Question

Which one of the following complexes will exhibit the minimum paramagnetic behaviour?
(Atomic Number of Cr = 24, Co = 27)

1. [Cr(H2O)6]3+
2.[Cr(Cn)6]3-
3.[Co(H2O)6]3+
4.[Cof6]3-
​

Answer 1

Answer:

2. ........................

Answer 2

To find:

Which one of the following complexes will exhibit the minimum paramagnetic behaviour?

Calculation:

In order to calculate the paramagnetic behaviour in a co-ordinate complex we just need to find out the number of unpaired electrons in the central metal .

1) In [Cr(H2O)6]3+ ,

${Cr}^{ + 3} \implies \: [Ar] \: {3d}^{3} \\ \rightarrow \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: [Ar] \boxed{ \uparrow | \uparrow | \uparrow | - | - }$

So, 3 unpaired electrons.

2) In [Cr(Cn)6]3-

${Cr}^{ + 3} \implies \: [Ar] \: {3d}^{3} \\ \rightarrow \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: [Ar] \boxed{ \uparrow \downarrow| \uparrow | - | - | - }$

So, 1 unpaired electron.

3) In [Co(H2O)6]3+

${Co}^{ + 3} \implies \: [Ar] \: {3d}^{6} \\ \rightarrow \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: [Ar] \boxed{ \uparrow \downarrow| \uparrow | \uparrow| \uparrow | \uparrow}$

So, 4 unpaired electrons.

4) In [Cof6]3-

${Co}^{ + 3} \implies \: [Ar] \: {3d}^{6} \\ \rightarrow \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: [Ar] \boxed{ \uparrow \downarrow| \uparrow | \uparrow| \uparrow | \uparrow}$

So, 4 unpaired electrons.

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Since, 2) In [Cr(Cn)6]3- has lowest number of unpaired electrons, hence it will exhibit the lowest paramagnetic behaviour.

• Always remember that CN- is a strong field lig-and, hence has a tendency to pair up electrons in the central metal orbitals.