SYNTHESIS AND X-RAY CRYSTAL-STRUCTURE OF THE NEW NONSTOICHIOMETRIC PHASE RB0.60NA6.25GA20.02

The structure of a crystal with the composition Rb//0//. //6//0Na//6//. //2//5Ga//2//0//. //0//2 has been determined using single crystal diffractometry. The space group is Fmmm with lattice parameters a equals 25. 086(5), b equals 46. 036(17), and c equals 16. 043(3) Angstrom. Diffraction data with 4 less than equivalent to 2 theta less than equivalent to 50 degree (MoK alpha radiation) were collected on a Nonius CAD4 diffractometer within the octant hkl. The structure was solved by trial methods and refined by full-matrix least-squares to a final R(F) equals 0. 080 for 1150 independent reflections with I greater than 3 sigma (I). The structure of Rb//0//. //6//0Na//6//. //2//5Ga//2//0//. //0//2 contains gallium icosahedra and 'double-icosahedral' clusters (21 gallium atoms). Such polyhedra have already been encountered in Li//3Na//5Ga//1//9//. //5//6 structure.