Class- XII Chemistry Chapter-9 Coordination...

Class- XII

Chemistry

Chapter-9

Coordination Compounds

Coordination compounds

contain a central atom (or cation) which is coordinated to a suitable number of anions

or neutral molecules and usually retain their identity in solution as well as in solid

state. These may be a positively charged, negatively charged or a neutral species,

[Co (NH3)6]3+, [NiCl4]2-, [Ni (CO)4] etc.

Werner’ Theory of Coordination Compounds:

Werner in 1898, propounded his theory of coordination compounds. The main

postulates are:

1. In coordination compounds metals show two types of linkages (valences)-primary

and secondary.

2. The primary valences are normally ionisable and are satisfied by negative ions.

3. The secondary valences are non-ionisable. These are satisfied by neutral molecules

or negative ions. The secondary valence is equal to the coordination number and is

fixed for a metal.

4. The ions/groups bound by the secondary linkages to the metal have characteristic

spatial arrangements corresponding to different coordination numbers.

In modern formulations, such spatial arrangements are called coordination polyhedra.

The species within the square bracket are coordination entities or complexes and the

ions outside the square bracket are called counter ions.

5. Octahedral, tetrahedral and square planar geometrical shapes are more common in

coordination compounds of transition metals. Thus, [Co (NH3)6] 3+ [CoCl (NH3)5] 2+ and

[CoCl2(NH3)4] + are octahedral entities, while [Ni (CO)4] and [PtCl4] 2– are tetrahedral

and square planar, respectively.

Difference between a double salt and a complex

Double salts dissociate into simple ions completely when dissolved in water. such as

carnallite, KCl.MgCl2.6H2O, Mohr’s salt,

FeSO4. (NH4)2SO4.6H2O, potash alum, KAl (SO4)2.12H2O, etc.

Complex ions do not dissociate into simple ions completely when dissolved in water

such as [Fe (CN)6] 4– of K4Fe (CN)6, do not dissociate into Fe2+ and CN– ions.

Some Important Terms Pertaining to Coordination Compounds:

(a) Coordination entity:

A coordination entity constitutes a central metal atom or ion bonded to a fixed

number of ions or molecules. For example, [CoCl3(NH3)3] is a coordination entity

in which the cobalt ion is surrounded by three ammonia molecules and three

chloride ions.

(b) Central atom/ion:

In a coordination entity, the atom/ion to which a fixed number of ions/groups

are bound in a definite geometrical arrangement around it, is called the central

atom or ion. For example, the central atom/ion in the coordination entities:

[NiCl2(H2O)4], [CoCl (NH3)5]2+ and [Fe (CN)6]3– are Ni2+, Co3+ and Fe3+, respectively.

These central atoms/ions are also referred to as Lewis acids.

(c) Ligands

The ions or molecules bound to the central atom/ion in the coordination entity

are called ligands. These may be simple ions such as Cl

H2O or NH3, larger molecules such as H

macromolecules, such as proteins.

Types of ligands

Unidentate ligand:

When a ligand is bound to a metal ion through a

NH3, the ligand is said to be unidentate

Bidentate ligand:

When a ligand can bind through two donor atoms as in H

diamine) or C2O42– (oxalate), the ligand is said to be

Polydentate:

When several donor atoms are present in a single ligand as in N(CH

ligand is said to be polydentate. Ethylenediaminetetraacetate ion (EDTA

important hexadentate ligand. It can bind through two nitrogen and four oxygen

atoms to a central metal ion.


These may be simple ions such as Cl–, small molecules such as

, larger molecules such as H2NCH2CH2NH2 or N(CH

macromolecules, such as proteins.

When a ligand is bound to a metal ion through a single donor atom, as with Cl

unidentate.

When a ligand can bind through two donor atoms as in H2NCH2CH2NH

(oxalate), the ligand is said to be didentate.

When several donor atoms are present in a single ligand as in N(CH

ligand is said to be polydentate. Ethylenediaminetetraacetate ion (EDTA



small molecules such as

or N(CH2CH2NH2)3 or even

single donor atom, as with Cl–, H2O or

NH2 (ethane-1,2-

When several donor atoms are present in a single ligand as in N(CH2CH2NH2)3, the

ligand is said to be polydentate. Ethylenediaminetetraacetate ion (EDTA4–) is an


Ambidentate ligand:

Ligand which can ligate through two different atoms is called ambidentate ligand.

Examples of such ligands are the NO

through nitrogen or through oxygen to a

can coordinate through the sulphur or nitrogen atom.

