Modulation of Spin-Crossover Behavior in an Elongated and Flexible Hofmann-Type Porous Coordination Polymer

Three porous coordination polymers {Fe(dpa)[Pt(CN)(4)]center dot G center dot nH(2)O} (1-G; dpa = 1,2-di(4-pyridyl)ethane, G = dpa, bibenzyl (bbz) and stilbene (stb)) have been prepared by using a long and flexible ligand dpa. These compounds formed analogous 3-D elongated Hofmann-type frameworks based on 2-D planar layers extended by Pt-CN-Fe linkages with dpa as flexible pillar ligands. 1-dpa showed a characteristic three-step spin transition (ST) in the temperature range 180-240 K. The ST behavior was reversibly modulated by dehydration and hydration processes in keeping with the three steps. 1-bbz and 1-stb exhibited a gradual three-step ST over the range 80-200 K and an abrupt ST with T (c) = 163 K. The guest-dependent cooperativity of the ST behavior is discussed by considering the flexibility of the framework and guest molecules.