THEORETICAL INVESTIGATION OF ELECTRONIC STRUCTURE AND BONDING IN MOLYBDENUM FACE-BRIDGED OCTAHEDRAL CLUSTERS WITH Π-DONOR LIGANDS

Abstract

Extended Hückel Molecular Orbital (EHMO) calculations were carried out on octahedral transition metal clusters with general formula [M6X8 i Y6 a ] (M = Molybdenum; X and Y = π-Donor Ligands) in order to rationalize their electronic structure. In these species the optimal metallic electron (ME) count is of 24 but for many clusters experimentally synthesized, the ME count can vary from 20 to 48 without dramatically altering the architecture of the octahedral cluster. Herein are reported the geometrical parameters and electronic properties, of a series of clusters with 20 to 24 valence electrons per cluster. The calculated characteristics for all the considered structures are in excellent agreement with the experimental ones and requires to learn more about the relationships that exist between their structural arrangement and electronic properties especially the number of electrons available for metal-metal bonding in M6 octahedral clusters. Introduction Transition metal clusters exhibit a wide range of nuclearity with intriguing structural diversity [1-6]. Considerable attention attracted to the cluster compounds is caused by their remarkable properties and great technological application in many fields [7-10]. Systematic efforts aimed at understanding the electronic structure and bonding of these compounds have been initiated by several research groups by developing topological electron counting theories [3, 11-13]. The first Octahedral transition metal clusters with general formula [M6L8 i L6 a ] (i = inner, a = apical, relatively to Shäfer and Schnering notation) [14], have been a subject of extensive investigations because of their very interesting properties [15-21]. Such compounds are built up from M6L14 units (M = transition metal, L = halogen, chalcogen) in which the M6 cluster is face-capped by eight inner ligands (L i) and six apical ligands (L a) lie in terminal positions (see Fig. 1).