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

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 (r₀) 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 C_ax-Re-C_eq angle is 96(1)°, when all Re-C-O angles are constrained to 180°.