Electronic structure and conformational isomerism of the digermene (tBu2MeSi)2Ge=Ge(SiMetBu2)2 as studied by temperature-dependent Raman and UV–vis spectra and quantum-chemistry calculations

Abstract

The structure of the digermene (tBu2MeSi)2Ge=Ge(SiMetBu2)2 (1) was investigated by experimental (Raman and UV–vis) as well as computational (NCA, TD DFT and QTAIM) methods. Temperature-dependent Raman and UV–vis spectra have demonstrated that 1 does not dissociate into the corresponding germylenes on heating either to 120 °C as a solid or to 80 °C in solution, thus preserving the integrity of its double Ge=Ge bond. Raman and NCA results allowed one to estimate the region of the νGe=Ge vibrational frequency in the spectra of digermenes as 270–340 cm−1. When illuminated with a red laser beam of enhanced power (>5 mW), solid 1 undergoes a transformation followed by disappearance of the νGe=Ge Raman band. This process is evidently photodissociation caused by proximity of the red laser wavelength 632.8 nm to the intrinsic absorption of 1 at 616 nm. Temperature dependence of the Raman spectrum has revealed conformational isomerism in solid digermene 1 due to hindered rotation about the Ge–Si bonds, the conformers differing in mutual disposition of Me and bulky tBu groups.