Coordination-Induced Spin State Switching via a Crystal-to-Crystal Transformation of Dynamic Coordination Polymers

In this study, coordination-induced spin state switching (CISSS) functionality was achieved through a dynamic coordination polymerization process. A discrete grid [Ni₄(hnih)₄(py)₈]·6MeOH (1·py) based on a nitro-decorated isonicotinoylhydrazide ligand underwent ring-opening coordination polymerization into three one-dimensional chains [Ni(hnih)(py)₂·py]_n (2·py), [Ni(hnih)(DMSO)₂·DMSO]_n (2·DMSO), and [Ni(hnih)]_n (2), of which the transformation involved coordination sphere rearrangement and topologic change. Optical and magnetic studies demonstrated that the reversible high spin (HS) ↔ low spin (LS) transitions can be achieved in the solid state between the octahedral species (1·py, 2·py, and 2·DMSO) and the square planar complex 2 via a CISSS process. This work introduces a crystal-transformation-driven strategy to achieve and regulate CISSS functionality in dynamic coordination polymers, paving the way for solid-state stimuli-responsive materials.