Reactions of thorium atoms with polyhalomethanes:: Infrared spectra of the CH2=ThX2, HC÷ThX3, and XC÷ThX3 molecules

Laser-ablated thorium. atoms react with methylene fluoride to form singlet CH2=ThF2, with fluoroform to give triplet HC divided by ThF3, and with CF4 to produce triplet FC divided by ThF3 molecules as the major products trapped in solid argon. Infrared spectroscopy, isotopic substitution, and density functional theoretical calculations confirm the identity of these methylidene and methylidyne complexes. Parallels with the analogous chloromethane and Group 4 metal reaction products are discussed. Structure calculations show that the C=Th bond lengths decrease and the agostic distortion increases from CH2=ThF2 to CH2=ThFCl to CH2=ThCl2 for the methylidene complexes. The triplet-state HC divided by ThF3 and FC divided by ThF3 electron-deficient methylidyne complexes exhibit delocalized pi-bonding as evidenced by spin densities comparable to those calculated for the analogous zirconium complexes. Chlorine substitution for fluorine supports stronger C divided by Th bonds. Thus, thorium appears to react as the early transition-metal atoms with fluoro- and chloromethanes. However, there is a substantial contribution from Th 5f orbitals in addition to 6d in the SOMO forming the weak pi-bonds in these electron-deficient methylidyne complexes. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).