Structure of SnMo5O8 containing bioctahedral Mo10 clusters

Synthesis, crystal and electronic structures, and magnetic properties of LiLn9Mo16O35 (Ln = La, Ce, Pr, and Nd) compounds containing the original cluster Mo16O36

The new compounds LiLn(9)Mo(16)O(35) (Ln=La, Ce, Pr, and Nd) were synthesized from stoichiometric mixtures of Li(2)MoO(4), Ln(2)O(3), Pr(6)O(11) or CeO(2), MoO(3), and Mo heated at 1600 °C for 48 h in a molybdenum crucible sealed under a low argon pressure. The crystal structure, determined from a single crystal of the Nd member, showed that the main building block is the Mo(16)O(36) unit, the Mo(16) core of which is totally new and results from the fusion of two bioctahedral Mo(10) clusters. It can also be viewed as a fragment of an infinite twin chain of edge-sharing Mo(6) octahedra. The Mo(16)O(36) cluster units share some oxygen atoms to form infinite chains running parallel to the b axis, which are separated by the rare-earth and lithium cations. (7)Li-NMR experiments, carried out at high field on the nonmagnetic LiLa(9)Mo(16)O(35), provided insights into the local environment of the lithium ions. Magnetic susceptibility measurements confirmed the trivalent oxidation state of the magnetic rare-earth cations and indicated the absence of localized moments on the Mo(16) clusters. The electronic structure of the LiLn(9)Mo(16)O(35) compounds was analyzed using molecular and periodic quantum calculations. The study of the molecular orbital diagrams of isolated Mo(16)O(36) models allowed the understanding of this unique metallic architecture. Periodic density functional theory calculations demonstrated that few interactions occur between the Mo(16) clusters, and predicted semiconducting properties for LiLn(9)Mo(16)O(35) as a band gap of 0.57 eV was computed for the lanthanum phase.

Synthesis, Structural Evolution, and Electrical Properties of the Novel Mo12 Cluster Compounds K1+xMo12S14 (x = 0, 1.1, 1.3, and 1.6) with a Tunnel Structure

The new structural type (1) K(2.3)Mo12S14 was prepared by solid-state reaction at 1500 degrees C in a sealed molybdenum crucible. The compound crystallizes in the trigonal space group P1c, Z = 2, (1) a = 9.1720(7) Angstroms, c = 16.403(4) Angstroms. Its crystal structure was determined from single-crystal X-ray diffraction data and consists of interconnected Mo12S14 units that form an original and unprecedented three-dimensional framework in which large tunnels are occupied randomly by a part of the K+ ions. The remaining K+ ions are localized between two consecutive Mo(12)S(14) units along the c axis. By carrying out topotactic oxydo-reduction reactions at low temperature (<100 degrees C), we were able to remove or insert K+ ions in the channels and thus form isostructural phases K(1+x)Mo12S14 (0 < or = x < or = 1.6). Thus, we have solved the crystal structures for the following three compositions: (2) K(2.1)Mo12S14, (3) KMo12S14, and (4) K(2.6)Mo12S14 ((2) a = 9.1476(4) A, c = 16.421(1) Angstroms; (3) a = 9.0797(9) Angstroms, c = 16.412(6) Angstroms; and (4) a = 9.1990(4) Angstroms, c = 16.426(4) Angstroms). Electrical resistivity measurements carried out on single crystals of K(2.3)Mo12S14 and KMo12S14 indicate that the former is semiconducting, whereas the latter is metallic. The evolution of the Mo-Mo distances with respect to the stoichiometry in potassium is discussed.