Measurements of the microwave spectrum and calculations of the molecular structure for η4-butadiene osmium tricarbonyl

Abstract

The microwave spectrum of η⁴-butadiene osmium tricarbonyl was measured in the 6–12 GHz frequency range using a Flygare-Balle type pulsed beam Fourier transform microwave (FTMW) spectrometer. The rotational constants for the ¹⁹²Os isotopologues were determined to have the following values: A = 939.4(2), B = 849.08(1) and C = 816.71(1) MHz. The centrifugal distortion constant is D_J = 0.60(7) kHz. 16 a-dipole transitions were measured and included in the fit. Extensive high-level G16 calculations were made using DFT methods with various basis sets, including core-potentials (ECP). The best structure was calculated with Gaussian 16 using B3LYP/def2-QZVPP, which includes a core potential (ECP). The best calculated values are in very good agreement with the experimental values.