Organogermatranes and their cation radicals by EPR-spectroelectrochemistry and ab initio calculations

Abstract

The study of 1-R-substituted organogermatranes (R = aryl, substituted benzyl, heteroaryl, styryl, aryl ethynyl and OSiR3) by cyclic voltammetry and real-time EPR-spectroelectrochemistry supported by DFT B3LYP/LANL2DZ calculations showed that electron withdrawal from these compounds is electrochemically reversible and leads to cation radicals of different stability. For germatranes with HOMO mainly localized on the atrane cage N atom (3c-4e bonding), EPR spectroscopy and Fermi contact coupling from DFT B3LYP/LANL2DZ calculations revealed the absence of spin delocalization on Ge atom in the cation radicals. Initially in an endo-configuration in neural germatranes, N atom becomes planar in the corresponding cation radicals. When perturbed by ortho-halo substituents (o-X–C6H4; X = F, Br), Ge tends to hexa-coordinated geometry; for the cation radicals of other germatranes, flattening towards trigonal bipyramid is preferred. In these species, two types of transmission of electronic effects are realized (atrane-localization of spin upon aryl substitution and “spin-leakage” upon benzyl-like substitution) that makes these compounds promising for developing long-range conjugated systems for molecular electronics.