Draw orbital-energy splitting diagrams and use the...

Draw orbital-energy splitting diagrams and use the spectrochemical series to show the orbital occupancy for each of the following (assuming that $\mathrm{H}_{2} \mathrm{O}$ is a weak-field ligand): $\begin{array}{llll}{\text { (a) }\left[\mathrm{MoCl}_{6}\right]^{3-}} & {\text { (b) }\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}} & {\text { (c) }\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}}\end{array}$

Key Concepts

d-Electron Count and Oxidation State

Determining the metal oxidation state and subsequently the d-electron count is fundamental for predicting the electron filling of the split d orbitals. Accurate electron counts enable the correct depiction of orbital occupancy in the crystal field splitting diagrams, thereby influencing the overall electronic structure and properties of the complex.

High-Spin and Low-Spin Configurations

High-spin and low-spin terminology describes the distribution of electrons among the split d orbitals. In a high-spin complex, electrons occupy higher energy orbitals to maximize spin multiplicity when the ligand field splitting is small, whereas in a low-spin complex, electrons pair up in the lower energy orbitals when the splitting is large, resulting from strong-field ligands.

Coordination Geometry

The shape of the complex, such as octahedral, square planar, or tetrahedral, directly influences the pattern of d orbital splitting. Each geometry has a distinct arrangement of ligand-metal interactions, leading to different energy separations among the d orbitals, which must be taken into account when constructing orbital energy diagrams.

Crystal Field Theory

Crystal Field Theory explains how the degeneracy of the metal ion d orbitals is lifted when the ion is surrounded by ligands. It provides the basis for drawing orbital-energy splitting diagrams by showing how the interactions between metal d orbitals and the electrostatic field of the ligands lead to distinct energy levels depending on the geometry of the complex.

Spectrochemical Series

The spectrochemical series is an ordering of ligands based on the strength of the crystal field splitting they induce. This series is crucial in determining whether a complex will have a high-spin or low-spin configuration, as strong-field ligands can cause a larger splitting, leading in some cases to electron pairing in the lower energy orbitals.

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