Exploring the effect of substitution patterns on the symmetry of hydrogen-bonded supramolecular motifs in functionalized benzosiloxaboroles

Abstract

Crystal structures of a series of 26 functionalized 3-hydroxybenzo[c][1,2,3]siloxaboroles were compared taking into account electronic and steric effects of substituents at the aromatic ring on the hydrogen-bond (HB) motifs involving B–OH groups. The supramolecular assemblies of those compounds show strong variation depending on the number, position and type of substituents. Thus, HB dimers, trimers, tetramers and chains are formed. Most 7-substituted derivatives are isomorphous and crystallize in the I4₁/a tetragonal space group of symmetry featuring cyclic propeller-like tetramers as a characteristic structural motif. DFT calculations revealed that all observed HB motifs are characterized by similar stabilization energies ranging from −25 to −35 kJ mol⁻¹ per molecule, which rationalizes the strong diversification of HB motifs in the studied structures.