Synthesis, Crystal Structure, and Electrical and Magnetic Characterizations of the Monoclinic Compounds Ln3Mo4+xSi1–xO14(Ln = La, Ce, Pr, and Nd; x= 0 and 0.35) Containing Mo3Clusters and Mo2Dimers

Powder samples of the new monoclinic compounds Ln3Mo4SiO14(Ln = La, Ce, Pr, and Nd) and single crystals of Pr3Mo4.35Si0.65O14were obtained by the solid-state reaction. The crystal structure of Pr3Mo4.35Si0.65O14was determined by single-crystal X-ray diffraction. Pr3Mo4.35Si0.65O14crystallizes in the monoclinic space group P21/nwith unit-cell parameters a= 5.6361 (2) Å, b= 17.5814 (8) Å, c= 10.9883 (4) Å, and Z= 4. Full-matrix least-squares refinement on F2using 7544 independent reflections for 203 refinable parameters results in R1= 0.0359 and wR2= 0.0831. The structure contains chains of Mo3O13clusters and chains of edge-sharing MoO6octahedra with alternately short (2.508 Å) and long (3.161 Å) Mo–Mo distances running parallel to the aaxis that are separated by 8- or 10-coordinate Pr–O polyhedra. Magnetic susceptibility measurements on the Ln3Mo4SiO14(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 Mo3as expected. Resistivity measurements on a single crystal show that Pr3Mo4.35Si0.65O14is a small band gap semi-conductor.