Synthesis, Crystal Structure, and Electrical and Magnetic Characterizations of the Monoclinic Compounds LnMoSiO (Ln = La, Ce, Pr, and Nd; = 0 and 0.35) Containing Mo Clusters and Mo Dimers.

Powder samples of the new monoclinic compounds LnMoSiO (Ln = La, Ce, Pr, and Nd) and single crystals of PrMoSiO were obtained by the solid-state reaction. The crystal structure of PrMoSiO was determined by single-crystal X-ray diffraction. PrMoSiO crystallizes in the monoclinic space group 2/ with unit-cell parameters = 5.6361 (2) Å, = 17.5814 (8) Å, = 10.9883 (4) Å, and = 4. Full-matrix least-squares refinement on using 7544 independent reflections for 203 refinable parameters results in = 0.0359 and w = 0.0831. The structure contains chains of MoO clusters and chains of edge-sharing MoO octahedra with alternately short (2.508 Å) and long (3.161 Å) Mo-Mo distances running parallel to the axis that are separated by 8- or 10-coordinate Pr-O polyhedra. Magnetic susceptibility measurements on the LnMoSiO (Ln = La, Ce, Pr, and Nd) are in agreement with a trivalent state of the rare earths for the Ce, Pr, and Nd compounds, while that on the lanthanum compound confirms the presence of one unpaired electron per Mo as expected. Resistivity measurements on a single crystal show that PrMoSiO is a small band gap semi-conductor.