What is the structure of anionic coordination sphere in $[Cr(NH_3)_6][CuCl_5]$ complex?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Trigonal bipyramidal
In the coordination complex $[Cr(NH_3)_6][CuCl_5]$, the formula consists of a cationic coordination sphere and an anionic coordination sphere.
1. Identifying the Anionic Sphere
The complex dissociates as follows:
$[Cr(NH_3)_6][CuCl_5] \rightarrow [Cr(NH_3)_6]^{3+} + [CuCl_5]^{3-}$
The anionic coordination sphere is the $[CuCl_5]^{3-}$ ion.
2. Determining the Structure
For a coordination number of 5 (where the metal is bonded to five ligands), the two common geometries are Trigonal bipyramidal and Square pyramidal.
In the specific case of the $[CuCl_5]^{3-}$ ion within this complex:
- The Copper ($Cu^{2+}$) ion has a $d^9$ electronic configuration.
- The $[CuCl_5]^{3-}$ anion is a classic example used in textbooks to illustrate the Trigonal bipyramidal geometry.
- In this geometry, the five chloride ligands are arranged such that three are in an equatorial plane (forming a triangle) and two are at the axial positions (above and below the plane).