Two Zn(II) coordination polymers constructed from sulfate and isomeric viologen-carboxylate ligands: Crystal structures, photochromism and ammonia vapochromism

Nowadays, the exploration of chromic materials has been highly desirable owing to their appealing applications. In this work, two Zn(II) coordination polymers constructed from sulfate and isomeric viologen-carboxylate ligands, formulated as {[Zn(L1) (SO4)](H2O)2}n (1), {[Zn(L2) (SO4) (H2O)2](H2O)3}n (2) (L1 = N-(3-carboxy(pyridin-2-yl))-4,4′-bipyridinium, L2 = N-(4-carboxypyridin-3-yl)-4,4′-bipyridinium) have been synthesized and characterized. Single crystal X-ray analyses reveal that 1 features a 2D layer structure and 2 discloses a 1D chain structure. As expected, 1 and 2 exhibit sensitive photochromic properties under xenon light irradiation due to the formation of photoinduced radicals. Moreover, 1 displays a color change detectable by the eye when exposed to ammonia vapor. These results provide some useful guidance to explore new chromic crystalline materials.