Dihydrogen Bonds in Salts of Boron Cluster Anions [BnHn]2- with Protonated Heterocyclic Organic Bases

Dihydrogen bonds attract much attention as unconventional hydrogen bonds between strong donors of H-bonding and polyhedral (car) borane cages with delocalized charge density. Salts of closo-borate anions [B10H10](2-) and [B12H12](2-) with protonated organic ligands 2,2'-dipyridylamine (BPA), 1,10-phenanthroline (Phen), and rhodamine 6G (Rh6G) were selectively synthesized to investigate N-H center dot center dot center dot H-B intermolecular bonding. It was found that the salts contain monoprotonated and /or diprotonated N-containing cations at di ff erent ratios. Protonation of the ligands can be implemented in an acidic medium or in water because of hydrolysis of metal cations resulting in the release of H3O+ cations into the reaction solution. Six novel compounds were characterized by X-ray di ff raction and FT-IR spectroscopy. It was found that strong dihydrogen bonds manifest themselves in FT-IR spectra that allows one to use this technique even in the absence of crystallographic data.