IR and Raman Characterization of the Zincocenes (η5-C5Me5)2Zn2 and (η5-C5Me5)(η1-C5Me5)Zn

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Abstract
The measured Raman and IR spectra of solid, polycrystalline bis(pentamethylcyclopentadienyl)dizinc, (η5-C5Me5)2Zn2, 1, and bis(pentamethylcyclopentadienyl)monozinc, (η5-C5Me5)(η1-C5Me5)Zn, 8, are reported in some detail. The IR spectra of the vapors of 1 and 8 each trapped in a solid Ar matrix at 12 K confirm the essentially molecular character of the solids. The experimental results have been interpreted with particular reference (i) to the corresponding spectra of 68Zn-enriched samples of the compounds, and (ii) to the spectra simulated by density functional theory (DFT) calculations at the B3LYP level. The marked differences of structure of 1 and 8 contrast with the relatively close similarity of their vibrational spectra, disparities being revealed only on detailed scrutiny, including the effects of 68Zn enrichment, and primarily at wavenumbers below 1000 cm−1. The Zn−Zn stretching motion of 1 features not as a single, well-defined mode identifiable with intense Raman scattering but in several normal modes which respond in varying degrees to 68Zn substitution. A stretching force constant of 1.42 mdyne Å−1 has been estimated for the Zn−Zn bond of 1.