Gallium(III) complexes of aroylhydrazones derived from nicotinic acid hydrazide in solid state and in solution

•Determination of Ga(III) - aroylhydrazone binding constants by UV/Vis spectroscopy.•Analysis of complexes in solution by mass spectrometry.•Synthesis of Ga(III) - aroylhydrazones complexes.•Structural analysis of complexes in solid state by IR spectroscopy.•Comparison with analogue Fe(III) complexes. The coordination properties of N'-salicylidene-3-pyridinecarbohydrazide (H2L1), N'-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide (H2L2), N'-(2-hydroxy-4-methoxyphenylmethylidene)-3-pyridinecarbohydrazide (H2L3), and N'-(2-hydroxy-5-methoxyphenylmethylidene)-3-pyridinecarbohydrazide (H2L4) towards Ga(III) ions as mimetic for Fe(III) ions were studied in solid state and in solution by mass spectrometry, UV–vis and IR spectroscopic techniques. Binding properties were probed at different pH values and methanol/water mixture. In methanol/water 1/1 system at pH 2.52 the 1:1 and 1:2 complexes with Ga(III) were formed and corresponding stability constants were determined by UV–vis spectroscopy. Cumulative constants for Ga(III) complexes (log β2) with ligands H2L1−H2L4 amounted to 12.4, 11.5, 10.6 and 11.2 respectively, showing that additional methoxy group in meta position decreases stability of complexes. The complexes isolated from ethanolic solution had 1:2 (metal:ligand) stoichiometry. In all complexes the remaining charge of metal ion was neutralized by nitrate ions as shown by IR spectroscopy. Only for H2L2 the keto-enol tautomeric interconversion was noticed. All complexes were analyzed by mass spectrometry and fragmentation pathways were suggested for [Ga(HL)2]+, [GaL]+ and [Ga(L)(H2O)]+. The comparison with analogue Fe(III) complexes was made. It can be concluded that even though the bonds between Ga(III) and ligands are weaker than in the analogue Fe(III) complexes, Ga(III) forms stable complexes, indicating mimetic ability of Ga(III) for Fe(III). [Display omitted]