Combined photoelectron-photoabsorption study of (η-cycloheptatrienyl)(η-cyclopentadienyl)tungsten

Abstract

Gas-phase UV photoelectron spectra of the mixed sandwich complexes W(η-C 7H 7)(η-C 5SHS) and W(η-C 7H 7)(η-C 5H 4Me) and photoabsorption spectra of W(η-C 7H 7)(η-C 5H 5) have been measured. The first ionization band of the photoelectron (PE) spectra, assigned to the 2A 1 ion state is very sharp, indicating a non-bonding orbital. The second band assigned to the 2E 2 ion state shows a splitting of 0.35 eV, the low ionization energy component being 1.5 times the intensity of the higher component. The splitting is primarily due to spin-orbit coupling, but the unequal intensities indicate that the Ham effect is operative with Jahn-Teller distortion of the C 7H 7 ring competing to lift the degeneracy of the 2E 2 ion state. The gas-phase electronic absorption spectrum shows comparatively sharp Rydberg bands which disappear in the solution spectrum. All Rydberg excitations originate from the non-bonding metal 5d(a 1, σ +) orbital. A complete interpretation of the Rydberg structure has been given. In the short-wavelength pattern of the spectrum there are three Rydberg series with quantum defects of 3.26, 3.04 and 2.82 arising from the R np(π), R np( σ +) and R nd(π) transitions respectively. The convergence limit of these series lies at 5.53 eV, being in good agreement with the value for first ionization potential of W(η-C 7H 7)(η-C 5H 5) determined by PE spectroscopy. Below 37 000 cm −1, the spectrum reveals several peaks which were assigned on the basis of their term values to the R6s( σ +) R6p(π), R6p( σ +), R6d(π) and R7p(π) transitions. The R6p(π) state shows unusual splitting arising from the spin-orbit coupling induced by an admixture of the valence-shell excited states derived from d-d transitions. The vibronic structures of low-lying Rydberg bands has been analysed.