Di(tert-butyl)phosphate complexes of aluminum:: Precursors to aluminum phosphate xerogels and thin films

Reactions of HO(O)P((OBu)-Bu-t)(z) with Al2Me6 and [Al((OPr)-Pr-i)(3)](4) gave the new molecular aluminum phosphate complexes [Me2AlO2P((OBu)-Bu-t)(2)](2) (1) and [Al((OPr)-Pr-i)(2)O2P((OBu)-Bu-t)(2)](4) (2), respectively. In the solid state, 1 exists as a centrosymmetric dimer consisting of two four-coordinate Al centers bridged by two phosphate groups. In the solid state 2 exists as a centrosymmetric tetramer in which the unique half of the tetramer consists of two aluminum atoms bridged by two di(tert-butyl)phosphate groups. The central part of the molecule contains a planar Al2O2 four-membered ring containing two symmetry-related Al(1) atoms bridged by two -(OPr)-Pr-i ligands. Solution-phase thermolyses of 1 and 2 in organic solvents led to the formation of transparent and opaque xerogels, respectively, after air-drying. The xerogel derived from 1 in 2-propanol had a surface area of 442 m(2) g(-1) after calcination to 600 degrees C in air. Thin, transparent films of aluminum phosphate were prepared by chemical vapor deposition (CVD) using both 1 and 2 as molecular precursors.