Synthesis, structural studies, and physical properties of the RE5Mo32O54 (RE= La, Ce, Pr, Nd) compounds containing trans-Bicapped Mo-8 octahedral clusters and Mo-7-Mo-10-Mo-7 triclusters

摘要

Polycrystalline samples and single crystals of the RE5Mo32O54 compounds (R = La, Ce, Pr, and Nd) were synthesized by solid state reactions at high temperature in sealed Mo crucibles. Their crystal structures were determined by single crystal X-ray diffraction methods. All four compounds are isostructural and crystallize in the monoclinic P2(l)/c space group. Their crystal structure exhibits two different cluster types: an isolated bicapped octahedral Mo-8 cluster having an isomeric trans form and a Mo-24 chain fragment that can be described as Mo-7-Mo-10-Mo-7 triclusters. The oxygen atoms bridge all Mo-Mo edges or are linked to free apices. Both Mo8O24 and Mo24O60 cluster units are arranged in layers parallel to the ac plane. These compounds show semiconducting behavior with activation energies of about 0.06 eV and room temperature resistivities in the range 0.04-0.08 Omega(.)cm. The magnetic susceptibility data reveal a magnetic moment of 1.77 mu(B) localized on the Mo sublattice in addition to that arising from the rare-earth ions. (C) 2000 Academic Press. [References: 42]