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 R
2
2(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.
A one‐pot double condensation reaction between 3‐aminophenylboronic acid monohydrate and 2,6‐pyridincarboxyaldehyde forms the very interesting building block bisboronic dicationic acid (1), the reaction was carried out in methanol with the presence of sulfuric acid as catalyst. The product contains a central core consisting of five delocalized fused heterocycles being a dicationic moiety and including methylsulfate (CH3OSO3−) as anion (1a). Treatment with CaCl2 under heating produces the anion interchange leading the chloride as anion (1b). Both salts were crystallized by slow solvent evaporation and the X‐ray diffraction analysis reveals the presence of O−H⋅⋅⋅O hydrogen bonds favoring the 2D supramolecular arrangements. Three different motives were formed for 1a with the participation of water molecules, the methylsulfate anion and the boronic acid groups; by the way for 1b, the chloride anion interacts with a BOH group as well as a methanol molecule trough hydrogen bonds, additionally an electrostatic interactions were found with the cationic five membered rings. The possibility for syn‐anti isomerization at room temperature is confirmed by computations with a weak energy barrier of 17.7 kcal mol−1.
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