Theoretical and Experimental Evaluation of Homo- and Heterodimeric Hydrogen-Bonded Motifs Containing Boronic Acids, Carboxylic Acids, and Carboxylate Anions: Application for the Generation of Highly Stable Hydrogen-Bonded Supramolecular Systems

Abstract

The hydrogen-bonding interaction energies have been computed for a series of five homo- and heterodimers formed between boronic acids, carboxylic acids, and carboxylate anions using ab initio methods at the MP2/6-31G(d,p) level. The results show that the stability of these systems decreases in the following direction: RB(OH)2···-OOCR > RCOOH···-OOCR >> RCOOH···HOOCR > RB(OH)2···HOOCR > RB(OH)2···(HO)2BR; (R = Me, Ph). Five crystals containing boronic acids and carboxylate anions have been prepared and characterized both in solution and the solid-state using spectroscopic as well as X-ray crystallographic methods. The interaction energies of the RB(OH)2···-OOCR heterodimeric motifs are more than double those of the homodimeric RCOOH···HOOCR and RB(OH)2···(HO)2BR motifs. This was proved by the fact that these anionic systems were stable in solution, even in polar solvents such as DMSO. The solid-state analysis provided detailed geometric data for one of these systems. The predicted interaction energies for the RB(OH)2···HOOCR heterodimers are intermediate between the energies for the corresponding RCOOH···HOOCR and RB(OH)2···(HO)2BR homodimers; nevertheless, crystals containing such a system could not be obtained. Despite of this, these experiments provided two new systems containing hydrogen-bonding interactions between neutral carboxylic and boronic acids.