Boron-π interactions in two 3-(dihydroxyboryl)anilinium salts analyzed by crystallographic studies and supported by the noncovalent interactions (NCI) index theoretical approach

Abstract

In the title compounds, 3-(dihydroxyboryl)anilinium bisulfate monohydrate, C₆H₉BNO₂⁺·HSO₄^-·H₂O (I), and 3-(dihydroxyboryl)anilinium methyl sulfate, C₆H₉BNO₂⁺·CH₃SO₄^- (II), the almost planar boronic acid molecules are linked by pairs of O-H...O hydrogen bonds, forming centrosymmetric motifs that can be described by the graph-set R₂²(8) motif. In both crystals, the B(OH)₂ group acquires a syn-anti conformation (with respect to the H atoms). The presence of the hydrogen-bonding functional groups B(OH)₂, NH₃⁺, HSO₄^-, CH₃SO₄^- and H₂O generates three-dimensional hydrogen-bonded networks, in which the bisulfate (HSO₄^-) and methyl sulfate (CH₃SO₄^-) counter-ions act as the central building blocks within the crystal structures. Furthermore, in both structures, the packing is stabilized by weak boron-π interactions, as shown by noncovalent interactions (NCI) index calculations.

Keywords: anilinium; bisulfate; boron–π interactions; crystal structure; dihydroxyboryl; hydrogen bonds; organoboronic acid; supramolecular synthons.