Coordination Compounds

Coordination compounds means formation of coordinate bond.

A covalent bond is formed when one one electron from both atoms are shared

A ⬤ ⬤ B → A-B

Coordinate bond is formed when only an atom/ molecules shares electron pair.

A: B → A → B

Metals first lose their electrons and create vacancies so that elements with lone pairs can come and donate.

ligands are those elements who have lone pair of electrons and donates to metals and form coordination compound.

Q1Write the formulas for the following coordination compounds:

(a) Tetraammineaquachloridocobalt(III) chloride

(b) Potassium tetrahydroxidozincate(II)

(d) Dichloridobis(ethane-1,2-diamine)cobalt(III)

(e) Tetracarbonylnickel(0)

(a) [Co(NH3)4(H2O)Cl] Cl2

(b) K2 [Zn(OH)4]

(d) [CoCl2(en)2 ] +

(e) [Ni(CO)4 ]

Q2 Write the IUPAC names of the following coordination compounds:

(a) [Pt(NH3)2Cl(NO2)]

(b) K3[Cr(C2O4)3]

(d) [Co(NH3 )5(CO3)]Cl

(e) Hg[Co(SCN)4]

(a) Diamminechloridonitrito-N-platinum(II)

(b) Potassium trioxalatochromate(III)

(d) Pentaamminecarbonatocobalt(III) chloride

(e) Mercury (I) tetrathiocyanato-S-cobaltate(III)

Q9.1 Write the formulas for the following coordination compounds:

(i) Tetraamminediaquacobalt(III) chloride

(ii) Potassium tetracyanidonickelate(II)

(iii) Tris(ethane–1,2–diamine) chromium(III) chloride

(iv) Amminebromidochloridonitrito-N-platinate(II)

(v) Dichloridobis(ethane–1,2–diamine)platinum(IV) nitrate (vi) Iron(III) hexacyanidoferrate(II)

Q9.2 Write the IUPAC names of the following coordination compounds:

(i) [Co(NH3)6]Cl2

(ii) [Co(NH3)5Cl]Cl2

(iii) K3[Fe(CN)6]

(iv) K3[Fe(C2O4)3 ]

(v) K2[PdCl4 ]

(vi) [Pt(NH3)2Cl(NH2CH3)]Cl

Ans.

(i) Hexamminecobalt(III) chloride

(ii) Pentaamminechhloridocobalt(III) chloride

(iii) Potassium hexacyanoferrate(III)

(iv) Potassium trioxalatoferrate (III)

(v) Potassium tetrachloridopalladate (II)

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

Example 9.4 Why is geometrical isomerism not possible in tetrahedral complexes having two different types of unidentate ligands coordinated with the central metal ion ?

Ans.Tetrahedral complexes do not show geometrical isomerism because the relative positions of the unidentate ligands attached to the central metal atom are the same with respect to each other.

Example 9.5 Draw structures of geometrical isomers of [Fe(NH3)2(CN)2]-

Example 9.6 Out of the following two coordination entities which is chiral (optically active)?

(a) cis-[CrCl2(ox)2]3-

(b) trans-[CrCl2(ox)2]3-

9.3 Indicate the types of isomerism exhibited by the following complexes and draw the structures for these isomers:

(i) K[Cr(H2O)2(C2O4)2]

(ii) [Co(en)3]Cl3

(iii) [Co(NH3)5(NO2)](NO3)2]

(iv) [Pt(NH3)(H2O)Cl2]

(i) Both Optical and Geometrical isomers of K[Cr(H2O)2(C2O4)2]

(ii) Optical isomers of [Co(en)3]Cl3: -

(iii) [Co(NH3)5(NO2)] (NO3)2 : The given compound can exhibit ionisation isomerism and linkage isomerism due to the presence of ambidentate ligand

Ionisation isomers:

[Co(NH3)5(NO2)] (NO3)2 [Co(NH3)5(NO3)] (NO3)(NO2)

Linkage isomers:

[Co(NH3)5(NO2)] (NO3)2 [Co(NH3)5(ONO)] (NO3)2

(iv) [Pt(NH3)(H2O)Cl2]

9.4 Give evidence that [Co(NH3)5Cl]SO4 and [Co(NH3)5(SO4)]Cl are ionisation isomers.

Ans. The ionisation isomers dissolve in water to yield different ions and thus

react differently to various reagents:

[Co(NH3)5Br]SO4 + Ba2+ → BaSO4 (s)

[Co(NH3)5SO4]Br + Ba2+ → No reaction

[Co(NH3)5Br]SO4 + Ag+ → No reaction

[Co(NH3)5SO4]Br + Ag+ → AgBr (s)

Example 9.7 The spin only magnetic moment of [MnBr4]2- is 5.9 BM. Predict the geometry of the complex ion ?

