Structural diversity and luminescence of zinc coordination polymers constructed by flexible ligands

Abstract

Three new zinc coordination polymers based on the flexible ligand L (5,5′-((1,3-phenylenebis(methylene))bis(oxy))diisophthalic acid) have been prepared by solvothermal synthesis, which was named for [Zn4(L)2(pdp)(H2O)5]n (1), {[Zn(L)0.5(pdp)]·(NMP)0.5}n (2) and {[Zn(L)0.5(bpp)]·3H2O}n (3) (pdp=trans-1,2-bis(4-pyridyl)ethylene), bpp = 4,4′-(1,3-propanediyl)bis-pyridine) respectively. By controlling the length of auxiliary ligands, compounds 1 and 3 can be assembled under similar reaction conditions with different 3D structures. Although the ligands are all achiral components, it is interesting to note that compound 1 crystallizes in P21 chiral space group. The two Zn ions are in an asymmetric coordination environment resulting in symmetric breaking, which might be the reason compound 1 crystallizes in the chiral space group. While, compound 3 is composed of two identical 2D layers interpenetrating with each other, displaying a 2D + 2D → 3D polycatenation network. By changing the solvent and temperature, compound 2 can be available which presents a 3D structure with a two-fold interpenetrating framework, and the guest accessible volume (2414 Å3 per unit cell) accounts for 16.8% of the unit cell volume. In addition, compounds 1–3 have also had their solid-state luminescence characteristics, powder X-ray diffraction, and thermal stabilities examined.