Gallium(III) organophosphate adducts with the bidentate amines 2,2'-dipyridyl and 1,10-phenanthroline

A number of gallium(III) organophosphonates form adducts with the bidentate amines 2,2'-bipyridyl and 1,10-phenanthroline. These adducts contain a 1:2:1 molar ratio of metal/phosphorus/amine and have the proposed formulations Ga(O3PR)(O2P(OH)R)(C10H8N2)·H2O and Ga(O3PR)(O2P(OH)R)(C12H8N2)·H2O (where R=CH3, C6H5 and CH2C6H5; C10H8N2 is 2,2'-bipyridyl and C12H8N2 is 1,10-phenanthroline). Unlike the parent gallium(III) organophosphonates, which conform to the general formula Ga(OH)(O3PR)·xH2O (x=0 or 1), the amine adducts lack the hydroxo group, but contain the organophosphonate ligand in the partially as well as fully deprotonated forms. All compounds were isolated from aqueous solutions as monohydrates, with the exception of the bipyridyl adduct of gallium(III) phenylphosphonate, which is anhydrous. TGA measurements suggest that for the hydrates, the water molecule is not coordinated to the metal. The bipyridyl adducts of gallium(III) phenylphosphonate and gallium(III) methylphosphonate, like the parent gallium(III) organophosphonates, are very likely layered, as indicated by the powder XRD patterns. In contrast, the corresponding phenanthroline adducts are non-layered, and both the bipyridyl and phenanthroline adducts of gallium(III) benzylphosphonate are amorphous solids. FTIR, powder XRD, TGA, XPS, solid state 31P/13C MAS-NMR and BET surface area data are presented and discussed.