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

Two hydrogen-bonded interdigitated one-dimensional (11)) 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 ID 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 host-guest-host-host-guest-host- sequence infinitely. From time-dependent photoreaction studies, it has been found that the [2 + 2] photocycloaddition occurs between host-guest molecules first followed by host host 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 host and guest molecules. Further, solvothermal crystallization of the final photoproduct furnished an interesting three-dimensional CP with bcg topology. Interestingly, 2NO(2)-4spy also furnished a similar hydrogen-bonded ID 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.