Structures of M(CH) (M = Ti, V) Based on Vibrational Spectroscopy and Density Functional Theory.

Photofragment spectroscopy is used to measure the vibrational spectra of M(CH)(Ar) and M(CH) (M = Ti, V; = 1-4) in the C-H stretching region (2550-3100 cm). Spectra were measured by monitoring the loss of Ar from M(CH)(Ar) and loss of CH from the larger clusters. The experimental spectra are then compared to simulations done at the B3LYP/6-311++G(3df,3pd) level of theory to identify the structures of the ions. The spectra all have a peak near 2800 cm due to the symmetric C-H stretch of the hydrogens adjacent to the metal. Some complexes also have a smaller peak due to the corresponding antisymmetric stretch. Most complexes also have a peak near 3000 cm due to the C-H stretch of hydrogens pointing away from the metal. The symmetric proximate C-H stretches of M(CH)(Ar) to M(CH) are red-shifted from the symmetric stretch in bare CH by 149, 152, 128, and 107 cm for the titanium complexes and 164, 175, 158, and 146 cm, respectively, for the vanadium complexes. In M(CH)(Ar) (M = Ti, V), the heavy atoms are collinear. Ti(CH)(Ar) has η methane hydrogen coordination (∠M-C-H = 180°), while V(CH)(Ar) has η (∠M-C-H = 124°). The = 2 complexes have C-M-C linear. Ti(CH) has symmetry with η CH while V(CH) has methane coordination intermediate between η and η (∠M-C-H = 156°). Both the M(CH) (M = Ti, V) complexes have symmetry with one methane farther away from the metal in an η binding orientation and two methanes close to the metal with a nearly η methane for vanadium and coordination between η and η CH for titanium (∠M-C-H = 150°). In Ti(CH) and V(CH) all of the methanes have η coordination. The titanium complex has a distorted square planar geometry with two different Ti-C bond lengths and the vanadium complex is square planar.