Hydrothermal synthesis of Group 13 metal trifluoride complexes with neutral N-donor ligands

Abstract

The reactions of the hydrated Group 13 fluorides, MF₃·3H₂O (M = Al, Ga or In) with 2,2′:6′,2′′-terpyridyl, 2,2′-bipyridyl or 1,10-phenanthroline under hydrothermal conditions (180 °C/15 h) produced high yields of the complexes [MF₃(terpy)]·3H₂O, [MF₃(bipy)(OH₂)]·2H₂O and [MF₃(phen)(OH₂)]. X-Ray crystal structures of [M′F₃(terpy)]·3H₂O (M′ = Al or Ga), [M′F₃(bipy)(OH₂)]·2H₂O and [GaF₃(phen)(OH₂)] show that all of them contain distorted octahedral geometries at the metal with mer-trifluoride coordination. Extensive H-bonding (F⋯H–OH) links the molecules. The complexes have been further characterised by microanalysis, IR, ¹H, ¹⁹F{¹H} and ²⁷Al NMR spectroscopy. In contrast, reactions of the trifluorides with the acyclic triamine, N,N,N′,N′,N′′-pentamethyldiethylenetriamine, under similar hydrothermal conditions results in cleavage of the triamine and ring-closure to form the 1,1,4-trimethylpiperazinium cation, [⊂Me₂N(CH₂)₂NMe(CH₂)₂]⁺, with fluorometallate anions, and confirmed by X-ray analysis of [⊂Me₂N(CH₂)₂NMe(CH₂)₂]₂[Al₂F₈(OH₂)₂]·2H₂O. The strongly H-bonded [GaF₃(terpy)]·3H₂O was also obtained by Cl/F exchange from [GaCl₃(terpy)] and [NBu₄]F or [K(2,2,2-crypt)]F. Crystallisation of a mixture of [NH₄][PF₆] and [GaF₃(terpy)]·3H₂O from aqueous solution produced the edge-bridged cationic complex, [{Ga(terpy)F}₂(μ-F)₂][PF₆]₂. The synthesis of the more sterically bulky [GaCl₃(^tBu₃-terpy)] (^tBu₃-terpy = 4,4′4′′-tris-^tBu-2,2′:6′,2′′-terpyridyl) and the crystal structure of [GaCl₂(^tBu₃-terpy)][GaCl₄], which contains a trigonal bipyramidal cation, are also reported.