The rotational spectrum of the cyclopentadienylallylnickel complex

The rotational spectrum of cyclopentadienylallylnickel, C3H5NiC5H5, has been studied using a pulsed molecular beam Fourier transform microwave spectrometer. Twelve a-type transitions were analyzed to obtain rotational and centrifugal distortion constants for the parent C3H558NiC5H5 complex. The measured rotational constant A = 3107.603(93) MHz is about 160.0 MHz larger than the predicted DFT value, providing evidence for possible fluxional motion in the complex. The large distortion constants, on the order of 100 kHz, provide further evidence for fluxional motion. The experimental constants B = 1302.38(22) and C = 1276.40(15) MHz are in good agreement with the DFT calculated values and confirm the η3-bonding of the allyl ligand to the Ni-C5H5 moiety. DFT calculations provide a V5 barrier for internal rotation about the Ni-C5H5 axis of 53 cm−1, with the lowest energy conformation having the central allyl c-atom eclipsed with respect to two C5H5 carbon atoms. Several additional rotational lines, possibly those of an exited torsional state, were observed but not assigned.