Chapter 9 Coordination Compounds Solutions
Question - 31 : - [Fe(CN)6]4− and[Fe(H2O)6]2+ areof different colours in dilute solutions. Why?
Answer - 31 : -
Thecolour of a particular coordination compound depends on the magnitude of thecrystal-field splitting energy, Δ. This CFSE in turn depends on the nature ofthe ligand. In case of [Fe(CN)6]4− and[Fe(H2O)6]2+,the colour differs because there is a difference in the CFSE. Now, CN− isa strong field ligand having a higher CFSE value as compared to the CFSE valueof water. This means that the absorption of energy for the intra d-d transitionalso differs. Hence, the transmitted colour also differs.
Question - 32 : - Discuss the nature ofbonding in metal carbonyls.
Answer - 32 : -
Themetal-carbon bonds in metal carbonyls have both σ and π characters. A σ bond isformed when the carbonyl carbon donates a lone pair of electrons to the vacantorbital of the metal. A π bond is formed by the donation of a pair of electronsfrom the filled metal d orbital into the vacant anti-bondingπ* orbital (also known as back bonding of the carbonyl group). The σ bondstrengthens the π bond and vice-versa. Thus, a synergic effect is created dueto this metal-ligand bonding. This synergic effect strengthens the bond betweenCO and the metal.
Question - 33 : - Givethe oxidation state, d-orbital occupation and coordination numberof the central metal ion in the following complexes:
Answer - 33 : -
(i) K_3[Co(C_2O_4)_3]
(ii) cis-[Cr(en)_2Cl_2]Cl
(iii) (NH_4)_2[CoF_4]
(iv) [Mn(H_2O)_6]SO_4
_
Answer
(i) K3[Co(C2O4)3]
The central metal ion is Co.
Its coordination number is 6.
The oxidation state can be given as:
x − 6 = −3
x = + 3
The d orbitaloccupation for Co3+ is t2g6eg0.
(ii) cis-[Cr(en)2Cl2]Cl
The central metal ion is Cr.
The coordination number is 6.
The oxidation state can be given as:
x + 2(0) + 2(−1) = +1
x − 2 = +1
x = +3
The d orbitaloccupation for Cr3+ is t2g3.
(iii) (NH4)2[CoF4]
The central metal ion is Co.
The coordination number is 4.
The oxidation state can be given as:
x − 4 = −2
x = + 2
The d orbitaloccupation for Co2+ is eg4 t2g3.
(iv) [Mn(H2O)6]SO4
The central metal ion is Mn.
The coordination number is 6.
The oxidation state can be given as:
x + 0 = +2
x = +2
The d orbitaloccupation for Mn is t2g3 eg2.
Question - 34 : - Write down the IUPAC name for each of thefollowing complexes and indicate the oxidation state, electronic configurationand coordination number.
Answer - 34 : -
Also give stereochemistry and magnetic moment of the complex:
(i) K[Cr(H_2O)_2(C_2O_4)_2].3H_2O
(ii) [Co(NH_3)_5Cl]Cl_2
(iii) CrCl_3(py)_3
(iv) Cs[FeCl_4]
(v) K_
4[Mn(CN)_
6]
Answer
(i) Potassium diaquadioxalatochromate (III) trihydrate.
Oxidation state of chromium = 3
Electronicconfiguration: 3d3: t2g3
Coordination number = 6
Shape: octahedral
Stereochemistry:
Magnetic moment, μ 
∼ 4BM
(ii) [Co(NH3)5Cl]Cl2
IUPAC name: Pentaamminechloridocobalt(III)chloride
Oxidation state of Co = +3
Coordination number = 6
Shape: octahedral.
Electronicconfiguration: d6: t2g6.
Stereochemistry:
Magnetic Moment = 0
(iii) CrCl3(py)3
IUPAC name: Trichloridotripyridinechromium(III)
Oxidation state of chromium = +3
Electronicconfiguration for d3 = t2g3
Coordination number = 6
Shape: octahedral.
Stereochemistry:
Both isomers are optically active. Therefore,a total of 4 isomers exist.
