Vibrational spectra of nitrosyl-substituted transition-metal hydride complexes: An experimental and theoretical study of carbonyldihydronitrosyl(trimethylphosphine) rhenium ([Re(CO)H-2(NO)(PMe3)(2)])

The vibrational frequencies of carbonyldihydronitrosyl(trimethylphosphine)r henium ([Re(CO)H-2(NO)(PMe3)(2)]; 1a) and of its deuterated derivatives 1b and 1c have bern investigated by IR and Raman spectroscopy (only 1a) and by gradient-corrected density-functional calculations. Complex 1a possesses t wo well separated <(nu)over tilde>(ReH) stretching vibrational modes, which couple with the <(nu)over tilde>(XO) stretching mode (X = N, C) of the lig and in trans position, but which do not couple with each other. These modes significantly differ in their IR intensities, so that only the <(nu)over t ilde>(ReH) band of the H-ligand trans to the nitrosyl ligand can be observe d in the experiment. With Raman spectroscopy, both <(nu)over tilde>(ReH) st retching vibrational modes can be observed. Computed frequencies, IR intens ities, and force constants are presented. The influence of basis-set size a nd of the accuracy of the numerical integration scheme is investigated: the correct description of the intensities requires large basis sets and accur ate numerical integration. Calculations have been extended to include the c omplexes [Re(CO)H-2(NO)(PH3)(2)] (2) and [Re(CO)H-2(NO)(PF3)(2)] (3) in ord er to study influences of different P-donor ligands.