Q1(d). Aluminium oxinate

Answer in brief

Oxine is 8-hydroxyquinoline; its deprotonated O,N-bidentate ligand forms neutral, six-coordinate Al(C₉H₆NO)₃.

Key points

• The phenolic oxygen loses its proton; oxygen and the quinoline nitrogen then bind the same aluminium centre, forming a five-membered chelate ring.
• Three monoanionic oxinate ligands balance Al³⁺ and provide six donor atoms in a distorted octahedral arrangement.
• The precipitation stoichiometry is Al³⁺ + 3C₉H₇NO → Al(C₉H₆NO)₃(s) + 3H⁺. Control of pH is needed because protonation suppresses ligand binding.