Q23.96P - Chemistry: Molecular Nature Of Matter And Change

Question

Which of these ions cannot form both high-spin and low-spin octahedral complexes: 

(a) ${\mathbf{Ti}}^{\mathbf{3}\mathbf{+}}$; (b) ${\mathbf{Co}}^{\mathbf{2}\mathbf{+}}\mathbf{;}$(c) ${\mathbf{Fe}}^{\mathbf{2}\mathbf{+}}$; (d) ${\mathbf{Cu}}^{\mathbf{2}\mathbf{+}}\mathbf{?}$

Step-by-Step Solution

Answer

${\mathrm{Ti}}^{3+}$ and ${\mathrm{Cu}}^{2+}$ cannot form both high-spin and low-spin complexes.

Step 1: Formation of octahedral complex

High-spin and low spin octahedral complexes are possible to form only when the number of d electrons is 4, 5, 6 or 7. The metal ions with 1, 2 or 3d electrons always form high-spin complexes because of no need for pairing up electrons. The metal ions with 8 or 9 d electrons will always form high-spin complexes because low energy d orbitals are filled with 6 electrons and higher energy d orbitals will have one or two unpaired electrons $\left(d^8 \text{or} d^9\right)$ .

Step 2: Electronic configuration

a) Electron configuration of ${\mathrm{Ti}}^{3+}:1 {\mathrm{s}}^{2}2 {\mathrm{s}}^{2}2{\mathrm{p}}^{6}3 {\mathrm{s}}^{2}3{\mathrm{p}}^{6}3 {\mathrm{d}}^1$; so, the ${\mathrm{Ti}}^{3+}$ metal ion can only form only high-spin octahedral complexes, because it has 1d electron.

b) Electron configuration of ${\mathrm{Co}}^{2+}:1 {\mathrm{s}}^{2}2 {\mathrm{s}}^{2}2{\mathrm{p}}^{6}3 {\mathrm{s}}^{2}3{\mathrm{p}}^{6}3 {\mathrm{d}}^7$; so, the ${\mathrm{Co}}^{2+}$metal ion can form both high-spin and low-spin octahedral complexes, because it has 7 d electrons.

c) Electron configuration for ${\mathrm{Fe}}^{2+}:1 {\mathrm{s}}^{2}2 {\mathrm{s}}^{2}2{\mathrm{p}}^{6}3 {\mathrm{s}}^{2}3{\mathrm{p}}^{6}3 {\mathrm{d}}^6;$ so, the ${\mathrm{Fe}}^{2+}$ metal ion can form both high-spin and low-spin octahedral complexes, because it has 6 d electrons.

d) Electron configuration of ${\mathrm{Cu}}^{2+}:1 {\mathrm{s}}^{2}2 {\mathrm{s}}^{2}2{\mathrm{p}}^{6}3 {\mathrm{s}}^{2}3{\mathrm{p}}^{6}3 {\mathrm{d}}^9$; so, the ${\mathrm{Cu}}^{2+}$ metal ion can form only high-spin octahedral complexes, because it has 9d electrons.