Preparation and Crystal Structures of the Ternary Compounds Ag2SiP2 and AuSiP

The title compounds were prepared by solid state reaction of the elemental components. Their crystal structures were determined from single-crystal X-ray diffractometer data. Ag2SiP2: 142d, a = 652.75(5) pm, c = 855.0(1) pm, Z = 4, R = 0.024 for 611 structure factors and 14 variable parameters; AuSiP: R3m, a = 345.9(1) pm, c = 1720.0(3) pm, Z = 3, R = 0.023 (352 F values, 11 variables). The silicon atoms in Ag2SiP2 are tetrahedrally coordinated by phosphorus atoms. The compound might therefore be considered as a phosphidosilicate and its formula can be rationalized as (Ag+l)2Si+4(P_3)2. However, Ag2SiP2 is not a tetrahedral compound since the phosphorus atoms have five near neighbors (3Ag + 2Si) and the silver atoms are coordinated by three phosphorus atoms in almost trigonal planar coordination. Weak silver-silver bonding is assumed for the shortest Ag-Ag contacts of 318 pm. In AuSiP the gold atoms are in a linear coordination of one silicon (235.5 pm) and one phosphorus atom (232.6 pm). The silicon and phosphorus atoms are tetrahedrally coordinated (3Si + 1 Au and 3P + 1 Au, respectively). Thus, the elements can be assigned oxidation numbers according to the formula Au+lSi+2P-3 . This structure was also refined in the centrosymmetric space group R3m, but in this improper setting the silicon and phosphorus atoms occupy one crystallographic site with random occupancy.