Inorganic Chemistry, Vol.38, No.9, 2204-2210, 1999
Analysis of bonding and d-electron count in the transition-metal carbides and transition-metal-silicide carbides with discrete linear M-C-M units (M = Cr, Fe, Re) by electronic structure calculations
Electronic structures of the silicide carbides Tm2Fe2Si2C, Th2Re2Si2C, and ThFe2SiC and the carbide Ho2Cr2C3 were calculated, using the extended Huckel tight binding method, to probe the d-electron counts of their transition metal atoms M (Cr, Fe, Re) the bonding of their linear M-C-M (M = Cr, Fe, Re) units. The nature of the short interlayer X ... X (X = C, Si) bonds in Tm2Fe2Si2C, Th2Re2Si2C, and Ho2Cr2C3 was also examined. Our study shows that the M-C bonds of the M-C-M units exist as double bonds. There is significant bonding in the interlayer Si Si contacts of the silicide carbides R2M2Si2C (M = Fe, Re). The transition-metal atoms exist as d(10) ions in Tm2Fe2Si2C and Th2Re2Si2C. The d-electron count is slightly lower than d(10) in ThFe2SiC and close to d(5) in Ho2Cr2C3.