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 Tm(2)Fe(2)Si(2)C, Th(2)Re(2)Si(2)C, and ThFe(2)SiC and the carbide Ho(2)Cr(2)C(3) were calculated, using the extended Hückel 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 Tm(2)Fe(2)Si(2)C, Th(2)Re(2)Si(2)C, and Ho(2)Cr(2)C(3) 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 R(2)M(2)Si(2)C (M = Fe, Re). The transition-metal atoms exist as d(10) ions in Tm(2)Fe(2)Si(2)C and Th(2)Re(2)Si(2)C. The d-electron count is slightly lower than d(10) in ThFe(2)SiC and close to d(5) in Ho(2)Cr(2)C(3).
Koo
H.-J.
HJ
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204.
Whangbo
M.-H.
MH