Experimental and theoretical studies of molecular complexes of theophylline with some phenylboronic acids

Abstract

Molecular complexes of the active pharmaceutical ingredient (API) theophylline, 1 with 4-halophenylboronic acids [4-chlorophenylboronic acid (a), 4-bromophenylboronic acid (b), 4-iodophenylboronic acid (c)], 4-hydroxyphenylboronic acid (d) and 1,4-phenylene-bis-boronic acid (e) have been reported. The complexes were characterized and analysed using the intensity data obtained by X-ray diffraction techniques. All the halo substituted boronic acid complexes are found to be isostructural (1.a, 1.b and 1.c) irrespective of the variations in size and electronegativity of halogen atoms while complexes with non-halogenated boronic acids, 1.d and 1.e, show distinctly different features between themselves as well as with that of 1.a–c, both in two and three-dimensional arrangements. Complexes 1.a–c are noted to be crystallized in the form of sheet structures, which are stacked in three dimensional arrangements, while channels and square grid networks are observed in 1.d and 1.e, respectively. Further the homomeric and heteromeric interactions which occur in the complexes have been analysed by a DFT-D3 method.