BONDING ANALYSIS IN INORGANIC TRANSITION-METAL CUBIC CLUSTERS - 3 - METAL-CENTERED TETRACAPPED M-9(MU(5)-E)(4)L-N SPECIES WITH A TETRAGONALDISTORTION

A number of main group element (E)-transition metal (M) cluster compun ds based upon a hexacapped M-8 cube have been reported in two configur ations: empty and with interstitial metal atoms in the center of the c ube. Related molecules arise upon slow oxidation of the reaction produ ct that forms when [Bi2CO4(CO)(11)](-) is treated with Mo(CO)(3)(tolue ne) giving Bi-Co clusters based upon tetragonally distorted tetracappe d cubic metal arrays with interstitial metal atoms. These compounds fo rmulated as [PPN](2)[Bi4Co9(CO)(16)]. 2THF ([PPN](2)[1]. 2THF) and [PP N](2)[Bi8Co14(CO)(20)]. 1.08THF([PPN](2)[2]. 1.08THF) have been charac terized via single-crystal X-ray diffraction. An alternative descripti on ascribes the metal cores to close-packed arrays based upon the cubo ctahedron. The complexes are electron rich via conventional electron-c ounting formalisms. To understand these molecules more fully, a thorou gh theoretical analysis of compounds [1](2-) and [2](2-) was undertake n. The calculations indicate that the bonding of the interstitial meta l atom with the metallic host somewhat differs from that found in thei r related metal-centered cubic species M-9(mu(4)-E)(6)L-8, due to stre tching along the 4-fold axis. The HOMO-LUMO region is slightly antibon ding between the Co-i atoms (i = interstitial) and the surrounding Bi and Co-p (p = peripheral) atoms. As with other members of this cubic c luster class, no HOMO-LUMO gaps are observed. The actual electron coun ts for [1]2(-) and [2](2-), however, favor stronger Co-p-Co-i and Bi-C o-i bonding than would be observed for the allowed higher electron cou nts. Crystallographic data for [PPN](2)[1]. 2THF: triclinic space grou p P (1) over bar; a = 13.560(5), b = 15.893(5), c = 11.884(4) Angstrom ; alpha = 105.26(2), beta = 98.25(3), gamma = 83.25(3)degrees; Z = 1. Crystallographic data for [PPN](2)[2]. 1.08THF: triclinic space group P (1) over bar; a = 17.445(5), b = 18.234(3), c =9.033(3) Angstrom; al pha = 92.74(2), beta = 102.59(3), gamma = 78.52(2)degrees; Z = 1.