Solvent and additive-controlled supramolecular isomerism in zinc coordination polymers

A new series of Zn(II) supramolecular isomers containing ditopic 1,3-di(pyridin-4-yl)urea (4bpu) ligand were synthesized and characterized by infrared analysis, elemental analysis and TGA as well as single-crystal X-ray diffraction analysis. Four solvent-induced pseudopolymorphic zinc (II) coordination polymers (CPs), namely, {[Zn(4bpu)(OAc)₂](CH₃OH)}_n (1), {[Zn(4bpu)(OAc)₂](C₂H₅OH)}_n (2), {[Zn(4bpu)(OAc)₂](HOCH₂CH₂OH)}_n (3), and {[Zn(4bpu)(OAc)₂](0.5H₂O)}_n (4), were prepared by the reaction of Zn(OAc)₂.2H₂O and 4bpu via self-assembly under varying solvent systems. Also, a pair of polymorphic coordination polymers namely, {[Zn(4bpu)(OAc)₂](CH₃OH)}_n (1α) and {[Zn₃(4bpu)₃(OAc)₆](CH₃OH)₂}_n(1β), was prepared in the presence of different organic additives. Single-crystal X-ray diffraction confirmed that 1-4 and 1α display 1D polymeric zig-zag chains and 1β exhibits 1D triple-stranded ladders that were self-assembled through various supramolecular interactions. In addition, a series of dissolution-recrystallization structural transformations (DRST) were performed on these supramolecular isomers.