Total number of structural isomers of
[Co(NH₃)₆][Cr(CN)₆]

The coordination compound [Co(NH3)6][Cr(CN)6] consists of two distinct coordination complexes: a cobalt complex with ammonia ligands and a chromium complex with cyanide ligands. To determine the total number of structural isomers for this compound, we need to analyze each part separately, focusing on the coordination numbers, geometries, and possible arrangements of the ligands around the central metal ions.

Understanding the Components

The compound is made up of two metal centers:

• Cobalt (Co): Surrounded by six ammonia (NH3) ligands.
• Chromium (Cr): Surrounded by six cyanide (CN) ligands.

Cobalt Complex: [Co(NH3)6]

Cobalt typically exhibits an octahedral geometry when coordinated with six ligands. Since ammonia is a neutral ligand, the cobalt complex does not have any geometric isomers. Therefore, there is only one structural isomer for [Co(NH3)6], which is the octahedral arrangement of the ammonia ligands around the cobalt ion.

Chromium Complex: [Cr(CN)6]

For the chromium complex, cyanide is also a neutral ligand, and it can form different types of isomers. However, like the cobalt complex, the [Cr(CN)6] complex also adopts an octahedral geometry. The key point here is that cyanide can exhibit linkage isomerism due to its ability to coordinate through either the carbon or nitrogen atom. This means that the cyanide ligands can be arranged in two different ways:

• Carbon-bonded (C-bonded) cyanide
• Nitrogen-bonded (N-bonded) cyanide