Vibrational spectra of nitrosyl-substituted transition-metal hydride complexes: an experimental and theoretical study of carbonyldihydronitrosyl(trimethylphosphine)rhenium ([Re(CO)H₂(NO)(PMe₃)₂])

The vibrational frequencies of carbonyldihydronitrosyl(trimethylphosphine)rhenium ([Re(CO)H₂(NO)(PMe₃)₂]; 1 a) and of its deuterated derivatives 1 b and 1 c have been investigated by IR and Raman spectroscopy (only 1 a) and by gradient-corrected density-functional calculations. Complex 1 a possesses two well separatedn vReH stretching vibrational modes, which couple with the vXO stretching mode (X=N, C) of the ligand in trans position, but which do not couple with each other. These modes significantly differ in their IR intensities, so that only the vReH band of the H-ligand trans to the nitrosyl ligand can be observed in the experiment. With Raman spectroscopy, both vReH stretching vibrational modes can be observed. Computed frequencies, IR intensities, and force constants are presented. The influence of basis-set size and of the accuracy of the numerical integration scheme is investigated: the correct description of the intensities requires large basis sets and accurate numerical integration. Calculations have been extended to include the complexes [Re(CO)H₂(NO)(PH₃)₂] (2) and [Re(CO)H₂(NO)(PF₃)₂] (3) in order to study influences of different P-donor ligands.