Crystal engineering with isosteric triether and triamine linked aromatic tri-carboxylic acids: iso-structurality and synthon interplay in their co-crystals and salts with bis(pyridyl) derivatives

Abstract

Conformationally flexible triacids H₃tcpb and H₃btab having ether and amine linkages, respectively, have been studied to examine the molecular and supramolecular similarities in their crystal structures and also in those of cocrystals and salts with bispyridyl molecules. Both the acids exhibited unsymmetrical but almost identical geometries in all the crystal structures studied here. In their crystal structures these molecules were found to exhibit one-dimensional isostructurality via acid–acid homo synthons. 1D-chains of H₃tcpb and H₃btab molecules assembled further via C–H⋯O and N–H⋯O hydrogen bonds, respectively, to form 2D-layers. The acid H₃tcpb showed a lesser tendency to form single crystals of complexes (three) with bispyridyl molecules compared to H₃btab (five). In all the complexes, acid–pyridine heterosynthons were found to play an important role in assembling the molecules. However, the homosynthon-I was observed in four out of eight complexes studied here and all from amine linked triacids (H₃btab). Furthermore, the complexes of H₃tcpb exhibited red shifted luminescence, whereas those of H₃btab exhibited a blue shift (λ_ex. = 330 nm) with respect to parent acids.