Stepwise Host–Guest [2 + 2] Photoreaction in a Hydrogen-Bonded One-Dimensional Coordination Polymer to a Two-Dimensional Layered Structure

Abstract

Two hydrogen-bonded interdigitated one-dimensional (1D) coordination polymers (CPs) were synthesized from Cd­(II) nitrate and 1,4-benzenedicarboxylate (bdc) with two 4-styrylpyridine (4spy) derivatives. In the solid state structure of 1D CP containing 2′-fluorostyrylpyridine (2F-4spy), a guest 2F-4spy was sandwiched between the terminal 2F-4spy ligands and the CC bonds of all the 2F-4spy are well-aligned in <i>host–guest-host–host-guest–host</i>- sequence infinitely. From time-dependent photoreaction studies, it has been found that the [2 + 2] photocycloaddition occurs between <i>host–guest</i> molecules first followed by <i>host–host</i> pairs in a two-step process, which resulted in the quantitative conversion of CC bond pairs to cyclobutane rings. It is a rare quantitative photoreaction between the <i>host</i> and <i>guest</i> molecules. Further, solvothermal crystallization of the final photoproduct furnished an interesting three-dimensional CP with <b>bcg</b> topology. Interestingly, 2NO₂-4spy also furnished a similar hydrogen-bonded 1D CP with parallel orientation of olefin bonds. Although the olefin bonds satisfy the Schmidt’s criteria for photoreactivity, it was found to be photoinert under UV light. This has been attributed to the steric hindrance caused by NO₂ substituent or the electron withdrawing effect