Spin Crossover Behavior of FeII Complexes Bridged by Thiophene‐Functionalized Triazole Ligands with Different Sizes and Rigidities

Abstract

AbstractFour thiophene functionalized triazole ligands (L1=4‐(thenyl)‐1,2,4‐triazole, L2=4‐(thiophene ethyl)‐1,2,4‐triazole, L3=N‐Thiophenylidene‐4H‐1,2,4‐triazole‐4‐amine, and L4=(4‐[(E)‐2‐(5‐sulfothiophene)vinyl]‐1,2,4‐triazole) were synthesized. These ligands have different lengths and rigidities, while ligand L4 has a sulfonic acid group that can form a hydrogen bond. Five 1D FeII chain complexes were synthesized: [Fe(L1)3](X)2 ⋅ nH2O [X=BF4−, n=1.5 (C1); X=ClO4−, n=1 (C2)], [Fe(L2)3](BF4)2 ⋅ 1.5H2O (C3); [Fe(L3)3](X)2 ⋅ nH2O [X=BF4−, n=2 (C4); X=ClO4−, n=2.5 (C5)]. The results of temperature‐dependent magnetic susceptibility reveal that complexes C1, C2, and C3 experienced the transition between two spin states. And C4 and C5 maintain high spin states at all temperature ranges. Binuclear complex [Fe2(L3)5(SCN)4] (C6) and mononuclear material [Fe(L4)2(H2O)4] ⋅ 2H2O (C7), these two zero‐dimensional molecules were also synthesized. They all display weak antiferromagnetic exchange coupling and a high spin state in the whole process.