation of appropriate orbitals (s, p and d ) occurs to give a set of equivalent orbitals having
definite qeometry such as tetrahedral, square planar,octahedral etc.
 4.both the inner nad outer d-orbitals i.e (n-1)d and nd orbitals can take part in hybridisation.
 5.Each ligand contains a donar atom which has a filled orbiatl containing lone pair of electrons.
 6.The vacant orbitals of central metal ion overlap with filled orbitals of the l;igands resulting into co-
ordinate bonds.
 7.The vacant orbitals hybridise together to form hybrid orbitals which are the same in number as the
atomic orbitals hybridising together. These hybrid orbitals are vacant, equivalent in energy and have a
definite energy.
 8.The non-bonding metal electrons occupies the inner orbitals and they do not take part in the
hybridisation .The electrons are grouped in accordance with the hunds’s rule of maximum
multiplicity.However under the influence of a strong ligand ,they may be forced to pair up against the
Hund’s rule.
 9.in addition to the -bond , a bond may be formed by overlap of a filled metal d-orbitals with a
vacant ligand orbital (M L).This usually happens in complexes of metals ions of low oxidation
states.
 10.If the complex contains unpaired electrons , the complex is paramagnetic in nature, whereas, if it
does not contain any unpaired electron , the complex is diamagnetic in nature.

13. Coordination
Number
Type of
hybridizations
Arrangement Examples
1 sp3 Tetrahedral [CuCl4 ]2- ,[MnCl4 ]2- etc
2 dsp2 Square planar [Cu(NH3 )4]2+ ,[Ni(CN)4 ]2- etc
3 d2sp3 or sp3d2 Octahedral [Fe(CN )6]4- ,[Fe(CN)6 ]3- etc

14.  Examples of octahedral complexes having co-ordination number=6
 1. [Co(NH3 )6]3+ ion
 E.C of Co = [Ar]18 3d7 4s2
 Co3+ = [Ar]18 3d6
 Co =
4s2 4p
Co3+ =
3d6 d2sp3 Hybridisation
[Co(NH3 )6 ]3+ =
NH3 NH3 NH3 NH3 NH3 NH3
Octahedral geometry
Magnetic character --- diamagnetic
3d7
XX XX XX XX XX XX

15.  1. [EDTA]4- Is a
 (a) Monodentate ligand
 (b) Bidentate ligand
 (c) Quadridentate ligand
 (d) hexadentate ligand

