5.2 Application and Limitation of Valence Bond Theory

  Coordination Compounds

    1.0 Basics
    2.0 Addition Salt
    3.0 Nomenclature of Co-ordination Compounds
    4.0 Werner's Co-ordination Theory
    5.0 Valence bond theory
    6.0 Crystal field splitting theory (CFST)
    7.0 Effective atomic number
    8.0 Magnetic Moment
    9.0 Application of Crystal Field Splitting Theory (CFST)
    10.0 Isomerism in Co-ordination compounds
    11.0 Organo-metallic compounds
    12.0 Stability of Co-ordination compounds

---

5.2 Application and Limitation of Valence Bond Theory

S.No.	Complex	Configuration of metal ion	Central metal atom	Hybridization	Geometry of Complex	Number of unpaired electron	Magnetic behaviour
1	${\left[ {Ti{{({H_2}O)}_6}} \right]^{ + 3}}$	${d^1}$	$T{i^{ + 3}}$	${d^2}s{p^3}$	OCTAHEDRAL	1	PARAMAGNETIC
2	${\left[ {V{{({H_2}O)}_6}} \right]^{ + 3}}$	${d^2}$	${V^{ + 3}}$	${d^2}s{p^3}$	OCTAHEDRAL	2	PARAMAGNETIC
3	${\left[ {Cr{{({H_2}O)}_6}} \right]^{ + 3}}$	${d^3}$	$C{r^{ + 3}}$	${d^2}s{p^3}$	OCTAHEDRAL	3	PARAMAGNETIC
4	${\left[ {Cr{{(N{H_3})}_6}} \right]^{ + 3}}$	${d^3}$	$C{r^{ + 3}}$	${d^2}s{p^3}$	OCTAHEDRAL	3	PARAMAGNETIC
5	${\left[ {Mn{F_6}} \right]^{3 - }}$	${d^4}$	$,M{n^{ + 3}}$	$s{p^3}{d^2}$	OCTAHEDRAL	4	PARAMAGNETIC
6	${\left[ {Mn{{(CN)}_6}} \right]^{3 - }}$	${d^4}$	$,M{n^{ + 3}}$	${d^2}s{p^3}$	OCTAHEDRAL	2	PARAMAGNETIC
7	${\left[ {MnC{l_4}} \right]^{2 - }}$	${d^5}$	$M{n^{ + 2}}$	$s{p^3}$	TETRAHEDRAL	5	PARAMAGNETIC
8	${\left[ {Fe{F_6}} \right]^{ - 3}}$	${d^5}$	$F{e^{ + 3}}$	$s{p^3}{d^2}$	OCTAHEDRAL	5	PARAMAGNETIC
9	${\left[ {Fe{{({H_2}O)}_6}} \right]^{ + 3}}$	${d^5}$	$F{e^{ + 3}}$	$s{p^3}{d^2}$	OCTAHEDRAL	5	PARAMAGNETIC
10	${\left[ {Fe{{(CN)}_6}} \right]^{ - 3}}$	${d^5}$	$F{e^{ + 3}}$	${d^2}s{p^3}$	OCTAHEDRAL	1	PARAMAGNETIC
11	${\left[ {Fe{{(CN)}_6}} \right]^{ - 4}},$	${d^6}$	$F{e^{ + 2}},$	${d^2}s{p^3}$	OCTAHEDRAL	0	DIAMAGNETIC
12	${\left[ {FeC{l_4}} \right]^{2 - }}$	${d^6}$	$F{e^{ + 2}},$	$s{p^3}$	TETRAHEDRAL	4	PARAMAGNETIC
13	${\left[ {Co{{(N{H_3})}_6}} \right]^{ + 3}}$	${d^6}$	$C{o^{ + 3}}$	${d^2}s{p^3}$	OCTAHEDRAL	0	PARAMAGNETIC
14	${\left[ {Co{F_6}} \right]^{ - 3}}$	${d^6}$	$C{o^{ + 3}}$	$s{p^3}{d^2}$	OCTAHEDRAL	4	DIAMAGNETIC
15	$Ni{(CO)_4}$	$3{d^6}4{s^2}$	$Ni$	$s{p^3}$	TETRAHEDRAL	0	DIAMAGNETIC
16	${\left[ {Ni{{(CN)}_4}} \right]^{2 - }}$	${d^8}$	$N{i^{ + 2}}$	$ds{p^2}$	SQUARE PLANAR	0	DIAMAGNETIC
17	${\left[ {NiC{l_4}} \right]^{ + 2}}$	${d^8}$	$N{i^{ + 2}}	$s{p^3}$	TETRAHEDRAL	2	PARAMAGNETIC
18	${\left[ {Ni{{({H_2}O)}_6}} \right]^{2 + }}$	${d^8}$	$N{i^{ + 2}}	$s{p^3}{d^2}$	OCTAHEDRAL	2	PARAMAGNETIC
19	${\left[ {CuC{l_4}} \right]^{ - 2}}$	${d^9}$	$C{u^{ + 2}}$	$s{p^3}$	TETRAHEDRAL	1	PARAMAGNETIC
20	${\left[ {Zn{{(N{H_3})}_4}} \right]^{ + 2}}$	${d^{10}}$	$Z{n^{ + 2}}$	$s{p^3}$	TETRAHEDRAL	0	DIAMAGNETIC
21	$\left[ {Pt(N{H_3})C{l_2}} \right]$	${d^8}$	$P{t^{ + 3}}$	$ds{p^2}$	SQUARE PLANAR	0	DIAMAGNETIC

---

Limitation of valence bond theory: While the VBT theory, to larger extent, explains the formations of sturucture, magnetic behaviour of coordination compounds. It contains the following shortcomings:

1. It involves a number of assumption.

2. It does not give quantitative interpretaion of magnetic data.

3. It does not explain the colour exhibited by coordination number.

4. It does not distinguish between weak and strong ligands.

---

Example 6. ${\left[ {Cu{{(N{H_3})}_4}} \right]^{2 + }}$

Explanation: Here $C{u^{2 + }}$ is strong ligand. Hybridisation is $s{p^2}d$ with square planar geometry.

---

Special Case:

Example 7. ${\left[ {Ni{{(N{H_3})}_6}} \right]^{ + 2}}$

Explanation: Here $N{i^{2 + }}$ is a strong ligand. So, it has an unpaired electron. Hybridisation is $s{p^3}{d^2}$ with geometry octahedral complex.