(d) Chelate:

When a di- or polydentate ligand uses its two or more donor atoms to bind a single

metal ion, it is said to be a chelate ligand. The number of such

the denticity of the ligand. Such complexes, called chelate complexes tend to be more

stable than similar complexes containing unidentate ligands

(e) Coordination number


Examples of such ligands are the NO2– and SCN– ions. NO2– ion can coordinate either

through nitrogen or through oxygen to a central metal atom/ion. Similarly, SCN

can coordinate through the sulphur or nitrogen atom.

or polydentate ligand uses its two or more donor atoms to bind a single

metal ion, it is said to be a chelate ligand. The number of such ligating groups is called


stable than similar complexes containing unidentate ligands


ion can coordinate either

central metal atom/ion. Similarly, SCN– ion

or polydentate ligand uses its two or more donor atoms to bind a single

ligating groups is called


The coordination number (CN) of a metal ion in a complex can be defined as the

number of ligand donor atoms to which the metal is directly bonded. For example, in

the complex ions, [PtCl6] 2– and [Ni (NH

6 and 4 respectively.

(f) Coordination sphere

The central atom/ion and the ligands attached to it are enclosed in square bracket and

is collectively termed as the coordination sphere. The ionisable groups are written

outside the bracket and are called counter io

K4[Fe(CN)6], the coordination sphere is [Fe(CN)

(g) Coordination polyhedron

The spatial arrangement of the ligand atoms which are directly attached to the central

atom/ion defines a coordination polyhedron about the central atom. The most

common coordination polyhedra are octahedral, square planar and tetrahedral. For

example,

[Co (NH3)6]3+ is octahedral, [Ni (

(h) Oxidation number of central

The oxidation number of the central atom in a complex is defined as the charge it

would carry if all the ligands are removed along with

with the central atom. The oxidation number is represented by a Roman numeral in

parenthesis following the name of the coordination entity. For example, oxidation

number of copper in [Cu (CN)

(i) Homoleptic and heteroleptic complexes:

in which a metal is bound to only one kind of donor groups, e.g.,

[Co (NH3)6] 3+, are known as homoleptic. Complexes in which a metal is bound to more

than one kind of donor groups, e.g.,

[Co (NH3)4Cl2] +, are known as heteroleptic.

Naming of Mononuclear Coordination Compounds

The following rules are used when naming coordination compounds:



and [Ni (NH3)4] 2+ the coordination number of Pt and Ni are



outside the bracket and are called counter ions. For example, in the complex

], the coordination sphere is [Fe(CN)6]4– and the counter ion is K

Coordination polyhedron




Ni (CO)4] is tetrahedral and [PtCl4]2– is square planar

Oxidation number of central atoms


would carry if all the ligands are removed along with the electron pairs that are shared



number of copper in [Cu (CN)4]3– is +1 and it is written as Cu(I).

Homoleptic and heteroleptic complexes:

in which a metal is bound to only one kind of donor groups, e.g.,

are known as homoleptic. Complexes in which a metal is bound to more

than one kind of donor groups, e.g.,

, are known as heteroleptic.

Naming of Mononuclear Coordination Compounds




the coordination number of Pt and Ni are



ns. For example, in the complex

and the counter ion is K+.




is square planar.


the electron pairs that are shared



are known as homoleptic. Complexes in which a metal is bound to more


(i) The cation is named first in both positively and negatively charged coordination

entities.

(ii) The ligands are named in an alphabetical order before the name of the central

atom/ion.

(iii) Names of the anionic ligands end in –o, those of neutral and cationic ligands are

the same except aqua for H2O, ammine for NH3, carbonyl for CO and nitrosyl for NO.

These are placed within enclosing marks ( ).

(iv) Prefixes mono, di, tri, etc., are used to indicate the number of the individual ligands

in the coordination entity. When the names of the ligands include a numerical prefix,

then the terms, bis, tris, tetrakis are used, the ligand to which they refer being placed

in parentheses. For example, [NiCl2(PPh3)2] is named as

dichlorobis(triphenylphosphine)nickel(II).

(v) Oxidation state of the metal in cation, anion or neutral coordination entity is

indicated by Roman numeral in parenthesis.

(vi) If the complex ion is a cation, the metal is named same as the element. For

example, Co in a complex cation is called cobalt and Pt is called platinum. If the

complex ion is an anion, the name of the metal ends with the suffix – ate. For example,

Co in a complex anion, [Co (SCN) 4]-2 is called cobaltate. For some metals, the Latin

names are used in the complex anions, e.g., ferrate for Fe.

(vii) The neutral complex molecule is named similar to that of the complex cation.

Bonding in Coordination Compounds

Valence bond theory:

It was given by Pauling in 1931

According to this theory, the metal atom or ion under the influence of ligands

can use its (n-1) d, ns, np or ns, np, nd orbitals for hybridisation to yield a set of

equivalent orbitals of definite geometry such as octahedral, tetrahedral, and

square planar.

