Syntheses, structures, and magnetic properties of cyano-bridged heterobimetallic complexes based on [Fe(bpca)(CN)₃]^-

Two new cyano-bridged one-dimensional heterobimetallic coordination polymers, [(bpca)₂Fe^III₂(CN) ₆Cu(H₂O)₂·1.5H₂O] _n (2) and [(bpca)Fe^III(CN)₃Cu(bpca)(H ₂O)·H₂O]_n (3), and a trinuclear complex, [(bpca)₂Fe^III₂(CN)₆Mn(CH ₃OH)₂(H₂O)₂]·2H₂O (4), have been synthesized using the tailored tricyanometalate precursor (Bu₄N)[Fe(bpca)(CN)₃]·H₂O (1) (Bu ₄N⁺ = tetrabutylammonium cation; bpca = bis(2-pyridylcarbonyl)amidate anion) as a building block and structurally characterized. In complex 2, the Cu^II ions are six-coordinated in an elongated distorted octahedral environment, and they are linked by distorted octahedrons of [Fe(bpca)(CN)₃]^- to form 1D chain of squares. Complex 3 is an unexpected chiral heterobimetallic helical chain complex, in which the helical chain consists of the asymmetric unit of [(bpca)Fe(CN)₃Cu(bpca)(H₂O)]. In complex 4, there are two independent trinuclear clusters in one asymmetric unit, and the coordination modes of the two methanol and two water molecules coordinating to the central Mn(II) ion are different (cis and trans). Complex 2 shows metamagnetic behavior with a Neel temperature of T_N = 2.2 K and a critical field of 250 Oe at 1.8 K, where the cyanides mediate the intrachain ferromagnetic coupling between the Cu^II and Fe^III ions. Complex 3 shows ferromagnetic coupling between Cu^II and Fe^III ions, the best-fit for χ_MT versus T using a 1D alternating chain model leads to the parameters J₁ = 7.9(3) cm^-1, J₂ = 1.03(2) cm^-1, and g = 2.196(3). Complex 4 exhibits ferrimagnetic behavior caused by the noncompensation of the local interacting spins (S _Mn = 5/2 and S_Fe = 1/2) which interact antiferromagnetically through bridging cyano groups.