Why is it that Ni(CN)4^2- is diamagnetic, but NiCl4^2- is paramagnetic?

Name: Problem 52, Chapter 22: Chemistry The Science in Context
Uploaded: 2020-06-21T03:00:02-08:00
Duration: 2 min 23 s
Channel: Aadit Sharma
Description: Why is it that Ni(CN)4^2- is diamagnetic, but NiCl4^2- is paramagnetic?

step 1 In the given compound, NICL4, 2 negative, the oxidation state of nickel is 2 positive. So the el

Why is it that Ni(CN)4^2- is diamagnetic, but NiCl4^2- is...

Key Concepts

Electronic Configuration and Spin States

The distribution of electrons in the d-orbitals of the metal ion determines the spin state of the complex. In a low spin configuration, electrons are paired in the lower energy orbitals, making the complex diamagnetic. In a high spin configuration, electrons occupy higher energy orbitals singly before pairing, resulting in unpaired electrons and paramagnetism. This is fundamentally determined by the crystal field splitting energy relative to the pairing energy.

Coordination Geometry

The shape of a coordination complex, such as square planar or tetrahedral, heavily influences the splitting patterns of the d-orbitals. Square planar geometries, often associated with strong field ligands, tend to favor low spin electron configurations, whereas tetrahedral geometries, commonly observed with weak field ligands, typically lead to high spin configurations. This variation in geometry is critical to understanding the differences in magnetic behavior between similar metal complexes.

Ligand Field Theory

This concept explains how the d-orbitals of a metal ion split into different energy levels when surrounded by ligands. The nature and arrangement of the ligands affect the magnitude of this splitting, which in turn influences whether the electrons pair up or remain unpaired. This theory is key to understanding the magnetic properties of coordination complexes.

Spectrochemical Series

The spectrochemical series ranks ligands based on their ability to split the d-orbitals of a central metal ion. Strong field ligands, such as cyanide, produce a large crystal field splitting that often leads to electron pairing (low spin complexes), resulting in diamagnetism. In contrast, weak field ligands like chloride cause smaller splitting, allowing electrons to remain unpaired (high spin complexes), which gives rise to paramagnetism.

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