名称:
Methylidyne XC⋮MX3 (M = Cr, Mo, W; X = H, F, Cl) Diagnostic C−H and C−X Stretching Absorptions and Methylidene CH2MX2 Analogues
摘要:
Laser-ablated Cr, Mo, and W atoms react with di-, tri-, and tetrahalomethanes to form XC=MX3 (M Mo, W; X = H, F, Cl) methylidyne molecules as major products. Dihalomethanes also give a minor yield of CH2=MX2 methylidenes. The electronic state and bonding changes in the CH2=CrCl2, CH2=CrFCl, and CH2-CrF2 methylidene series, but the Mo and W counterparts are calculated to be triplet state CH2=MX2 molecules. Identifications of these new carbon-metal multiple bond species are made through isotopic substitution (D, C-13) and isotopic frequency calculations using density functional theory. The HC=MX3 molecules exhibit C-H stretching frequencies in the 3030-3090 cm(-1) region and C=M stretching frequencies in the 1007-980 cm(-1) range, which vary slightly with the carbon hybridization as determined by the substituents employed here. The XC=MX3 molecules show very high C-X stretching frequencies in the 1540-1520 cm(-1) region for X = F and 1300-1230 cm(-1) for X = Cl due to strong bonds and the antisymmetric nature of the X-C-M vibrational mode.