Two cases of bipyridinium-based metal-organic frameworks: Syntheses, structures, photochromic behaviors

Two novel bipyridinium-based metal-organic frameworks Zn[(pbpy)(0.5)(m-BDC)Cl]center dot 1.5H(2)O(1) and Cd [(PbPY)(0.5)(m-BDC)Cl]center dot H2O(2)center dot(PbPycl(2) = 1,1'-[1,4 phenylenebis-(methylene)This(4,4' bipyridinium) - dichloride) have been synthesized and structurally characterized by single crystal X-ray crystallography. Both of them show 2D layered window structures. When they are irradiated by 300 W Xenon lamp, both of them exhibit photochromic behaviors which are attributed to the process of intermolecular electron transfer to generate pbpycl(2) free radicals. These processes have been demonstrated by UV-Vis absorption characterization analysis, electron spin resonance (ESR). The photoproduct of compound 1 is more stable than compound 2 in air. Photochromic mechanisms and the relationships between structures and properties have been discussed adequately.