Reactions of methane with hafnium atoms:: CH2=HfH2, agostic bonding, and (CH3)2HfH2

Laser-ablated hafnium atoms react with methane to form the methylidene complex CH2=HfH2. The activation of a second CH4 molecule forms (CH3)(2)HfH2 particularly on sample annealing. These molecules are identified from infrared spectra by isotopic substitution (CH4, (CH4)-C-13, CD4, CH2D2) and comparison to DFT frequency calculations. The computed structure for singlet ground state CH2=HfH2 shows CH2 and HfH2 distortion and evidence for agostic bonding (angle H-C-Hf, 95.6 degrees), which is more stable than the symmetrical nonagostic structure. The CHD=HfHD isotopic molecules provide experimental evidence for agostic bonding distortion. In addition, changes within the absorptions of the CHD=HfHD isotopic molecules on annealing the argon matrix to 20-26 K demonstrates facile interchange of the agostic bonding positions.