28.2.6—Coordination number and complex formula

Coordination number is the number of donor atoms directly bonded to the central metal, not always the number of ligand molecules. The complex charge is metal charge plus all ligand charges.

Choose ligands to fill the stated coordination number, then add charges algebraically. Denticity matters: one bidentate ligand occupies two sites.

A +2 metal with four neutral NH₃ ligands gives [M(NH₃)₄]²⁺; a +3 metal with two oxalate ions (2− each) gives [M(C₂O₄)₂]⁻.

Do not use ligand count as coordination number for en or EDTA, and do not confuse oxidation state with overall complex charge.