IGNOU BCHCT 137 2026 - Six-coordinate d9 complexes of copper (+2) show pronounced tetrag

Question

Six-coordinate d⁹ complexes of copper (+2) show pronounced tetragonal distortions. High-spin d⁴ (e.g., Cr²⁺ and Mn³⁺ and low-spin d⁷ six-coordinate complexes (e.g. Co²⁺ and Ni³⁺) may show a similar distortion, but complexes of these ions are less common, and the distortions are less pronounced than those in copper (+2). Why?

10 Jan 2026

Answer :

Word Count : 254

The pronounced tetragonal distortion observed in six-coordinate Cu²⁺ complexes can be primarily explained by the Jahn-Teller effect, which occurs when a non-linear complex has degenerate electronic states that can lower their energy through geometrical distortion. In Cu²⁺, which has a d⁹ configuration, the eg orbitals (dz² and dx²–y²) are unevenly occupied with one electron in the dx²–y² orbital and two electrons in the dz² orbital in an octahedral field. This electronic degeneracy in the eg level leads to elongation

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