Synthesis and structural characterization of the alkaline earth aryloxide aggregates H2Ba8(.mu.5-O)2(OPh)14(HMPA)6 and H2Sr6Ba2(.mu.5-O)2(OPh)14(HMPA)6. A new structural type displaying metal ion site selectivity

Abstract

The interest in the formation and chemistry of main group alkoxides and aryloxides has undergone a renaissance over the last few years. There are many reasons for this surge of interest in such compounds, many of which until recently were poorly characterized or not known at all. One such stimulus is the discovery of superconducting ceramics containing alkaline earth ions. The reaction of barium metal granules with phenol and hexamethylphosphoramide (HMPA) in toluene at 25[degrees]C yields a novel eight-metal atom aggregate. The reaction of Sr[sub 3](OPh)[sub 6](HMPA)[sub 5] with barium metal and phenol yields a structurally related species. The two aggregates have been characterized by IR and [sup 1]H, [sup 13]C, and [sup 31]P[l brace][sup 1]H[r brace] NMR spectroscopy and single-crystal X-ray studies and shown to consist to two square-based pyramidal M[sub 5]([mu][sub 5]-O) fragments sharing a common basal edge. The structure is completed by [mu][sub 3]- and [mu][sub 2]-phenoxide and terminal HMPA ligands. The selectivity for barium in the two polyhedral sites where the square-based pyramids are joined originates in the higher coordination number there. 20 refs., 2 figs., 3 tabs.