These hybridised orbitals are allowed to overlap with ligand orbitals that can

donate electron pairs for bonding.

Number of Orbitals and Types of Hybridisations

ordination Number Type of hybridisation Shape of hybrid

4 sp3 Tetrahedral

4

5

6

6

Magnetic properties of coordination compounds:

A coordination compound is paramagnetic in nature if it has unpaired electrons and

diamagnetic if all the electrons in the coordination compound are paired.

Magnetic moment

For example:

For any coordination compound: To find the shape using valence bond theory

following steps to be followed

Remove the electrons from the metal and form it the ion

Rearrange metal electrons if necessary

Hybridization

Overlapping of hybrid orbitals of metal with ligand

Example: [Co (NH3)6]3+

In this central metal atom Co atomic no. is 27.

The electronic configuration of Co = (Ar)

Co3+=(Ar)183d6

Example [Fe (Co)5]: (inner orbital complex and diamagnetic)

dsp2 Square planar

sp3d Trigonal bipyramidal

sp3d2 Octahedral

d2sp3 Octahedral

Magnetic properties of coordination compounds:



where n is number of unpaired electrons


following steps to be followed

Remove the electrons from the metal and form it the ion

electrons if necessary

Overlapping of hybrid orbitals of metal with ligand

In this central metal atom Co atomic no. is 27.

The electronic configuration of Co = (Ar)183d74s2

orbital complex and diamagnetic)

Square planar

Trigonal bipyramidal

Octahedral

Octahedral



where n is number of unpaired electrons.


EXAMPLE: in [CoF6]3-…… (outer orbital complex and paramagnetic)

Drawbacks of valence bond theory:

This theory couldn’t have valid reason behind that why some complexes of

metal oxidation state is inner orbital while in some other complexes the same

metal atom ion in same state form outer orbital complex.

The magnetic behaviour explained wasn’t satisfactory

This theory couldn’t give the information about colour of compounds

This theory failed to distinguish between strong and weak ligand.

Crystal field splitting theory

It was given by Hans Bethe Ans John van vleck

Postulates

It assumes the central metal atom and ligands as point charges

When a complex is formed: central metal atom positive charge

Ligands –have negative charge

This theory considers the interaction between central metal atom and ligand is

purely electrostatic

When a complex is formed the central metalatom is surrounded by oppositely

charged ligands

No hybridization takes place

To form a bond the ligand molecule must approach towards central metal atom

In absence of external magnetic field, the d orbital of central metal atom is

degenerate but this degeneracy breaks when ligand approaches.

The d orbital splits into two sets:

Axial set non-axial set

dxy,dyz, dzx dx2-y2,dz2

This is crystal field splitting

Repulsive forces occur between electrons of metal and with lone pair ligands due to

which energy of electron fluctuate or changes.

For octahedral complexes

To form octahedral complex the ligands, have to approach central metal atom along

the coordination axis. During the approach the d orbitals whose lobes lie along the axis

will experience more repulsion due to this their energy will increase and the other

non-axial set will suffer less repulsion. as a result, the non-axial will have less energy as

compare to axial set (eg greater than t2g)

Tetrahedral complex:

The ligands have to approach central metal atom in between the coordinationaxis.

during the approach the d orbital’s whose lobes lie along the axis will experience less

repulsion due to this their energy will increase and the other non-axial set will suffer

more repulsion. as a result, the non-axial will have more energy as compared to axial

set (t2g greater than eg)

Square planar complex:

In the different order is seen i.e.

dx2-y2,dxy,dz2,dyz,dzx

Please note for all the complexes:

for strong ligands: the CFSE is more therefore pairing will occur

for weak ligands: the CFSE Is less

Spectrochemical series:

In general, ligands can be arranged in a series in the order of increasing field strength

as given below:

I –< Br–< SCN–< Cl–< S2–< F–< OH–< C2O42–< H2O < NCS–< edta4–< NH3< en < CN–< CO

Such a series is termed as spectrochemical series.

Please note for all the complexes:

for strong ligands: the CFSE(Δo) is more therefore pairing will occur

for weak ligands: the CFSE(Δo) Is less

(j) If Δo< P, the fourth electron enters one of the eg orbitals giving the configuration

t2g3eg

1. Ligands for which Δo< P are known as weak field ligands and form high spin

complexes.

(ii) If Δo> P, it becomes more energetically favourable for the fourth electron to occupy

a t2g orbital with configuration t2g4 eg

0. Ligands which produce this effect are known as

strong field ligands and form low spin complexes.

