A Two-Dimensional Iron(II) Coordination Polymer with Synergetic Spin-Crossover and Luminescent Properties

A composite material, {[Fe(L)(TPPE)(0.5)].3CH(3)OH}(n), has been constructed by integrating the spin-crossover (SCO) subunit Fe-II{diethyl(E,E)-2,2 '-[1,2-phenyl-bis(iminomethylidyne)]bis(3-oxobutanoate)-(2-)-N,N ',O-3,O-3 '} and the highly luminescent connector 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)-ethene. Its structure contains four staggered 4x4 layers and intercalated methanol. The packing is dominated by considerable H-bonds either between adjacent layers and between layers and guests. A crystal-structure transformation was detected upon removal of the guest molecules. The SCO transition of the solvated crystals is centered at ca. 215K with a non-symmetrical hysteresis of 25K wide, and the desolvated [Fe(L)(TPPE)(0.5)](n) exhibits gradual SCO without hysteresis. Intriguingly, the intensity of the fluorescence at 460nm for the latter is maximized at the SCO transition. The energy transfer between luminescent and SCO entities is achievable as confirmed by theoretical calculations.