THE SYNTHESIS AND CRYSTAL-STRUCTURES OF THE RELATED SERIES OF ALUMINOBORATES - CO2.1AL0.9BO5, NI2ALBO5, AND CU2ALBO5

We report on the growth of single crystals of Ni2AlBO5, Cu2AlBO5, and the mixed-valent Co2.1Al0.9BO5 from borax fluxes. All of these materials have been studied by single-crystal X-ray diffraction. The nickel and cobalt compounds are isostructural with the natural mineral ludwigite, while the copper compound is a monoclinically distorted variant of this structure. All three compounds show nonrandom disorder of the transition metal and aluminium atoms over four crystallographically distinct metal sites. We discuss the structural effects of this disorder and attempt to rationalize the observed occupancies on the basis of covalent and ionic forces. Ni2AlBO5: orthorhombic,a = 12.013(1)Å,b = 9.111(1)Å,c = 2.942(1)Å, space groupPbam,Z = 4, R = 4.07%. Co2.1Al0.9BO5: orthorhombic,a = 12.010(2)Å,b = 9.197(2)Å,c = 2.993(1)Å, space groupPbam,Z = 4, R = 4.44%. Cu2AlBO5: monoclinic,a = 9.365(1)Å,b = 11.778(2)Å,c = 3.072(2)Å, β = 97.71(2)°, space groupP21a, Z = 4, R = 4.59%. © 1990 Academic Press, Inc.