Solid‐state 2 + 2 photocycloaddition in an interpenetrated Mn( II )‐based metal–organic framework via a single‐crystal‐to‐single‐crystal transformation

Abstract Metal–organic frameworks (MOFs) are structurally tunable crystalline materials that can undergo stimulus‐induced transformations in the solid state. Herein, we report a light‐induced manganese(II)‐based MOF, Mn(bpe)(tdc)·2DMA ( 1 ), incorporating olefinic 1,2‐bis(4‐pyridyl)ethylene (bpe) ligands. MOF 1 crystallizes in the monoclinic C 2/ c space group and features Mn(II) centers with distorted octahedral coordination geometries. The yellow block‐shaped crystals adopt a double‐pillared pcu topology with parallel alignment of bpe ligands, in which the olefinic CC bonds are separated by 4.016 Å, satisfying Schmidt's criteria for solid‐state 2 + 2 photocycloaddition. Upon ultraviolet irradiation, MOF 1 undergoes a 2 + 2 photocycloaddition reaction to form Mn 2 ( rctt ‐tpcb)(tdc) 2 ·2DMA ( 2 ). Single‐crystal X‐ray diffraction analysis confirms the formation of cyclobutane rings in MOF 2 while preserving the pcu topology, parallel two‐fold interpenetration, and overall crystallinity. Despite the covalent bond formation and structural rearrangement, the coordination environments of the Mn(II) centers remain intact. This work demonstrates a rare example of a single‐crystal‐to‐single‐crystal photochemical transformation in a Mn(II)‐based MOF and highlights the potential of rational structural design for controlling solid‐state photoreactivity.