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) ?, b=7.934(1) ?, c=15.943(2) ?, BETA=103.55(1)°, V=4300.7(6) ?3, Z=8, Dcalc=4.94 g/cm3, MU (MoKALPHA )=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 , a=16.1049(1), V= 4177.1(1) ?3, Z=24, Dcalc=4.75 g/cm3). 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.