Enhanced dielectricity coupled to spin-crossover in a one-dimensional polymer iron(ii) incorporating tetrathiafulvalene

In designing multifunctional materials for potential switches that can be used as memory devices, the high-spin (HS) to low-spin (LS) crossover (SCO) one-dimensional polymer, [Fe-II(L)(4,4 '-bpy)](n), was constructed from a designed redox-active tetrathiafulvalene (TTF) functionalized Schiff-base and the ditopic linker 4,4 '-bipyridine (bpy). It exhibits an 8 K hysteretic SCO centred atT(1/2)= 325 K which is coupled to changes in its dielectric constant. The crystal structures above and below the transition temperature reveal similar parallel linear MIDLINE HORIZONTAL ELLIPSISFe-bpy-Fe-bpyMIDLINE HORIZONTAL ELLIPSIS chains displaying expansion of the Fe(II)octahedron in the HS state. Density functional theory (DFT) calculations reveal a concerted electronic charge and spin change represented by the Mulliken charge of the Fe and the magnitude and direction of the dipole moment which substantiate the experimental observations.