Vibrational spectra hydride complexes

Under syn gas pressure the rhodium acac precursors were converted to the catalytically active hydride complexes HRh(CO)2(L-L). The complexes are generally assmned to have a trigonal bipyramidal structure and two isomeric structures of these complexes are possible, containing the diphosphite coordinated in a bisequatorial (ee) or an equatorial-apical (ea) fashion. The structure of the complexes can be elucidated by (high pressure) IR and NMR data (Table 3). In the carbonyl region of the infrared spectrum the vibrations of the ee and ea complex can be easily distinguished. The ee complexes typically show absorptions around 20 15 and 2075 cm [24, 26,... 

HaU and coworkers used density functional theory calculations to assign the inelastic neutron scattering derived vibrational spectrum of the elongated dihydrogen complex, (Tp )Rh(H)2(/ -H2) [66], They conclude that the H-H distance derived from neutron diffraction for the (Tp )Rh(H)2( / -H2) complex may in fact correspond to the average of the H-H distances of the tetrahydride and bis-hydride/// -H2 species. 

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