THE CRYSTAL-STRUCTURE OF (AL0,5GA0,5)CUOA SO4 - COPPER INTERMEDIATE BETWEEN PLANAR AND CLOSED COORDINATION

Single crystals of the new oxide arsenate (Al0,5Ga0,5)CuOAsO4 (monocli nic, P2(1)/c, a = 734.3(2)pm, b = 1024.79(9) pm, c = 563.4(2) pm, beta = 99.93(1)degrees, Z = 4) were obtained by reaction of Al/As/Cu/Ga-al loys with oxygen. The crystal structure was determined from four-circl e diffractometer data (w2R = 0.039 for 1211 F-2 values and 76 paramete rs). The structure contains [Cu2O6] double squares arranged in slabs p erpendicular to the a axis such that a [4 + 1]-coordination of the cop per atoms by oxygen atoms results which is intermediate between square -planar and square-pyramidal. Along [100] layers of corner sharing (Al /Ga)O-4 and AsO4 tetrahedra are alternating with buckled Cu layers.