Question

How many geometrical isomers are possible for [Pt(Py)(NH₃)(Br)(Cl)]?

• A. 0
• B. 3
• C. 15
• D. 4

Hint:

For square planar complexes: - [Ma₂b₂]: 2 isomers (cis and trans). - [Ma₂bc]: 2 isomers (cis and trans). - [Mabcd]: 3 isomers.

Answer 1

The Correct Option is B

Concept: The complex [Pt(Py)(NH₃)(Br)(Cl)] is a coordination compound with Platinum (Pt) as the central metal ion. Key structural features: • Coordination Number: 4 (there are four monodentate ligands: Pyridine, Ammonia, Bromide, and Chloride). • Geometry: Platinum(II) complexes with a coordination number of 4 almost always adopt a square planar geometry. • Type: This follows the general formula [Mabcd], where a, b, c, and d are four different monodentate ligands.
In a square planar complex of the type [Mabcd], geometrical isomers are determined by fixing one ligand and placing the other three ligands in the position trans to it, one at a time.
Let's fix NH₃ as the reference ligand: • One isomer where Py is trans to NH₃. • One isomer where Br is trans to NH₃. • One isomer where Cl is trans to NH₃. Any other arrangement will simply be a rotation of one of these three. Therefore, there are exactly 3 geometrical isomers.
Square planar complexes rarely show optical isomerism because the molecular plane itself acts as a plane of symmetry. Thus, these 3 isomers are purely geometrical.