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

Abstract

The measured Raman and IR spectra of solid, polycrystalline bis(pentamethylcyclopentadienyl)dizinc, (η⁵-C₅Me₅)₂Zn₂, <b>1</b>, and bis(pentamethylcyclopentadienyl)monozinc, (η⁵-C₅Me₅)(η¹-C₅Me₅)Zn, <b>8</b>, are reported in some detail. The IR spectra of the vapors of <b>1</b> and <b>8</b> 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 <b>1</b> and <b>8</b> 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 <b>1</b> 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 <b>1</b>.