Question

Which of the following statement(s) is/are correct regarding coordination complex?

• A. Complex compound cannot act as counter ion
• B. Ligand donates electrons to central metal ion
• C. Central metal ion accepts electrons from ligands
• D. In $K_4\left[Fe\right(CN{)}_6]$, the ionisation sphere is $\left[Fe\right(CN{)}_6{]}^{4-}$

Answer 1

Answer: (B), (C)

Central metal ion accepts electrons from ligands

Complex compound act as counter ion when there are two coordination spheres joined together by ionisation sphere.
Examples:
1. $\left[Ag\right(N{H}_3{)}_2\left]\right[Ag\left(CN{)}_2\right]$
2. $\left[Cr\right(NH3\left)6\right]\left[Co\right(CN\left)6\right]$

Generally, central metal atom/ion accept electrons from ligands. It behaves as lewis acid.

Ligands are electron-rich species which bounded to the central atom/ion inside the square bracket.

In general, ligands will donate the electron to central metal atom
and behave as lewis base.

The central atom/ion and the ligands attached to it are enclosed in a square bracket is coordination sphere.
The molecule or ionic species present outside the coordination sphere constitute the ionisation sphere.
In $K_4\left[Fe\right(CN{)}_6]$, the ionisation sphere is $K^{+}$ and the coordination sphere is $\left[Fe\right(CN{)}_6{]}^{4-}$.
Hence, options (b) and (c) are correct.