The crystal structures of the strontium gallates Sr10Ga6O19 and Sr3Ga2O6

The crystal structures of Sr10Ga6O19 and Sr3Ga2O6 have been characterized using X-ray diffraction techniques. In the case of Sr10Ga6O19, the structure was determined from a single crystal diffraction data set collected at room conditions and refined to a final R index of 0.061 for 3471 observed reflections (I > 2 sigma (I)). The compound is monoclinic with space group C12/c1 (a = 34.973(4) Angstrom, b = 7.934(1) Angstrom, c = 15.943(2) Angstrom, = 103.55(1)degrees, V = 4300.7(6) Angstrom (3), Z = 8, D-calc = 4.94 g/cm(3), mu (MoK alpha) = 32.04 mm(-1)) and can be classified as an oligogallate. It is the first example of an inorganic compound where six [TO4]-tetrahedra of only one chemical species occupying the tetrahedral centres are linked via bridging oxygen atoms to form [T6O19] groups. The hexamers are not linear, but highly puckered. Eleven symmetrically different Sr cations located in planes parallel (100) crosslink between the oligo-groups. They are coordinated by six to eight oxygen ligands. The structure of Sr3Ga2O6 has been refined from powder diffraction data using the Rietveld method (space group Pa (3) over bar, a = 16.1049(1), V = 4177.1(1) Angstrom (3), Z = 24, D-calc = 4.75 g/cm(3)). The compound is isostructural with tricalcium aluminate and contains highly puckered, six-membered [Ga6O18](18-) rings. The rings are linked by strontium cations having six to nine nearest oxygen neighbors. (C) 2001 Academic Press.