Single crystal to single crystal [2+2] photoreactions in chloride and sulphate salts of 4-amino-cinnamic acid via solid-solution formation: a structural and kinetic study.

A set of molecular salts with general formula [1H]nA·xH2O (1 = 4-amino-cinnamic acid, A(n-) = NO3(-), BF4(-), PF6(-), SO4(2-), x = 0, 1) was prepared and structurally characterized. [1H]Cl and [1H]2SO4·H2O(II) were found to undergo an SCSC stepwise [2+2] photodimerization, which was followed by X-ray diffraction; a kinetic analysis was performed on single crystals of both salts. In the case of [1H]Cl the photoreaction was also studied on polycrystalline materials.