Q23. The standard potential E0cell for a cell reaction given below is +0.7 V. The standard reaction free energy ΔrG° for this cell is _______Kj mol-1 (correct up to two decimal places). (Given: Faraday constant,
( F = 96,500 C mo-1)
Au3+(aq) + 3Ag(s) -> Au(s) + 3Ag+(aq)
The complex [PtBr(NH₃)(py)₂]Br, a square planar platinum(II) coordination compound, exhibits 2 geometrical isomers. Platinum has an atomic number of 78, and with +2 oxidation state and coordination number 4, it adopts square planar geometry. Pyridine (py) acts as a neutral monodentate ligand, like NH₃, while Br⁻ is inside the coordination sphere, with one Br⁻ as counter ion outside.
Complex Structure
The coordination sphere is [PtBr(NH₃)(py)₂]⁺, featuring four ligands: one Br, one NH₃, and two identical py ligands around Pt(II). This Ma₂bc formula in square planar geometry allows cis-trans isomerism due to positions of the unique ligands (NH₃ and Br). The two py ligands occupy remaining positions.
Possible Isomers
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Cis isomer: NH₃ and Br are adjacent (90° apart), with py ligands also adjacent.
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Trans isomer: NH₃ and Br are opposite (180° apart), with py ligands adjacent to both.
No optical isomers exist, as square planar complexes have a plane of symmetry. Thus, total geometrical isomers: 2.
Detailed Explanation
In square planar [Ma₂bc], fixing the two identical ‘a’ (py) ligands creates two arrangements for ‘b’ (NH₃) and ‘c’ (Br): adjacent or opposite. Adjacent positions yield the cis form; opposite yield trans. No further geometrical variants due to identical py. Counter ion Br⁻ does not affect inner sphere geometry.
| Isomer Type | Ligand Positions Relative to Pt | Description |
|---|---|---|
| Cis | NH₃ and Br at 90° | Py ligands adjacent |
| Trans | NH₃ and Br at 180° | Py ligands adjacent to each |
The geometrical isomers [PtBr(NH₃)(py)₂]Br topic is key for CSIR NET Life Sciences aspirants studying coordination chemistry. This square planar Pt(II) complex, with pyridine (py) and atomic number 78 for Pt, shows exactly 2 geometrical isomers due to cis-trans arrangements.
Geometrical Isomers Breakdown: In [PtBr(NH₃)(py)₂]⁺, two identical py enable cis (adjacent NH₃-Br) and trans (opposite) forms. No optical activity in square planar geometry. Ideal for exam questions on stereoisomerism.
