ON THE CRYSTAL-STRUCTURE OF IN3MO11O-17 A ND THE PHYSICAL-PROPERTIES OF OLIGOMERIC OXOMOLYBDATES

In3Mo11O17 is characterized by its molybdate framework Mo22O348- belon ging to the general series Mo4n+2O6n+4x- (with n = 5). The phase grows in star-like aggregates and crystallizes within the orthorhombic syst em (a = 988.0(2) pm, b = 951.2(2) pm, c = 3 176.7(4) pm). There are ol igomeric clusters built from five trans edge-sharing Mo6 octahedra, su rrounded by 0 atoms over all empty edges according to the Aufbau princ iple Mo22O18iO4/2i-iO28/2i-a. In the remaining structural channel one fin s an In68+ polycation which is geometrically equivalent with the o ne of In11Mo40O62. The Mo-O and Mo-Mo distances within the cluster are the same like in In11Mo40O62, too, but there are shorter inter cluste r distances (306 pm) in In3Mo11O17. Disorder in the structure may be u nderstood in terms of the presence of constitutional isomers. While th e electrical resistivity of PbMo5O8 resembles the one of a strongly di sturbed metal (with a local minimum around 120 K), the temperature cha racteristic of Tl0.8Sn0.6Mo7O11 is typical for a semiconductor. Oxomol ybdates with even longer oligomers like In11MoO62 and In3Mo11O17 show metallic conductivity. This course corresponds with the sizes of the c lusters and their electronic intercoupling which can be estimated from the specific lengths of the inter cluster distances. The effective ma gnetic moment grows with increasing cluster length from 0.97 mu(B) (Pb Mo5O8) to 1.40 mu(B) (In11Mo40O62) per cluster (exception: In3Mo11O17) , and so does the contribution of the temperature-independent paramagn etism (from 890 to 2191 x 10(-6) emu/mol per cluster). Thus, a single condensed octahedron carries roughly 440 x 10(-6) emu/mol as a tempera ture-independent paramagnetism, similar to the M6X12 halide clusters. In11Mo40O62 shows an interesting change in the temperature dependence of its magnetic suszeptibility.