Measurements of the microwave spectrum, Re–H bond length, and Re quadrupole coupling for HRe(CO)5

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Abstract
Rotational transition frequencies for rhenium pentacarbonyl hydride were measured in the 4–10 GHz range using a Flygare–Balle type microwave spectrometer. The rotational constants and Re nuclear quadrupole coupling constants for the four isotopomers, (1) H187Re(CO)5, (2) H185Re(CO)5, (3) D187Re(CO)5, and (4) D185Re(CO)5, were obtained from the spectra. For the most common isotopomer, B(1)=818.5464(2) MHz and eq Q(187Re)=−900.13(3) MHz. The Re–H bond length (r 0) determined by fitting the rotational constants is 1.80(1) Å. Although the Re atom is located at a site of near‐octahedral symmetry, the quadrupole coupling is large due to the large Re nuclear moments. A 2.7% increase in Re quadrupole coupling was observed for D‐substituted isotopomers, giving a rather large isotope effect on the quadrupole coupling. The Cax–Re−Ceq angle is 96(1)°, when all Re–C–O angles are constrained to 180°.