The limitations of crystal field theory:

The assumption that the interaction between metal-ligand is purely electrostatic

cannot be said to be very realistic.

This theory takes only d-orbitals of a central atom into account. The s and p

orbits are not considered for the study.

The theory fails to explain the behaviour of certain metals which cause large

splitting while others show small splitting. For example, the theory has no

explanation as to why H2O is a stronger ligand as compared to OH–.

The theory rules out the possibility of having p bonding. This is a serious

drawback because is found in many complexes.

The theory gives no significance to the orbits of the ligands. Therefore, it cannot

explain any properties related to ligand orbitals and their interaction with metal

orbitals.

Colour in Coordination Compounds

The crystal field theory attributes the colour of the coordination compounds to d-d

transition of the electron, i.e., the transition of electron from t2g level to the higher

eg level which accompanies the absorption of light in visible spectrum.

If absorption occurs in the visible region of the spectrum, then the transmitted light

bears a colour complementary to the colour of the light absorbed. The relationship

between the absorbed and transmitted wavelengths can be readily understood from

the following,

In the absence of ligands, crystal field splitting does not occur and

is colourless.

[Ti(H2O)6] 3+, which is violet in colour.

Anhydrous CuSO4 is white, but CuSO

[Ni(H2O)6] 2+(aq)+ en (aq) = [Ni(H

green pale blue

[Ni(H2O)4 (en)]2+(aq) + en (aq) = [Ni(H

blue/purple

[Ni(H2O)2(en)2] 2+(aq) + en (aq) = [Ni(en)

violet

Metal carbonyl

Metal carbonyls are homoleptic complexes in which carbon monoxide (CO) acts as the

ligand. Metal carbonyl, any coordination or complex compound consisting of a

heavy metal such as nickel, cobalt, or iron surrounded by

common metal carbonyls include:

Fe(CO)5, and octa carbonyl dicobalt Co

Considering bonding in metal carbonyls:

These compounds possess both s and p characters. The M

donation of lone pair of electrons

metal. The M-C pi bond is formed by the donation of pair of electrons from the filled d

orbital of metal into vacant antibonding pi orbital of carbon monoxide. The metal to

ligand bonding creates a synergic effect which strengthens the bond between CO and

metal as shown below: -

In the absence of ligands, crystal field splitting does not occur and hence the substance

which is violet in colour.

is white, but CuSO4.5H2O is blue in colour.

= [Ni(H2O)4(en)]2+(aq) + 2H2O

+ en (aq) = [Ni(H2O)2(en)2] 2+(aq) + 2H2O

+ en (aq) = [Ni(en)3] 2+(aq) + 2H2O


Metal carbonyl, any coordination or complex compound consisting of a

such as nickel, cobalt, or iron surrounded by carbonyl (CO) groups. Some

include: tetracarbonyl nickel Ni(CO)4, pentacarbonyl iron

dicobalt Co2(CO)8.

Considering bonding in metal carbonyls:

hese compounds possess both s and p characters. The M-C sigma bond is formed by

f electrons from the carbonyl carbon into a vacant orbital of

pi bond is formed by the donation of pair of electrons from the filled d



hence the substance


Metal carbonyl, any coordination or complex compound consisting of a

(CO) groups. Some

pentacarbonyl iron

C sigma bond is formed by

the carbonyl carbon into a vacant orbital of

pi bond is formed by the donation of pair of electrons from the filled d



Stability of Coordination Compounds

The stability of complex in solution refers to the degree of association between the

two species involved in the state of equilibrium. It is expressed as stability constant (K).

The factors on which stability of the complex depends:

(i) Charge on the central metal atom as the magnitude of charge on metal atom

increases, stability of the complex increases.

(ii) Nature of metal ion the stability order is 3d < 4d < 5d series.

(iii) Basic nature of ligands Strong field ligands form stable complex.

The instability constant or the dissociation constant of compounds is defined as the

reciprocal of the formation or stability Constant.

NCERT INTEXT QUESTIONS

Page No. 244

Answer.1

(i) [CO(NH3)4(H2O)2]Cl3.

(ii)K2[Ni(CN)4]

(iii)[Cr(en)3]Cl3

(iv)[Pt (NH3) Br Cl (N02)]–

(v)[PtCl2(en)2](N03)2

(vi)Fe4[Fe(CN)6]3

Answer.2

(a) hexaamminecobalt (III) chloride

(b) pentaamminechloridocobalt (III) chloride

(c) potassium hexacyanoferrate (III)

(d) potassium trioxalatoferrate (III)

(e) potassium tetrachloridoplatinum (II)

(f) diamminechlorido (methylamine) platinum(II) chloride.

