Group III quinaldates: synthesis, structure and photoluminescence

The reactions of Al(III), Ga(III) and In(III) nitrates with 2-quinaldic acid (qaH) afforded [Al2(OH)2(qa)4]·2H2O (1), [Ga(qa)2(H2O)2]NO3 (2) and [In(qa)2(NO3)(H2O)] (3), respectively, in high yields. The crystal structures of 1, 2 and 3 have been determined by single-crystal X-ray crystallography. The structure of 1 features a di-hydroxo bridged [Al2(μ-OH)2]4+ dimer in which each Al(III) is further ligated by two bidentate chelate qa ligands. Complexes 2 and 3 are mononuclear with the M(III) ions in octahedral environments surrounded by two bidentate chelate qa and two H2O in 2 or one H2O and a terminal NO3 in 3. Characteristic IR as well as thermal analysis and solid-state fluorescence are discussed.