Topochemical [2 + 2] Cycloaddition in a Two-Dimensional Metal-Organic Framework via SCSC Transformation Impacts Halogen···Halogen Interactions.

A photoactive two-dimensional metal-organic framework (2D MOF) [Zn(4-spy)(DCTP)]n (1) [where 4-spy = 4-styrylpyridine and H2DCTP = 2,5-dichloroterephthalic acid] undergoes photochemical [2 + 2] cycloaddition on UV irradiation to obtain three-dimensional (3D) MOF [Zn(rctt-4-ppcb)(DCTP)]n (2) [rctt-4-ppcb = 1,3-bis(4'-pyridyl)-2,4-bis(phenyl)cyclobutane] in a single-crystal to single-crystal (SCSC) manner. This structural transformation leads to stronger halogen···halogen interaction that is well-corroborated by density functional theory (DFT) calculations.