2,2′-Bipyridine,1,10-phenanthroline and 2,2′:6′,2″-terpyridine in gallium(III) chemistry: Complexes containing the {GaIII2(μ-OH)2}4+ core

The reactions of Ga(NO3)3 · 9H2O with 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) and 2,2′:6′,2″-terpyridine (terpy) in alcohols afford the complexes [Ga2(OH)2(bpy)4](NO3)4 (1), [Ga2(OH)2(phen)4](NO3)4 (2) and [Ga2(OH)2(H2O)2(terpy)2](NO3)4 (3), respectively, in good yields. The crystal structures of 1 · 1.3MeOH · 1.4H2O, 2 · 4.5MeOH and 3 have been solved by single-crystal X-ray crystallography. The three complexes contain the {GaIII2(μ-OH)2}4+ core. Four nitrogen atoms from two chelating bpy (1) or phen (2) complete distorted octahedral coordination at each metal centre. In 3 one tridentate chelating terpy and one aquo ligand complete six coordination at each GaIII atom. The crystal structure of 2 · 4.5MeOH is stabilized by hydrogen bonds and intermolecular π–π stacking interactions, while in 3 hydrogen bonds create a double-chain, ladder-like architecture. Characteristic IR data are discussed in terms of the nature of bonding and the structures of the three complexes. The 1H NMR spectra of complexes 2 and 3 suggest the presence of the free ligand and one solution species containing the coordinated ligand. The structure of the cation [Ca2(OH)2(bpy)4]4+ is retained in D2O as deduced by the 2D homonuclear COSY map.