Knowledge Bank

Microwave rotational spectra for six isotopomers of $H2Os(CO)4$ were measured in the 4-12 GHz range using a Flygare-Balle-type spectrometer. The 18 rotational constants from these isotopomers were used to determine eight structural parameters describing the gas-phase structure of this complex. This near-octahedral complex has $C2$, symmetry and the dipole moment lies along the c-principal axis for the normal isotopomer. The distance between H atoms, obtained directly from experimental structural parameters, is $rHH=2.40(2)$ \AA. This rather long H - H distance indicates that this is clearly a ""dihydride"" rather than a ""dihydrogen"" complex. The Os - H bond lengths are $rOsCl=1.72(1)$ \AA. The osmium-carbonyl carbon bond lengths for axial and equatorial carbonyl groups are $rosci=1.96(1)$ \AA and $roso3=1.97(2)$ \AA. Results for other structural parameters obtained using least squares fitting and the structural parameters obtained using the Kraitchman method are presented and discussed. No evidence for internal motion was observed for this complex.