Polycarbodiimidogermylene: synthesis, characterization, properties and theoretical studies

Polycarbodiimidogermylene was prepared by transmetallation between dichlorogermylene, dioxane (I) and dilithium cyanamide, by transamination between bis(triethylgermyl)carbodiimide and (I), or by dehydrochloration between (I) and carbodiimide in the presence of triethylamine. The germylene structure was confirmed by its reactivity with 3,5-di-t-butylorthocatechol, which preserves the germylene structure, and with 3,5-di-t-butylorthoquinone, which leads to the expected spirogermane. The carbodiimide form was evident by its infrared spectrum, in agreement with DFT/B3LYP calculations. Geometry optimizations of isomers of the carbodiimide and cyanamide forms for ClGe(NCNGe)nCl (n=1–3) confirm that the carbodiimide form is thermodynamically more stable by at least 10 kcal mol−1. By the reaction of polycarbodiimidogermylene with dimethyldisulfide the number of terminal chlorine atoms in the polymer chains was found to be between 12 and 14 NCN groups per 2 chorines, as was further confirmed by elemental analyses. Polycarbodiimidogermylene is a semiconductor, having a volume conductivity of about 10−2 S cm−1. Its UV spectrum shows absorptions between 650 and 2000 nm corresponding to transitions between 0.6 and 1.9 eV, confirming transitions in the forbidden gap.