Question

Thiocyanate (SCN-) has the potential to coordinate metals either via N-atom or S-atom linkage. Predict the coordination linkage (N-atom or S-atom) and geometry for Zn (II) and Cu (I). Can you please explain.

Answer 1

Answer on Question#41646-Chemistry-Inorganic Chemistry

Question

Thiocyanate (SCN-) has the potential to coordinate metals either via N-atom or S-atom linkage.

Predict the coordination linkage (N-atom or S-atom) and geometry for Zn (II) and Cu (I).

Answer

The general rule based on the experimental evidence states that class A metals (forming hard acids) tend to form N-bonded thiocyanate complexes, whereas class B metals (forming soft acids) tend to form S-bonded thiocyanate complexes.

This classification is based on the HSAB (hard and soft (Lewis) acids and bases) concept, which is also known as the Pearson acid base concept. According to it:

Since $\mathrm{Cu^{+}}$ is a class B metal (forming soft acid), it forms S-bonded thiocyanate: $\mathrm{Cu - S - C\equiv N}$ $\mathrm{Zn^{2 + }}$ is a borderline acid, so it forms both S-bonded and N-bonded thiocyanates:

$\mathrm{N}\equiv \mathrm{C} - \mathrm{S} - \mathrm{Zn} - \mathrm{S} - \mathrm{C}\equiv \mathrm{N}$

$\mathrm{S = C = N - Zn - N = C = S}$

$\mathrm{S = C = N - Zn - S - C\equiv N}$

Geometry of thiocyanate ion, whatever resonance structure (N≡C-S or S=C=N), is linear, and geometry around the atom bonded to the metal is bent due to the lone pair of electrons on N and two lone pairs on S:

http://www.AssignmentExpert.com/