The First Ternary Phase in the Ga-Sn-Pd System: Synthesis, Crystal Structure, and Catalytic Properties of Ga2+x+ySn4-xPd9

The new ternary compound Ga2+x+ySn4-xPd9 (x = 0.72, y = 0.06) was synthesized by arc melting of the elements. The crystal structure was solved from the single-crystal X-ray diffraction data [space group Fd<(3)overbar>m, a = 12.4048(9) angstrom, Z = 8, 222 reflections, R-F = 0.035]. The crystal structure of Ga2+x+ySn4-xPd9 is related to the Ti2Ni type and its filled derivatives (eta-phases) with additional Pd atoms at octahedrally and tetrahedrally coordinated sites. The electronic density of states of Ga2+x+ySn4-xPd9 is similar to those of the binary compounds GaPd and GaPd2, which are catalytically active in the semihydrogenation of acetylene. Quantum-chemical calculations revealed a distribution of the electron localizability indicator analogous to that for GaPd in a system of heteroatomic electron-deficient two-center interactions. In contrast to the arrangement in GaPd, the spatial organization of these interactions hinders the formation of isolated active sites on the surface and results in a relatively low catalytic activity for Ga2+x+ySn4-xPd9.