Dimensionality-Dependent Solid-State Photoreactivity in Zn(II)-Based Coordination Assemblies Featuring a Single-Crystal-to-Single-Crystal Transformation

Metal–organic frameworks (MOFs) are attractive platforms for controlling solid-state reactivity owing to their tunable structures and well-defined architectures. Herein, we report a discrete Zn(II) coordination complex (1) and a one-dimensional Zn(II)-based coordination assembly (2) constructed from 4-styrylpyridine (spy) and 4,4′-sulfonyldibenzoate (sdb) ligands, which exhibit distinct solid-state photoreactivities depending on their structural dimensionality and ligand alignment. Compound 1 forms a zero-dimensional discrete complex in which the olefinic spy ligands are arranged in a nonparallel manner with large separations, resulting in photoinert behavior under UV irradiation. In contrast, compound 2 adopts a one-dimensional framework in which neighboring olefin groups are aligned in a parallel head-to-tail fashion with an intermolecular distance of 3.6 Å, satisfying Schmidt’s criteria for solid-state [2 + 2] photocycloaddition. Upon UV irradiation, compound 2 undergoes a partial photodimerization of the spy ligands (50%) to afford a cyclobutane-containing product, [Zn2(rctt-ppcb)0.5(spy)(sdb)2]·H2O (3) (where rctt-ppcb is regio, cis, trans, trans; ppcb = 1,3-bis(4′-pyridyl)-2,4-bis(phenyl)cyclobutane), via a single-crystal-to-single-crystal transformation. The formation of the cyclobutane ring in 3 was unambiguously confirmed by single-crystal X-ray diffraction analysis. These results demonstrate that structural dimensionality and ligand alignment play decisive roles in governing solid-state photoreactivity in Zn(II)-based coordination assemblies.