Page No. 254

Answer.5

Outer electronic configuration of nickel (Z = 28) in ground state is 3d84s2. Nickel in this

complex is in + 2 oxidation state. It achieves + 2 oxidation state by the loss of the two

4s-electrons. The resulting Ni2+ ion has outer electronic configuration of 3d8. Since CN–

ion is a strong field, under its attacking influence, two unpaired electrons in the 3d

orbitals pair up.

Outer electronic configuration of nickel (Z = 28) in ground state is 3d84s2 Nickel in this

complex is in + 2 oxidation state. Nickel achieves + 2 oxidation state by the loss of two

4s-electrons. The resulting Ni2+ ion has outer electronic configuration of 3d8. Since CP

ion is a weak field ligand, it is not in a position to cause electron pairing.

Answer.6



Answer.7

Answer.8

Answer.9

Answer.10

Mn(II) ion has 3d5 configuration. In the presence of H

ligands, the distribution of these five electrons is

unpaired to form a high spin complex. However, in the presence of CN

strong field ligands, the distribution of these electrons is

contain paired electrons while the third t

complex formed is a low spin complex.

Page No.256

Answer.11

Overall stability constant (β4) = 2.1 x 1013.

Thus, the overall dissociation constant is

NCERT EXERCISES

Page No.258

Answer.1

The main postulates of Werner’s theory of coordination compounds are as follows:

(a)Metals possess two types of valences called

(i) primary valency which are ionisable; (ii) secondary valency which are non

(b)Primary valency is satisfied by the negative ions and it is that which a metal exhibits

in the formation of its simple salts.

(c)Secondary valences are satisfied by neutral ligand or negative ligand and are those

which metal exercises in the formation of its complex ions. Ev

number of secondary valences which are directed in space about central metal ion in

configuration. In the presence of H2O molecules acting as weak field

distribution of these five electrons is t32ge

2g i. e., all the electrons remain

unpaired to form a high spin complex. However, in the presence of CN

strong field ligands, the distribution of these electrons is t52ge

0g i.e., two t

ain paired electrons while the third t2g orbital contains one unpaired electron. The

complex formed is a low spin complex.

Overall stability constant (β4) = 2.1 x 1013.

Thus, the overall dissociation constant is


(a)Metals possess two types of valences called

(i) primary valency which are ionisable; (ii) secondary valency which are non

satisfied by the negative ions and it is that which a metal exhibits

in the formation of its simple salts.


which metal exercises in the formation of its complex ions. Every cation has a fixed


O molecules acting as weak field

i. e., all the electrons remain

unpaired to form a high spin complex. However, in the presence of CN– acting as

i.e., two t2g orbitals

orbital contains one unpaired electron. The


(i) primary valency which are ionisable; (ii) secondary valency which are non- ionisable

satisfied by the negative ions and it is that which a metal exhibits


ery cation has a fixed


certain fixed directions, e.g. In CoCl

valences and valences between Co and NH3

ammonia molecules linked to Co by secondary valences are directed to six corners of a

regular octahedron and thus account for structure of COCl

In modern theory, it is now referred as coordination number of central metal atom

ion.

Answer.2

When FeSO4 and (NH4)2SO4 solutions are mixed in 1: 1 molar ratio, a double salt known

as Mohr’s salt is formed. It has the formula FeSO

solution, the salt dissociates as:

The solution gives the tests for all

when CuSO4 and NH3 are mixed in the molar ratio of 1: 4 in solution, a complex

[Cu(NH3)4]SO4 is formed. Since the Cu

in square bracket), it will not give th

Answer.3

Coordination entity: It constitutes of a central atom/ion bonded to fixed number of

ions or molecules by coordinate bonds

e.g. [COCl3(NH3)3], [Ni (CO)4] etc.

Ligand: The ions/molecules bound to central atom/ion in coordination entity are called

ligands. Ligands in above examples are C

Coordination number: This is the number of bonds formed by central atom/ion with

ligands.

Coordination polyhedron: Spatial a

complex. E.g. Co and Ni polyhedron are octahedral and tetrahedral in [CoCl3

and [Ni(CO)4] respectively.

Homoleptic: Metal is bound to only one kind of ligands e

Heteroleptic: Metal is bound to more than one kind of ligand

In CoCl3-6NH3, valences between Co and Cl are primary

valences and valences between Co and NH3 are secondary. In COCl


regular octahedron and thus account for structure of COCl3-6NH3 as follows:

In modern theory, it is now referred as coordination number of central metal atom

solutions are mixed in 1: 1 molar ratio, a double salt known

as Mohr’s salt is formed. It has the formula FeSO4. (NH4)2SO4.6H2O. In aqueous

solution, the salt dissociates as:

The solution gives the tests for all the ions including Fe2+ ions. On the other hand,

are mixed in the molar ratio of 1: 4 in solution, a complex

is formed. Since the Cu2+ ions are a part of the complex entity (enclosed

in square bracket), it will not give their characteristic tests as are given by Fe

: It constitutes of a central atom/ion bonded to fixed number of

ions or molecules by coordinate bonds

] etc.

