Influence of Halogen Atoms on Spin‐Crossover Properties of 1,2,4‐Triazole‐Based 1D Iron(II) Polymers

Abstract

AbstractThe introduce of halogen atoms (F, Cl, Br, I) to the triazole‐based ligand N‐benzyl‐4‐amino‐1, 2, 4‐triazole (L) have shown a significant effect on the spin‐crossover (SCO) properties of the corresponding one‐dimensional (1D) coordination Fe (II) polymers with chemical formula [Fe(4‐X–L)3](BF4)2 (X=F, Cl, Br, and I). Compared with the [FeL3](BF4)2, the electronegative halogen atoms have increased the π‐acceptor character of these ligands, which thus improved the ligand field strength and induced the occurrence of SCO for the Fe (II) polymers at higher temperatures. The SCO transition temperatures T1/2 have changed from 200 K to 249 (I), 250 (Br), 252 (Cl) and 275 (F) K, respectively. More importantly, the UV‐Vis absorption spectrum and density functional theory (DFT) calculations indicated that the transition temperatures and the width of thermal hysteresis loops have shown a positive correlation with the electronegativity of the halogen atoms.