Vibrational spectra and electronic structure of germatranols (HO)4 − n Ge(OCH2CH2)nNR3 − n (R = H; n = 1–3) with transannular Ge⋯N bonding

Series of germatrane compounds with OH functionality and Ge⋯N transannular bonding, i.e. 1-germatranol (I), 1,1-quasigermatranol (II) and 1,1,1-hypogermatranol (III) with general formula (HO)4 − nGe(OCH2CH2)nNR3 − n (R = H, Me; n = 1–3) are synthetized and their solid state IR spectra are recorded. Equilibrium structures and vibrational spectra of monomeric and centrosymmetric dimeric species of these compounds are predicted by the DFT B3LYP/aug-cc-pVDZ method. The assignment of the vibrational spectra of I–III was carried out based on theoretical IR spectra scaled with factors obtained earlier for halogermatranes to take account of the substantial and systematic discrepancy between Ge⋯N interatomic distance of the gas phase and theoretical predictions on the one hand and X-ray solid state data on the other. Dimeric models provide a good agreement between experimental and predicted frequencies, including GeOH bending modes, of I, crystalline state of which is formed by dimers, and slightly worse for II, in which some weaker O–H⋯O and N–H⋯O hydrogen bonds are not considered in the dimeric model. However, this model for III is poor since it does not take into account hydrogen bonding of “free” OH and NH2 groups. Despite the steady decrease of the Ge⋯N interatomic distance, corresponding frequencies demonstrate the substantial increase on going from I to II and practically no increase from II to III.