| Abstrakt: |
Photofragment spectroscopy is used to measure the vibrational spectra of M+(CH4)(Ar) and M+(CH4)n(M = Ti, V; n= 1–4) in the C–H stretching region (2550–3100 cm–1). Spectra were measured by monitoring the loss of Ar from M+(CH4)(Ar) and loss of CH4from 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–1due 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–1due to the C–H stretch of hydrogens pointing away from the metal. The symmetric proximate C–H stretches of M+(CH4)(Ar) to M+(CH4)4are red-shifted from the symmetric stretch in bare CH4by 149, 152, 128, and 107 cm–1for the titanium complexes and 164, 175, 158, and 146 cm–1, respectively, for the vanadium complexes. In M+(CH4)(Ar) (M = Ti, V), the heavy atoms are collinear. Ti+(CH4)(Ar) has η3methane hydrogen coordination (∠M–C–H = 180°), while V+(CH4)(Ar) has η2(∠M–C–H = 124°). The n= 2 complexes have C–M–C linear. Ti+(CH4)2has C2hsymmetry with η3CH4while V+(CH4)2has methane coordination intermediate between η2and η3(∠M–C–H = 156°). Both the M+(CH4)3(M = Ti, V) complexes have C2vsymmetry with one methane farther away from the metal in an η2binding orientation and two methanes close to the metal with a nearly η2methane for vanadium and coordination between η2and η3CH4for titanium (∠M–C–H = 150°). In Ti+(CH4)4and V+(CH4)4all of the methanes have η2coordination. The titanium complex has a distorted square planar geometry with two different Ti–C bond lengths and the vanadium complex is square planar. |
