Understanding Nickel Complex Magnetic Behavior

The complex NiCl₂{P(C₂H₅)₂(C₆H₅)}₂ shows temperature-dependent magnetic behavior due to different coordination geometries adopted by Ni²⁺.

Step 1: Analyze the Ligand

The ligand P(C₂H₅)₂(C₆H₅) is a phosphine with moderate steric bulk. It can facilitate both tetrahedral and square planar geometries.

Step 2: Nickel(II) Electronic Configuration

Ni²⁺ has the electron configuration: ${\left[\mathrm{Ar}\right]}^{3d^8}$

Step 3: Geometry and Magnetic Properties

Tetrahedral geometry: High-spin configuration with two unpaired electrons → Paramagnetic

Square planar geometry: Low-spin configuration with all electrons paired → Diamagnetic

Step 4: Temperature Dependence

At higher temperatures: Tetrahedral geometry predominates (paramagnetic)

At lower temperatures: Square planar geometry becomes stable (diamagnetic)

Final Answer

The coordination geometries are respectively: tetrahedral (paramagnetic) and square planar (diamagnetic)

Related Concepts

Crystal Field Theory: Explains how ligand fields split d-orbitals, affecting electron pairing.

Jahn-Teller Effect: Some complexes distort from ideal geometry to lower energy.

Spin Crossover: Some compounds switch between high-spin and low-spin states with temperature.

Key Formulae

Magnetic moment for octahedral/tetrahedral complexes: $\mu =\sqrt{n(n+2)}\text{ BM}$

Where n = number of unpaired electrons

For square planar d⁸ systems: μ ≈ 0 BM (diamagnetic)

For tetrahedral d⁸ systems: μ ≈ 2.8-3.2 BM (paramagnetic)