Tunable Assembly and Magnetic Interactions in Two Cyano-bridged Fe III –Co II Bimetallic Complexes

Using a new semi-rigid tetradentate ligand and two cyanometalate building blocks with different steric hindrance, a Fe 2 Co triangular unit [(Tp)Fe III (CN) 3 ] 2 Co II (bpmb)·2H 2 O [ 1 ; Tp = hydrotris(pyrazolyl)borate; bpmb = 1,2-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzenes] and a Fe 2 Co 2 square unit {[(pzTp)Fe III (CN) 3 ] 2 [Co II (bpmb)] 2 }·[(pzTp)Fe III (CN) 3 ] 2 ·4H 2 O [ 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)Fe III (CN) 3 ] − compared with [(Tp)Fe III (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 Fe III and Co II 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 Fe III and Co II ions and Co–N≡C bond angles.