Q23. Is the total number of possible geometrical isomer(s) for [PtBrCl(NH₃)(py)]⁰
is __________.

The square planar complex [PtBr(NH₃)py]²⁺ exhibits exactly 2 geometrical isomers. Pt(II) adopts square planar geometry due to its d⁸ configuration, with ligands NH₃ (neutral), py (neutral), and two Br⁻ anions balancing the +2 charge.

Complex Geometry

Platinum(II) complexes with coordination number 4 are square planar, enabling cis-trans (geometrical) isomerism when ligands differ. The formula type Ma₂bc (M=Pt, a=Br, b=NH₃, c=py) limits isomers to positions where the unique ligands (NH₃, py) are either adjacent (cis, 90°) or opposite (trans, 180°). No optical isomers occur due to the symmetry plane.

Isomer Structures

• Cis isomer: NH₃ and py occupy adjacent positions, Br ligands also adjacent. Structure: Pt with Br at 1 o’clock and 7 o’clock, NH₃ at 5 o’clock, py at 11 o’clock (or equivalent).
• Trans isomer: NH₃ and py occupy opposite positions, Br ligands adjacent. Structure: NH₃ at 12 o’clock, py at 6 o’clock, Br at 3 o’clock and 9 o’clock (or equivalent).

Thus, total geometrical isomers: 2.

Why Only Two?

Fix one Br at position 1. The second Br goes to position 2 (cis to first Br) or 3 (trans, but square planar positions are 1-2 cis, 1-3 trans). Remaining positions filled by NH₃ and py yield distinct cis/trans for the b-c pair. Ma₂bc square planar always gives 2 isomers; all ligands different (Mabcd) gives 3.

CSIR NET Introduction

In coordination chemistry for CSIR NET life sciences, understanding geometrical isomers [PtBr(NH₃)py]²⁺ is crucial. This square planar Pt(II) complex (py=pyridine) features two identical Br ligands, NH₃, and py, yielding exactly 2 geometrical isomers. Explore cis-trans arrangements, why no optical isomers exist, and exam-solving tips.

Ligand Roles and Charge

Pt²⁺ coordinates neutral NH₃ and py (C₅H₅N), plus two Br⁻ for neutrality in [PtBr(NH₃)py]²⁺. Atomic number of Pt (78) confirms d⁸ square planar geometry, standard for such complexes.

Drawing Geometrical Isomers

• Cis-[PtBr(NH₃)py]²⁺: Adjacent NH₃-py (90°), higher dipole moment.
• Trans-[PtBr(NH₃)py]²⁺: Opposite NH₃-py (180°), lower dipole moment.

No further isomers; Ma₂bc type restricts to these.

Exam Relevance for CSIR NET

CSIR NET questions test isomer counting: Ma₂b₂ → 3 isomers, Mabcd → 3, Ma₂bc → 2. Practice distinguishes from tetrahedral (no geo isomers here).