SYNTHESIS AND CRYSTAL-STRUCTURE OF PBMO5O8 - A REDUCED OXOMOLYBDATE WITH MO10O28 DOUBLE OCTAHEDRA

The crystal structure of the new phase PbMo5O8 contains oligometric Mo clusters which consist of two edge-sharing Mo6 octahedra connected according to Mo10O6iO4/2i-iO16/2i-a. The compound is isotypic with LaMo5O8. Isolated, divalent Pb atoms are located in the "channels" of the monoclinic structure (a = 999.3(2) pm, b = 924.7(1) pm, c = 753.6(2) pm, beta = 109.39(2)degrees, P2(1)/a). Compared to the compound In11Mo40O62 the Mo-O distances (average 206 pm) and the Mo-Mo distances within the octahedral units (average 275 pm) are slightly decreased by 1 and 4 pm, respectively. The very short Mo-Mo distances (278 pm) between the cluster units which are not observed in In11Mo40O62 (320 pm) are due to excess electrons in these inter-cluster bonds which would otherwise occupy antibonding cluster states.