Abstract
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...H−B intermolecular bonding. It was found that the salts contain monoprotonated and/or diprotonated N-containing cations at different 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 diffraction 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.
Highlights
The term “secondary bonds” was introduced by Alcock almost 50 years ago [1] when he described weak bonds found in crystals of inorganic compounds which are shorter than the sum of the wan derWaals radii of the atoms involved in the interaction but longer than the covalent bonds
We focused on so-called dihydrogen bonds (DHB) that arise between B–H groups of boron clusters and a protic hydrogen moiety (H–X)
The target salts of the boron cluster anions and N-containing cations were synthesized by the reaction between salts [Et3 NH]2 [B10 H10 ] or [Et3 NH]2 [B12 H12 ] and neutral organic bases Phen, BPA in the presence of CF3 COOH in CH3 CN and CH3 CN/water
Summary
Waals radii of the atoms involved in the interaction but longer than the covalent bonds. These bonds are called non-bonding or non-valent specific bonds [2,3,4,5]. Among all types of non-bonding bonds, hydrogen bonds were the only ones to be considered in detail for a long time, as this type of bond is the most important among intermolecular interactions [6,7,8]. There is no doubt that these interactions play a critical role in the organization of the structure of solid compounds and packing, which directly affects their properties. A great number of studies are devoted to this problem, and this topic remains of current interest
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