The ions/molecules bound to central atom/ion in coordination entity are called

ligands. Ligands in above examples are Cl, NH3, CO

: This is the number of bonds formed by central atom/ion with

Spatial arrangement of ligands defining the shape of

Co and Ni polyhedron are octahedral and tetrahedral in [CoCl3

Metal is bound to only one kind of ligands e.g. Ni in[Ni(CO)

und to more than one kind of ligands e.g. Coin [CoCl

, valences between Co and Cl are primary

are secondary. In COCl3-6NH3, six


as follows:

In modern theory, it is now referred as coordination number of central metal atom or

solutions are mixed in 1: 1 molar ratio, a double salt known

O. In aqueous

the ions including Fe2+ ions. On the other hand,

are mixed in the molar ratio of 1: 4 in solution, a complex

ions are a part of the complex entity (enclosed

eir characteristic tests as are given by Fe2+ ions.

: It constitutes of a central atom/ion bonded to fixed number of

The ions/molecules bound to central atom/ion in coordination entity are called

: This is the number of bonds formed by central atom/ion with

rrangement of ligands defining the shape of

Co and Ni polyhedron are octahedral and tetrahedral in [CoCl3 (NH3)3]

Ni in[Ni(CO)4]

Coin [CoCl3(NH3)3]

Answer.4

Unidentate ligand: A molecule or an ion which has only one donor atom to form one

coordinate bond with the central metal atom is called unidentate ligand, e.g. Cl- and

NH3.

Bidentate ligand: A molecule or ion which contains two donor atoms and hence forms

two coordinate bonds with the central metal atom is called a Bidentate ligand.

Ambidentate ligand: A molecule or an ion which contains two donor atoms but only

one of them forms a coordinate bond at a time with the central metal atom is called

Answer.5

Answer.6

(a) [Zn(OH)4]2-

(b) [Pt(NH3)6]4+

(c) K2[PdCl4]

(d) [Cu(Br)4]2-

(e) [CO(NH3)6](SO4)3

(f) K2[Ni(CN)4]

(g) K3[Cr(OX)3]

(h) [CO(NH3)5ONO]2+

(i) [Pt(NH3)2Cl2]

(j) [CO(NH3)5NO2]2+

Answer.7

(i) Hexamminecobalt (III) chloride.

(ii) Diamminechlorido (methylamine) platinum (II) chloride.

(iii) Hexaaquatitanium (III) ion.

(iv) Tetraamminechloridonitrito

(v)Hexaaquamanganese (II) ion.

(vi)Tetrachloridonickelate (II) ion.

(vii)Hexaamminenickel (II) chloride.

(viii)Tris (ethane -1,2-diamine) cobalt (III) ion.

(ix) Tetra carbonyl nickel (0).

Page No.259

Answer.13

Aqueous CuS04 solution exists as [Cu(H

[Cu(H20)4]2+ ions.

(i) When KF is added, the weak H

ions which is a green precipitate.

(ii)When KCl is added, Cl– ligands replace the weak H

which has bright green colour.

Answer.14

First cupric cyanide is formed which decomposes to give cuprous cyanide and

cyanogen gas. Cuprous cyanide dissolves in excess of potassium cyanide to form the

complex, K3[Cu(CN)4],

Thus, coordination entity formed in the above reaction is [Cu(CN)4]3

strong ligand, the complex ion is highly stable and does not dissociate/ionize to give

Cu2+ ions. Hence, no precipitate,with H

(iii) Hexaaquatitanium (III) ion.

(iv) Tetraamminechloridonitrito-N-cobalt (IV) chloride.

(v)Hexaaquamanganese (II) ion.

(II) ion.

