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Ch.21 - Transition Elements and Coordination Chemistry
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Non è quello che usi tu?Cambia libro di testo
Capitolo 21, Problema 21.131a

Nickel(II) complexes with the formula NiX2L2, where X− is Cl− or N-bonded NCS− and L is the monodentate triphenylphosphine ligand P(C6H5)3, can be square planar or tetrahedral.
(a) Draw crystal field energy-level diagrams for a square planar and a tetrahedral nickel(II) complex, and show the population of the orbitals.

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Identify the electron configuration of the central metal ion, Nickel(II) (Ni2+). Nickel in its +2 oxidation state has a d8 electron configuration.
Understand the difference in geometry for square planar and tetrahedral complexes. In square planar complexes, the ligands are arranged at 90-degree angles around the central metal in the same plane. In tetrahedral complexes, the ligands are arranged at approximately 109.5 degrees in a three-dimensional structure.
Draw the crystal field splitting diagram for a square planar complex. In this geometry, the d-orbitals split into two non-degenerate orbitals (dz2 and dx2-y2) at higher energy, and three degenerate orbitals (dxy, dxz, dyz) at lower energy.
Draw the crystal field splitting diagram for a tetrahedral complex. Here, the d-orbitals split differently: two orbitals (dxy, dxz, dyz) are at lower energy, and three orbitals (dz2 and dx2-y2) are at higher energy.
Populate the orbitals with the d8 electrons of Ni2+ according to the Aufbau principle, Hund's rule, and the Pauli exclusion principle, for both square planar and tetrahedral diagrams. In square planar, fill the lower energy set first, then the higher; in tetrahedral, distribute the electrons starting from the lower energy orbitals.

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Crystal Field Theory

Crystal Field Theory (CFT) explains how the arrangement of ligands around a central metal ion affects its electronic structure and energy levels. In transition metal complexes, the presence of ligands causes the degenerate d-orbitals to split into different energy levels, which is crucial for understanding the stability and color of the complexes. The extent of this splitting varies depending on the geometry of the complex, such as square planar or tetrahedral.
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The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.

Ligand Field Splitting

Ligand Field Splitting refers to the energy difference between the split d-orbitals in a transition metal complex due to the presence of ligands. In square planar complexes, the d-orbitals split into a lower energy set (d_{x^2-y^2} and d_{xy}) and a higher energy set (d_{xz}, d_{yz}, d_{z^2}), while in tetrahedral complexes, the splitting is reversed. Understanding this concept is essential for predicting the electronic configuration and magnetic properties of the complexes.
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Strong-Field Ligands result in a large Δ and Weak-Field Ligands result in a small Δ.

Coordination Geometry

Coordination Geometry describes the spatial arrangement of ligands around a central metal ion in a complex. Nickel(II) can form complexes with different geometries, such as square planar or tetrahedral, depending on the nature of the ligands and the metal's electronic configuration. This geometry influences the crystal field splitting pattern and the overall stability of the complex, making it a key factor in the analysis of coordination compounds.
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Molecular Geometry of Coordination Complexes