Locking the spin states of anionic Fe(L) 2 units in coordination polymers through alkali metal ion incorporation

units, as confirmed by octahedral distortion parameter analysis of compounds 1-3 and magnetic susceptibility measurements for compounds 1-2. In DMSO solution, all three compounds undergo similar SCO behavior with nearly identical transition temperatures, ascribed to the fact that the solution-phase magnetism is governed by the intrinsic ligand field. This work clearly demonstrates that the spin state of a mononuclear SCO-active unit in the solid state can be effectively and predictably controlled through the strategic introduction of a second coordination metal ion located outside the SCO core, providing a novel design strategy for functional molecular materials with tailored magnetic properties.