(vii)Hexaamminenickel (II) chloride.

diamine) cobalt (III) ion.

solution exists as [Cu(H20)4]S04 which has blue colour due to

KF is added, the weak H20 ligands are replaced by F– ligands forming [C

ions which is a green precipitate.

ligands replace the weak H20 ligands forming [CuCl

which has bright green colour.

c cyanide is formed which decomposes to give cuprous cyanide and


Thus, coordination entity formed in the above reaction is [Cu(CN)4]3

trong ligand, the complex ion is highly stable and does not dissociate/ionize to give

ions. Hence, no precipitate,with H2S is formed.

which has blue colour due to

ligands forming [CuF4]2-

0 ligands forming [CuCl4]2- ion

c cyanide is formed which decomposes to give cuprous cyanide and


Thus, coordination entity formed in the above reaction is [Cu(CN)4]3-. As CN– is a

trong ligand, the complex ion is highly stable and does not dissociate/ionize to give

Answer.15

Answer.16

Answer.17

The crystal field splitting, ∆0, depends upon the field produced by the ligand and

charge on the metal ion. Some ligands are able to produce strong fields in which, the

splitting will be large whereas others produce weak fields and consequently result in

small splitting of d-orbitals. In general, ligands can be arranged in a series in the order

of increasing field strength as given below :

Answer.18

When the ligands approach a transition metal ion, the d

one with lower energy and the other with higher energy. The difference of energy

between the two sets of orbitals is called crystal field splitting energy (Δ0

octahedral field). If Δ0 < P (pairing energy), the fourth electron enters

one of the e°g, orbitals giving the

complexes. Such ligands for which Δ0

fourth electron pairs up in one of the t

t42ge1g thereby forming low spin complexes. Su

strong field ligands.

∆0, depends upon the field produced by the ligand and



orbitals. In general, ligands can be arranged in a series in the order

of increasing field strength as given below :

When the ligands approach a transition metal ion, the d-orbitals split into two sets,

and the other with higher energy. The difference of energy

between the two sets of orbitals is called crystal field splitting energy (Δ0

< P (pairing energy), the fourth electron enters

, orbitals giving the configuration t32ge

1g, thus forming high spin

which Δ0 < P are called weak field ligands. If Δ0

fourth electron pairs up in one of the t2g orbitals giving the configuration

thereby forming low spin complexes. Such ligands for which Δ0> P are called

∆0, depends upon the field produced by the ligand and



orbitals. In general, ligands can be arranged in a series in the order

orbitals split into two sets,

and the other with higher energy. The difference of energy

between the two sets of orbitals is called crystal field splitting energy (Δ0 for

< P (pairing energy), the fourth electron enters

, thus forming high spin

< P are called weak field ligands. If Δ0 > P, the

orbitals giving the configuration

ch ligands for which Δ0> P are called

Answer.19

Answer.20

In [Ni(H20)6]2+, Ni is in + 2 oxidation state and having 3d

which there are two unpaired electrons which do not pair in the presence of the wea

H20 ligand. Hence, it is coloured. The d

complementary light emitted is green.

In [Ni(CN)4]2- Ni is also in + 2 oxidation state and having 3d8

But in presence of strong ligand CN

up. Thus, there is no unpaired electron present. Hence, it is colourless.

Answer.21

In both the complexes, Fe is in + 2 oxidation state with d6 configuration. This means

that it has four unpaired electrons.Both CN

ligands occupy different relative positions in the spectrochemical series. They differ in

crystal field splitting energy (∆

to different wavelengths/frequencies fr

the transmitted colours are also different. This means that the complexes have

different colours in solutions.

, Ni is in + 2 oxidation state and having 3d8 electronic configuration, in

which there are two unpaired electrons which do not pair in the presence of the wea

0 ligand. Hence, it is coloured. The d-d transition absorbs red light and the

complementary light emitted is green.

Ni is also in + 2 oxidation state and having 3d8 electronic configuration.

But in presence of strong ligand CN– the two unpaired electrons in the 3d orbitals pair



that it has four unpaired electrons.Both CN– ion and H2O molecules which act as


∆0). Quite obviously, they absorb radiations corresponding

to different wavelengths/frequencies from the visible region of light. (VIBGYOR) and


.

electronic configuration, in

which there are two unpaired electrons which do not pair in the presence of the weak

d transition absorbs red light and the

electronic configuration.

npaired electrons in the 3d orbitals pair



O molecules which act as


). Quite obviously, they absorb radiations corresponding

om the visible region of light. (VIBGYOR) and


Answer.22

In metal carbonyl, the metal carbon bond (M

character. The bond are formed by overlap of atomic orbital of metal with that of C

atom of carbon monoxide in following sequence:

(a)σ -bond is first formed between metal and carbon when a vacant d

atom overlaps with an orbital containing

monoxide (: C = O:)

(b)In addition to σ -bond in metal carbonyl, the electrons from filled d

transition metal atom/ ion are back donated into anti bonding π

monoxide. This stabilises the metal ligand bonding. The above two concepts are shown

in following figure:

Answer.23

(i) K3[Co(C2O4)3] =>[CO(C204)3]

number is also 6 as C2042- is didentate. Co+3 is a case in which all elec

(ii) cis – [Cr(en)2Cl2]+ Cl–

x + 0—2 =+1

Oxidation state, x =+3

Coordination number is 6 as ‘en’ is didentate. Cr

(iii) (NH4)2[COF4] = (NH4)22+[COF4]

x —4 =—2.

