Exploring the structural landscape of 2-(thiophen-2-yl)-1,3-benzothiazole: high-Z′ packing polymorphism and cocrystallization with calix[4]tube

Abstract

We report here for the first time a cocrystal of the so-called neutral calix[4]tube, which is two tail-to-tail-arranged and partially deprotonated tetrakis(carboxymethoxy)calix[4]arenes, including three sodium ions, with 2-(thiophen-2-yl)-1,3-benzothiazole, namely trisodium bis(carboxymethoxy)bis(carboxylatomethoxy)calix[4]arene tris(carboxymethoxy)(carboxylatomethoxy)calix[4]arene–2-(thiophen-2-yl)-1,3-benzothiazole–dimethyl sulfoxide–water (1/1/2/2), 3Na+·C36H30O12 2−·C36H31O12 −·C11H7NS2·2C2H6OS·2H2O, which provides a new approach into the host–guest chemistry of inclusion complexes. Three packing polymorphs of the same benzothiazole with high Z′ (one with Z′ = 8 and two with Z′ = 4) were also discovered in the course of our desired cocrystallization. The inspection of these polymorphs and a previously known polymorph with Z′ = 2 revealed that Z′ increases as the strength of intermolecular contacts decreases. Also, these results expand the frontier of invoking calixarenes as a host for nonsolvent small molecules, besides providing knowledge on the rare formation of high-Z′ packing polymorphs of simple molecules, such as the target benzothiazole.