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

• Published in: Chemical science (Cambridge) 2020-06, Vol.11 (24), p.6229-6235
• Main Authors: Qiu, Ya-Ru, Cui, Long, Cai, Pei-Yu, Yu, Fei, Kurmoo, Mohamedally, Leong, Chanel F, D'Alessandro, Deanna M, Zuo, Jing-Lin
• Format: Article
• Language: English
• Subjects: Crossovers; Crystal structure; Crystallography; Density functional theory; Dipole moments; Electron spin; Imines; Iron; Memory devices; Multifunctional materials; Polymers; Switches; Transition temperature
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d0sc02388d

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 at T 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 Fe-bpy-Fe-bpy 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 Mülliken charge of the Fe and the magnitude and direction of the dipole moment which substantiate the experimental observations. A concerted bending-flattening motion of the redox-active TTF within constructed one-dimensional Fe II -TTF-Schiff-base chain with bridging 4,4′-bpy enhances the dielectric constant coupled to its spin-crossover transition above room temperature.