NEW NIOBIUM COMPLEXES OF ALKYNES .5. ELECTRONIC-STRUCTURE AND BONDING IN THE TETRANUCLEAR COMPLEX OF NIOBIUM [NB4OCL8((PHC)4)2]2-

Electronic structure and bonding in a newly prepared tetranuclear complex of niobium, [Nb4OClg{(PhC)4}2]2−, are discussed on the basis of molecular orbital calculations by the Fenske-Hall method. The anion consists of a planar, rectangular Nb4group with an oxygen atom at the center, and a C-shaped PhC-C(Ph)C(Ph)-CPh chain clasps each short Nb-Nb edge at the middle and lies in a plane perpendicular to the Nb4O plane. Our study has been mainly focused on the problems related to the unprecedented structural features of the anion, specifically, the Nb-Nb and Nb-O bonding, and the bonding of the C4Ph4unit to the metal atoms. The resulting bonding scheme gives a satisfactory account of the structure and is consistent with the assignment of a formal oxidation state of III to the metal atoms and the existence of strong bonds between the close pairs of metal atoms. © 1990, American Chemical Society. All rights reserved.