Past exam of the chemistry B course of the University of Cambridge / 2025 / Paper 2 / B6 / b / v

Both complexes contain cobalt(III), hence a $d^6$ metal ion. The approximately octahedral molecular geometry, relatively high metal oxidation state and five ammonia donors make the octahedral splitting large enough that pairing is favorable. Their low-spin configuration isAll six metal $d$ electrons are paired, and the ligands in coordination chemistry have closed shells, so neither complex has a permanent spin magnetic moment: both exhibit diamagnetism. The difference between N and O attachment is insufficient to change this low-spin assignment.