Magnetic moment,μ
∼ 4BM
(iv) Cs[FeCl4]
IUPAC name: Caesium tetrachloroferrate (III)
Oxidation state of Fe = +3
Electronicconfiguration of d6 = eg2t2g3
Coordination number = 4
Shape: tetrahedral
Stereochemistry: optically inactive
Magnetic moment:
μ
(v) K4[Mn(CN)6]
Potassium hexacyanomanganate(II)
Oxidation state of manganese = +2
Electronicconfiguration: d5+: t2g5
Coordination number = 6
Shape: octahedral.
Streochemistry: optically inactive
Magnetic moment,μ
What is meant bystability of a coordination compound in solution? State the factors whichgovern stability of complexes.
Answer - 35 : -
The stability of a complex in a solutionrefers to the degree of association between the two species involved in a stateof equilibrium. Stability can be expressed quantitatively in terms of stabilityconstant or formation constant.
Forthis reaction, the greater the value of the stability constant, the greater isthe proportion of ML3 in the solution.
Stability can be of two types:
(a) Thermodynamicstability:
The extent to which the complex will beformed or will be transformed into another species at the point of equilibriumis determined by thermodynamic stability.
(b) Kineticstability:
This helps in determining the speed withwhich the transformation will occur to attain the state of equilibrium.
Factors that affect the stability of a complex are:
(a) Charge on the central metal ion: Thegreaterthe charge on the central metal ion, the greater is the stability of thecomplex.
2. Basic nature ofthe ligand: A morebasic ligand will form a more stable complex.
2. Presence ofchelate rings: Chelationincreases the stability of complexes.
Question - 36 : - Whatis meant by the chelate effect? Give an example.
Answer - 36 : -
When a ligand attaches to the metal ion in amanner that forms a ring, then the metal- ligand association is found to bemore stable. In other words, we can say that complexes containing chelate ringsare more stable than complexes without rings. This is known as the chelateeffect.
For example:
Question - 37 : - Discuss briefly giving an example in eachcase the role of coordination compounds in:
Answer - 37 : -
(i) biological system
(ii) medicinal chemistry
(iii) analytical chemistry
(iv) extraction/metallurgy of metals
Answer
(i) Role of coordination compounds in biologicalsystems:
We know that photosynthesis is made possibleby the presence of the chlorophyll pigment. This pigment is a coordinationcompound of magnesium. In the human biological system, several coordinationcompounds play important roles. For example, the oxygen-carrier of blood, i.e.,haemoglobin, is a coordination compound of iron.
(ii) Role of coordination compounds in medicinalchemistry:
Certaincoordination compounds of platinum (for example, cis-platin) areused for inhibiting the growth of tumours.
(iii) Role of coordination compounds in analyticalchemistry:
During salt analysis, a number of basicradicals are detected with the help of the colour changes they exhibit withdifferent reagents. These colour changes are a result of the coordinationcompounds or complexes that the basic radicals form with different ligands.
(iii) Role of coordination compounds in extractionor metallurgy of metals:
The process ofextraction of some of the metals from their ores involves the formation ofcomplexes. For example, in aqueous solution, gold combines with cyanide ions toform [Au(CN)2]. From this solution, gold is later extractedby the addition of zinc metal.Howmany ions are produced from the complex Co(NH3)6Cl2 insolution?
(i) 6 (ii) 4 (iii) 3 (iv) 2
Answer - 38 : -
(iii) The given complex can be written as[Co(NH3)6]Cl2.
Thus, [Co(NH3)6]+ along with two Cl− ions are produced.
Question - 39 : - Amongst the following ions which one has thehighest magnetic moment value?
(i) [Cr(H2O)6]3+ (ii) [Fe(H2O)6]2+ (iii) [Zn(H2O)6]2+
Answer - 39 : -
(i) No. of unpaired electrons in [Cr(H2O)6]3+ =3
Then, μ (ii) No. of unpaired electrons in [Fe(H2O)6]2+ =4
Then, μ 
(iii) No. of unpaired electrons in [Zn(H2O)6]2+ =0
Hence,[Fe(H2O)6]2+ hasthe highest magnetic moment value.
Theoxidation number of cobalt in K[Co(CO)4] is
(i) +1 (ii) +3 (iii) −1 (iv) −3
Answer - 40 : -
option (iii) is correct.
We know that CO is a neutral ligand and Kcarries a charge of +1.
Therefore, thecomplex can be written as K+[Co(CO)4]−. Therefore, the oxidation number of Co in the givencomplex is −1.