Syntheses, crystal structures, and magnetic properties of a series of cyanide-bridged trinuclear chromate(III)−nickel(II)−chromate(III) complexes based on dicyanidechromate(III) building blocks

Four cyanide-bridged trinuclear CrIII−NiII−CrIII complexes [Ni(cyclam)][Cr(bpb)(CN)2]2·2H2O (1) (cyclam = 1,4,8,11-tetraazacyclotetradecane, bpb2– = 1,2-bis(pyridine-2-carboxamido)-benzenate), [Ni(cyclam)][Cr(bpClb)(CN)2]2·4H2O (2) (bpClb2– = 1,2-bis(pyridine-2-carboxamido)-4-chloro-benzenate), [Ni(cyclam)][Cr(bpmb)(CN)2]2·4H2O (3) (bpmb2– = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate) and [Ni(cyclam)][Cr(bpdmb)(CN)2]2 (4) (bpdmb2– = 1,2-bis(pyridine-2-carboxamido)-4,5-dimethyl-benzenate) have been synthesized by the reaction of [Ni(cyclam)](ClO4)2 with a series of dicyanidechromate(III) building blocks. Single crystal X-ray diffraction analyses show that the four complexes have similar trinuclear structures with CrIII–CN–NiII–NC–CrIII linkages. Magnetic investigations indicate the ferromagnetic coupling between Cr(III) and Ni(II) centers through the cyanide bridge, with JCrNi = 4.64(3) cm−1 for 1, 4.33(4) cm−1 for 2, 3.57(3) cm−1 for 3 and 5.3(1) cm−1 for 4. The study on magneto-structural correlation for cyanide-bridged CrIII−NiII systems reveals that the cyanide-bridging bond angle is related to the strength of magnetic exchange coupling: the larger the Ni–NC bond angle, the stronger the Ni⋯Cr magnetic interaction.