Synthesis and characterization of compounds containing discrete tetranuclear clusters and extended arrays of molybdenum atoms

摘要

Improved synthetic pathways to the Mo(,4)Cl(,8)L(,4) cluster compounds were elucidated which provide a facile entrance to the synthesis of new four metal atom clusters. The new tetranuclear clusters, with the stoichiometry R(,4)Mo(,4)Cl(,12) (R = Et(,4)N, Pr(,4)N, O(,4)P), were prepared by the reaction of tetraalkylammonium or tetraphenylphosphonium chlorides with the rectangular tetrameric cluster Mo(,4)Cl(,8)L(,4);One electron oxidation of Mo(,4)Cl(,12)(\u274-) by I(,2) or dichlorophenyliodine yielded the Mo(,4)Cl(,12)(\u273-) cluster anion, which was shown to exist as two geometric isomers, both of which are fragments of the larger hexa- nuclear cluster anion Mo(,6)Cl(,14)(\u272-). The metal atoms in (Et(,4)N)(,3)Mo(,4)Cl(,12) form an opened tetrahedron or \u22butterfly\u22. In O(,4)P (,3)Mo(,4)Cl(,12), Pr(,4)N (,3)- Mo(,4)Cl(,12), and O(,4)As (,2) Et(,4)N Mo(,4)Cl(,12) the metal atoms form a planar rhomboidal cluster unit. Bond distances in both cluster units are indicative of strong metal-metal bonding. The reasons for the adop- tion of one configuration over the other are not completely clear, but extended Huckel calculations have shown that Jahn-Teller dis- tortions are responsible for the observation of a planar rhomboidal rather than square cluster geometry for the planar units. Magnetic susceptibility and electron paramagnetic resonance studies of O(,4)P (,3)Mo(,4)Cl(,12) and Pr(,4)N (,3)Mo(,4)Cl(,12) are consistent with the assign- ment of one unparied electron, delocalized over the cluster unit;The ternary molybdenum oxide, Sn(,0.9)Mo(,4)O(,6), was synthesized by high temperature reactions in sealed molybdenum tubes. The struc- ture of this compound is dominated by metal-metal bonded octa- hedal clusters which are fused on trans edges to form infinite chains through the lattice. Four such clusters are interconnected to form a tetragonal tunnel occupied by Sn. The short Sn-Sn distance along the channel, (2.836 (ANGSTROM)), is suggestive of Sn-Sn bonding which was also indicated by extended Huckel calculations. Disorder observed along the channel where the Sn atom resides is believed to be a consequence of the Sn-Sn bonding and the non-stoichiometry observed for the compound. Resistivity studies show the compound;is metallic. The compound exhibits weak, temperature independent paramagnetism; (\u271)DOE Report IS-T-1176. This work was performed in part under contract W-7405-eng-82 with the Department of Energy and in part under a grant (CHE-8406822) from the National Science Foundation.