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

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 >> (RCOOHHOOCR)-H-... > RB(OH)(2)(HOOCR)-H-... > RB(OH)(2)(...)(HO)(2)BR; (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 (RCOOHHOOCR)-H-... and RB(OH)(2)(...)(HO)(2)BR 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)-H-... heterodimers are intermediate between the energies for the corresponding (RCOOHHOOCR)-H-... and RB(OH)(2)(...)(HO)(2)BR 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.