In octahedral coordination entities, the single d electron occupies the lower energy t₂g orbital. For d⁴ ions, the fourth electron can either pair with an existing electron in the t₂g level or occupy the higher energy eg level, depending on the relative magnitudes of crystal field splitting (∆₀) and pairing energy (P).
How are electrons assigned in the d orbitals of metal ions in octahedral coordination entities, and what happens in d⁴ ions?
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In octahedral coordination entities, electrons are assigned to the d orbitals of metal ions based on the t₂g and eg sets. For d⁴ ions, there are two possible patterns of electron distribution. The fourth electron can either enter the t₂g level and pair with an existing electron, or it can avoid pairing energy by occupying the higher-energy eg level. The choice between these possibilities depends on the relative magnitudes of the crystal field splitting (∆₀) and the pairing energy (P), where P represents the energy required for electron pairing in a single orbital.