Select the correct statement(s): (1) Order of energies of...

Select the correct statement(s): (1) Order of energies of $d$-orbitals of metal ion in a square planar complex is: $$ d_{x}^{2}-y^{2}>d_{x y}>d_{z}^{2}>d_{z x}=d_{y z} $$ (2) The CFSE of $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Br}_{3}$ is $-2.4 \Delta_{0}$ (3) The magnitude of CFSE in octahedral field depends on nature of the ligand. (4) When $\mathrm{NH}_{3}$ is added to $\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$, its magnetic moment does not charge.

Select the correct statement(s):
(1) Order of energies of $d$-orbitals of metal ion in a square planar complex is:
$$
d_{x}^{2}-y^{2}>d_{x y}>d_{z}^{2}>d_{z x}=d_{y z}
$$
(2) The CFSE of $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Br}_{3}$ is $-2.4 \Delta_{0}$
(3) The magnitude of CFSE in octahedral field depends on nature of the ligand.
(4) When $\mathrm{NH}_{3}$ is added to $\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$, its magnetic moment does not charge.

Key Concepts

Magnetic Properties of Coordination Complexes

The magnetic moment of a coordination complex is determined by the number of unpaired electrons in the d-orbitals after splitting. Changes in ligand identity and geometry can alter the spin state (high-spin vs low-spin) and consequently the magnetic properties such as magnetic moment. This concept is particularly important when analyzing how ligand substitution might influence the spin state and magnetic behavior of a complex.

Crystal Field Stabilization Energy (CFSE)

CFSE is the stabilization energy that results from the electronic arrangement in the split d-orbitals of a metal ion compared to a hypothetical situation where all five d-orbitals are degenerate. Its magnitude depends on the distribution of electrons in the lower and higher energy levels and is influenced by the geometry of the complex as well as the strength of the ligand field. CFSE plays a significant role in determining the stability, reactivity, and structure of coordination compounds.

Ligand Field Strength and Spectrochemical Series

Ligands cause varying degrees of splitting in the d-orbitals based on their field strength, which is ordered by the spectrochemical series. Strong field ligands produce a larger splitting energy (?) and can lead to low-spin configurations, while weak field ligands cause a smaller splitting and usually result in high-spin configurations. Understanding this concept is critical for interpreting phenomena such as changes in magnetic properties and colors in different coordination complexes.

d-Orbital Splitting Patterns

In coordination complexes, the d-orbitals split into groups of higher and lower energy levels depending on the geometry of the ligand field. For example, in an octahedral field, the d-orbitals split into eg and t2g sets, whereas in a square planar geometry the splitting is more complex. These patterns are essential for predicting the distribution of electrons among the d-orbitals and, consequently, the physical and chemical properties of the metal complex.

Crystal Field Theory

Crystal Field Theory (CFT) explains how the approach of ligands around a metal ion causes the degeneracy of its d-orbitals to be lifted, leading to different energy levels depending on the spatial orientation of the orbitals relative to the ligands. This theory is foundational in understanding the electronic structure, bonding, colors, and magnetic properties of coordination complexes.

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