Ans. Since the coordination number of Mn2+ ion in the complex ion is 4, it will be either tetrahedral (sp3 hybridisation) or square planar (dsp2 hybridisation). But the fact that the magnetic moment of the complex ion is 5.9 BM, it should be tetrahedral in shape rather than square planar because of the presence of five unpaired electrons in the d orbitals.

Q9.5 Explain on the basis of valence bond theory that [Ni(CN)4 ] 2– ion with square planar structure is diamagnetic and the [NiCl4 ] 2– ion with tetrahedral geometry is paramagnetic.

Ans.

Q9.6 [NiCl4 ] 2– is paramagnetic while [Ni(CO)4 ] is diamagnetic though both are tetrahedral. Why?

Ans. Due to a difference in the nature of ligands. Cl- is a weak field ligand and it does not cause the pairing of unpaired 3d electrons.

Q9.7 [Fe(H2O)6 ] 3+ is strongly paramagnetic whereas [Fe(CN)6 ] 3– is weakly paramagnetic. Explain.

Ans. The hybridisation involved is d2sp3 forming inner orbital complex which is weakly paramagnetic. In present to H2O (a weak ligand), 3d-electrons do not pair up. The hydridisation involved is sp3d2 forming an outer orbital complex. As it contains five unpaired electrons, it is strongly paramagnetic.

Q9.7 Explain [Co(NH3 )6 ] 3+ is an inner orbital complex whereas [Ni(NH3 )6 ] 2+ is an outer orbital complex.

Q9.9 Predict the number of unpaired electrons in the square planar [Pt(CN)4 ] 2– ion

Ans. No unpaired electron.

Q9.10 The hexaquo manganese(II) ion contains five unpaired electrons, while the hexacyanoion contains only one unpaired electron. Explain using Crystal Field Theory.

Ans.

Mn(II) has an electronic configuration of 3d5 4s0. In the case of hexaaquomanganese (II) ion the ligand attached to metal is water which is a weak field ligand and is not able to pair up the electrons of 3d subshell and the configuration is t2g3 and eg2.

Whereas in the case of hexacyano ion the CN- is a strong field ligand and it causes pairing of electrons in the d orbitals and hence thee exist only one unpaired electron in t2g5 eg0 .

Q24 Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex:

a. K[Cr(H2O)2(C2O4)2].3H2O

b. CrCl3(py)3

c. K4[Mn(CN)6]

d. [Co(NH3)Cl]Cl2

e. Cs[FeCl4]

Q25. What is meant by stability of a coordination compound in solution? State the factor which govern stability of complexes.

Ans.

Q 26 What is meant by chelate effect? Explain briefly?

Ans.

Q27. Discuss briefly giving an example in each case the role of coordination compounds in

a. biological systems, b. analytical chemistry, c. medicinal chemistry, d. extraction/ metallurgy of metals.

Ans.

Q9.28 How many ions are produced from the complex Co(NH3)6Cl2 in the solution

(i) 6 (ii) 4 (iii) 3 (iv) 2

Ans. (iii) 3 ions

Q9.29 Amongst the following ions which one has the highest magnetic moment value?

(i) [Cr(H2O)6}3+ (ii) [Fe(H2O)6}2+ (iii) [Zn(H2O)6}2+

Ans.

(i) [Cr(H2O)6}3+ : 3d3: 3 unpaired electrons

(ii) [Fe(H2O)6}2+ : 3d6: 4 unpaired electrons, it has maximum magnetic moment

(iii) [Zn(H2O)6}2+ : 3d10: 0 unpaired electrons and is diamagnetic

Q9.30 The oxidation number of cobalt in K [ Co(CO)4] is

a. +1, b. +3, c. -1, d. -3

Ans. c. -1

x+1=0

x=-1

Q9.31 Amongst the following, the most stable complex is

(i) [Fe(H2O)6}3+ (ii) [Fe(NH3)6}3+ (iii) [Fe(C2O4)3}3- (iii) [FeCl6}3-

Ans. [Fe(C2O4)3}3- is a metal chelate. Hence, it is most stable.

Q9.32 What will be the correct order for the wavelengths of absorption in the visible region for the following: [Ni(NO2)6]4-, [Ni(NH3)6}2+, [Ni(H2O)6}2+

Ans. In the spectrochemical series the increasing order of ligand field strength is,

H2O < NH3 < NO2

Increasing order of energy is

[Ni(H2O)6}2+ < [Ni(NH3)6}2+ <[Ni(NO2)6]4-

The decreasing order of wavelength will be

[Ni(H2O)6}2+ > [Ni(NH3)6}2+ > [Ni(NO2)6]4-