MICROWAVE MEASUREMENTS AND CALCULATIONS ON THE MOLECULAR-STRUCTURE OFTETRACARBONYLDIHYDRORUTHENIUM

The microwave rotational spectra for seven isotopomers of tetracarbony ldihydroruthenium were measured in the 4-12 GHz range using: a Flygare -Balle type microwave spectrometer. The measured transition frequencie s could be fit to within a few kilohertz using a rigid rotor Hamiltoni an with centrifugal distortion. The rotational constants for the most abundant isotopomer are A = 1234.2762(4), B = 932.7016(6), and C = 811 .6849(6) MHz. The dipole moment is aligned with the c axis of the comp lex. The 21 measured rotational constants were used to determine the f ollowing structural parameters: r(Ru-H)=1.710(23) Angstrom, r(Ru-C1)=1 .952(21) Angstrom, r(Ru-C3)=1.974(28) Angstrom, angle(H-Ru-H)= 87.4(2. 4)degrees, angle(C1-Ru-C2)= 160.6(4.3)degrees, angle(C3-Ru-C4)=101.4(1 .5)degrees, and angle(Ru-C1-O1)=172.6(7.6)degrees. The axial carbonyl groups are bent slightly toward the hydrogen atoms. These structural p arameters are in excellent agreement with the substitution coordinates determined from the Kraitchman equations, and with the structural par ameters calculated using density functional theory. There was no previ ous structural data on this complex. The results of the microwave data and theoretical calculations both indicate C-2v molecular symmetry, a nd show that the H atoms are separated by about 2.36 Angstrom. These r esults indicate that this complex is clearly a ''classical dihydride'' rather than an eta(2)-bonded, ''dihydrogen'' complex. Fairly large de uterium isotope effects were observed for the Ru-H bond length and H-R u-H angle. The r(0), Ru-D bond lengths were observed to be 0.03(2) Ang strom shorter than the ro, Ru-H bond lengths. The D-Ru-D angle is 1.1 degrees less than the H-Ru-H angle indicating that the anharmonicity e ffects are comparable for the bond lengths and for the interbond angle . The new results on this complex are compared with previous results o n the Similar dihydride complexes, H2Fe(CO)(4), and H2Os(CO)(4). (C) 1 998 American Institute of Physics. [S0021-9606(98)01443-3].