SURVEY OF THE BONDING IN SEVERAL STRUCTURAL TYPES OF TRINUCLEAR MOLYBDENUM AND TUNGSTEN CLUSTER COMPOUNDS
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The bonding within equilateral triangular clusters of molybdenum and tungsten and the bonding of -O, -O, and -Cl to them have been examined by using nonempirical Fenske-Hall calculations. Calculations on the bipyramidal and trigonal-prismatic metal-oxygen core species [Mo3(3-O)2]8+ and [Mo3(-O)6] indicate that both capping and edge bridging cause the movement of charge out of the main metal-metal bonding orbitals, resulting in the occupation of higher lying nonbonding and antibonding metal-metal orbitals. The electronic structure of the pyramidal fragment [Mo3(3-O)(-O)3]4+ is shown to be dominated by the influence of the three edge-bridging -O groups. The ability of the trinuclear framework to accommodate a variable number of electrons has been investigated by comparative calculations on [Mo3(3-O)(-O)3]4+ and [Mo3(3-O)(-Cl)3]5+, as representatives of the pyramidal type, with six and eight electrons, respectively. The results presented are consistent with the generally longer M-M bonds in systems containing the M3(3-O)2 core relative to those containing the M3(3-O)(-O)3. 1982, American Chemical Society. All rights reserved.