Oxidation state, x = + 2

Coordination number=4.

Co2+ is a d5 case, paramagnetic

(iv)[Mn(H20)6]2+S042-

x+0f+2

.•. Oxidation state, x- + 2

Coordination number is 6.

Mn+2 is a d5 case, paramagnetic

Answer.24

(i) K[Cr(H20)2(C204)2|-3H20

In metal carbonyl, the metal carbon bond (M – C) possess both the σ and π

character. The bond are formed by overlap of atomic orbital of metal with that of C

atom of carbon monoxide in following sequence:

bond is first formed between metal and carbon when a vacant d

atom overlaps with an orbital containing lone pair of electrons on C

bond in metal carbonyl, the electrons from filled d

transition metal atom/ ion are back donated into anti bonding π-orbitals of carbon

ses the metal ligand bonding. The above two concepts are shown

)3]3-. x + 3 (-2) = -3. Oxidation state, x=+3 Coordination

is didentate. Co+3 is a case in which all elec

Coordination number is 6 as ‘en’ is didentate. Cr3+ is a cfi case, paramagnetic.

] = (NH4)22+[COF4]2-

case, paramagnetic

case, paramagnetic

3H20

C) possess both the σ and π -bond

character. The bond are formed by overlap of atomic orbital of metal with that of C-

bond is first formed between metal and carbon when a vacant d-orbital of metal

lone pair of electrons on C-atom of carbon

bond in metal carbonyl, the electrons from filled d-orbitals of a

orbitals of carbon

ses the metal ligand bonding. The above two concepts are shown

3. Oxidation state, x=+3 Coordination

is didentate. Co+3 is a case in which all electrons are paired

is a cfi case, paramagnetic.

IUPAC name is potassiumdiaquadioxalatochromate (III) hydrate.

Coordination number = 6

Oxidation state of Cr: x + 0 + 2 (-2) = – 1

.‘. x = + 3

Shape is octahedral Electronic configuration of Cr3+ = 3d3=t32ge

°g .

Magnetic moment,

μ=√n(n+2=√3×5=√15BM

= 3-87 BM

(ii) [Co(NH3)5CIlCl2IUPAC name is pentaamminechloridocobalt (III) chloride

Coordination number of Co = 6 Shape is octahedral.

Oxidation state of Co, x + 0 -1 = + 2 .’. x = + 3

Electronic configuration of Co3+ = 3d6 = t62ge°g n=0, μ =0 .

(iii) CrCI3(Py)3. IUPAC name istrichloridotripyridine chromium (III).

Answer.25

Formation of a complex in solution is an equilibrium reaction. It may be represented as

M+4L⇌ML4

The equilibrium constant of this reaction is the measure of stability of the complex.

Hence the equilibrium constant is also called as stability constant or Instability

constant may be defined as equilibrium constant for reverse reaction. The formation

of above complex may also be written in successive steps:

Stability constant is written as

β4=K1K2K3K4.

Greater the stability constant, stronger is the metal-ligand bond.

The stability of complex will depend on

(a)nature of metal

(b)Oxidation state of metal

(c)Nature of ligand e g. chelating ligand form stabler complexes

(d)Greater the basic strength of the ligand, more will be the stability.

Answeer.26

When a didentate or a polydentate ligand contains donor atoms positioned in such a

way that when they coordinate with the central metal ion, a five or a six membered

ring is formed, the effect is called chelate effect. For example,

Answer.28

Coordination number of cobalt = 6

Hence, the complex is [Co (NH3)6] Cl2. It ionizes in the solution as follows :

Thus, three ions are produced. Hence, the correct option is (iii)

Answer.29

The oxidation states are: Cr (III), Fe (II) and Zn (II).

Electronic configuration of Cr3+ = 3d3, unpaired electron = 3

Electronic configuration of Fe2+ = 3d6, unpaired electron = 4

Electronic configuration ofZn2+ = 3d10, unpaired electrons = 0

μ=√n(n+2)

where V is number of unpaired electrons Hence, (ii) has highest value of magnetic

moment.

Answer.30

Page No. 260

Answer.31

In each of the given complex, Fe is in + 3 oxidation state. As C2042-is didentate chelating

ligand, it forms chelate rings and hence (iii) out of complexes given above is the most

stable complex.

Answer.32

As metal ion is fixed, the increasing field strengths, i.e., the CFSE values of the ligands

from the Spectro-chemical series are in the order: H20<NH3< NO2–;

Thus, the energies absorbed for excitation will be in the order:

Class- XII Chemistry Chapter-9 Coordination...

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