Bonding Analysis in Inorganic Transition-Metal Cubic Clusters. 3. Metal-Centered Tetracapped M9(μ5-E)4Ln Species with a Tetragonal Distortion

Abstract

A number of main group element (E)−transition metal (M) cluster compunds based upon a hexacapped M8 cube have been reported in two configurations: empty and with interstitial metal atoms in the center of the cube. Related molecules arise upon slow oxidation of the reaction product that forms when [Bi2Co4(CO)11]- is treated with Mo(CO)3(toluene) giving Bi−Co clusters based upon tetragonally distorted tetracapped cubic metal arrays with interstitial metal atoms. These compounds formulated as [PPN]2[Bi4Co9(CO)16]·2THF ([PPN]2[1]·2THF) and [PPN]2[Bi8Co14(CO)20]·1.08THF([PPN]2[2]·1.08THF) have been characterized via single-crystal X-ray diffraction. An alternative description ascribes the metal cores to close-packed arrays based upon the cuboctahedron. The complexes are electron rich via conventional electron-counting formalisms. To understand these molecules more fully, a thorough theoretical analysis of compounds [1]2- and [2]2- was undertaken. The calculations indicate that the bonding of the interstitial metal atom with the metallic host somewhat differs from that found in their related metal-centered cubic species M9(μ4-E)6L8, due to stretching along the 4-fold axis. The HOMO−LUMO region is slightly antibonding between the Coi atoms (i = interstitial) and the surrounding Bi and Cop (p = peripheral) atoms. As with other members of this cubic cluster class, no HOMO−LUMO gaps are observed. The actual electron counts for [1]2- and [2]2-, however, favor stronger Cop−Coi and Bi−Coi bonding than would be observed for the allowed higher electron counts. Crystallographic data for [PPN]2[1]·2THF: triclinic space group P1̄; a = 13.560(5), b = 15.893(5), c =11.884(4) Å; α = 105.26(2), β = 98.25(3), γ = 83.25(3)°; Z = 1. Crystallographic data for [PPN]2[2]·1.08THF: triclinic space group P1̄; a = 17.445(5), b = 18.234(3), c = 9.033(3) Å; α = 92.74(2), β = 102.59(3), γ = 78.52(2)°; Z = 1.