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

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 Sr3(OPh)6(HMPA)5 with barium metal and phenol yields a structurally related species. The two aggregates have been characterized by IR and H-1, C-13, and P-31{H-1} NMR spectroscopy and single-crystal X-ray studies and shown to consist to two square-based pyramidal M5(mu5-O) fragments sharing a common basal edge. The structure is completed by mu3- and mu2-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. Crystal data: for H2Ba8O2(OPh)14(HMPA)6.2PhMe (-172-degrees-C), a = 16.379(3) angstrom, b = 19.504(4) angstrom, c = 26.763(5) angstrom, beta = 100.90(0)-degrees with Z = 2 in space group P2(1)/n; for H2Sr6-Ba2O2(OPh) 14(HMPA)6.2PhMe (-158-degrees-C), a = 17.797(2) angstrom, b = 17.421(2) angstrom, c = 26.624(3) angstrom, beta = 107.62(0)-degrees with Z = 2 in space group P2(1)/n.