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Single-Crystal to Single-Crystal Structural Transformation and Photomagnetic Properties of a Porous Iron(II) Spin-Crossover Framework

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posted on 05.03.2008, 00:00 by Suzanne M. Neville, Gregory J. Halder, Karena W. Chapman, Martin B. Duriska, Peter D. Southon, John D. Cashion, Jean-François Létard, Boujemaa Moubaraki, Keith S. Murray, Cameron J. Kepert
The porous coordination framework material, Fe(NCS)2(bped)2·3EtOH, SCOF-3(Et) (where bped is dl-1,2-bis(4‘-pyridyl)-1,2-ethanediol), displays a spin-crossover (SCO) transition that has been stimulated both thermally and by light irradiation. The one-step thermal SCO (70−180 K) is sensitive to the presence of molecular guests, with a more gradual transition (70−225 K) apparent following the desorption of ethanol molecules that hydrogen bond to the spin centers. Additional intraframework hydrogen-bonding interactions stabilize the vacant one-dimensional pore structure of the apohost, SCOF-3, despite a dramatic single-crystal to single-crystal (SC−SC) structural change upon removal of the guests. Comprehensive structural analyses throughout this transformation, from primitive orthorhombic (Pccn) to body-centered tetragonal (I4/mcm), reveal a flexing of the framework and a dilation of the channels, with an accompanying subtle distortion of the iron(II) coordination geometry. Photomagnetic measurements of the light-induced excited spin state trapping (LIESST) effect have been used to assess the degree of cooperativity in this system.