Tunable Assembly and Magnetic Interactions in Two Cyano-bridged FeIII–CoII Bimetallic Complexes

Abstract

Using a new semi-rigid tetradentate ligand and two cyanometalate building blocks with different steric hindrance, a Fe2Co triangular unit [(Tp)FeIII(CN)3]2CoII(bpmb)·2H2O [1; Tp = hydrotris(pyrazolyl)borate; bpmb = 1,2-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzenes] and a Fe2Co2 square unit {[(pzTp)FeIII(CN)3]2[CoII(bpmb)]2}·[(pzTp)FeIII(CN)3]2·4H2O [2; pzTp = tetrakis(pyrazolyl)borate] were synthesized via tunable assembly. Both compounds adopt cis arrangement because of the structural distorted semi-rigid bpmb. Tetranuclear square of 2 was formed due to larger steric hindrance building block of [(pzTp)FeIII(CN)3]− compared with [(Tp)FeIII(CN)3]− in trinculear 1. Magnetic measurements show that antiferromagnetic interactions dominate in 1 and 2. The fitting results of J values suggest a positive correlation between magnetic orbitals overlap of FeIII and CoII ions and Co–N≡C bond angles. Graphical Abstract Two cis arrangement cyanometalate [Fe-Co] clusters were synthesized via tunable assembly with a new semi-rigid tetradentate ligand. The tetranuclear cluster was formed because of larger steric hindrance of pzTp. Both compounds exhibit dominant antiferromagnetic couplings. The fitting results of J values suggest a positive correlation between magnetic orbitals overlap of FeIII and CoII ions and Co–N≡C bond angles.