Structure and Properties of 1,3-Phenylenediboronic Acid: Combined Experimental and Theoretical Investigations

Abstract

The structure and properties of 1,3-phenylenediboronic acid are reported. Molecular and crystal structures were determined by single crystal as well as by powder X-ray diffraction methods. Acidity constant, thermal behavior, and NMR characterization of the title compound were also investigated. In addition to the experimental data, calculations of rotational barrier and intermolecular interaction energies were performed. The compound reveals a two-step acid–base equilibrium with different pKa values. TGA and DSC measurements show a typical dehydration reaction with formation of boroxine. In crystals, hydrogen-bonded dimers with syn-anti conformation of hydroxyl groups form large numbers of ribbon motifs. The 2D potential energy surface scan of rotation of two boronic groups with respect to phenyl ring reveals that the rotation barrier is close to 37 kJ⋅mol−1, which is higher than the double value for the rotation of the boronic group in phenylboronic acid. This effect was ascribed to intermolecular interaction with C–H hydrogen atom located between boronic groups. Furthermore, the molecules in the crystal lattice adopt a less stable molecular conformation most likely resulting from intermolecular forces. These were further investigated by periodic DFT calculations supported by an estimation of dimer interaction energy, and also by topological analysis of electron density in the framework of AIM theory.

Analysis of solvent-accessible voids and proton-coupled electron transfer of 2,6-bis(1H-imidazol-2-yl)pyridine and its hydrochloride

“…Moreover, the stoichiometry of the reaction confirms two equivalents of HCl at the final point, reinforcing that protonation of both imidazole groups was taking place. This led us to suggest that two protonations were taking place with very close pK a values, thus making impos-sible the determination of their values by means of the first and second derivatives method (Adamczyk-Woźniak et al, 2019).…”

Covalent organic frameworks from a monomer with reduced symmetry: polymorphism and Sierpiński triangles

“…1). 40 This V-shaped ditopic linker can selfcondense into a 3-fold node with a boroxine ring through a dehydration reaction. Depending on the rotational configuration around the boroxine ring, two kinds of elementary nodes can form based on a homotactic or a heterotactic motif (Fig.…”

Hydrolytic Stability of Hydroxyphenyl Boronic Acids(HPBAs) and Employment of Poly(HPBAs) for Voltammetric Determination of Fluoride Levels in Dental Formulations and Beverages; Significance of Raw DPV Data for Chemometric Discrimination

“…They have provided spectrophotometric titration spectrums for 2,5-difluorinated and 2,3,6-trifluorinated PBAs, whose UV absorp-tion changes, in the region 230-280 nm, form the isosbestic point at 266 nm. Adamczyk-Wozniak et al [18] have published a paper about experimental and theoretical investigation on 1,3-phenylene-diBA acidity. Potentiometric and spectrophotometric titration curves, pKa determinations as well as the changes in the concentration of individual forms as a function of pH during potentiometric titrations are provided.…”

“…They have calculated its pKa value as 7.9, which was determined as 7.82 and 7.90 by spectrophotometric and potentiometric methods, respectively. Adamczyk-Wozniak et al [18] have determined pKa1 and pKa2 values for 1,3phenylene-diBA by both potentiometric and spectrophotometric titrations, while they have predicted same values with the Henderson-Hasselbalch equation implemented into the Origin Lab software. Corresponding pKa1 and pKa2 values were determined as 8.26 and 9.70 with potentiometric method and as 8.31 and 10.11 with spectrophotometric method.…”