Contrasting magnetic properties: Two isostructural metal-azido magnetic chains embedded in 3D threefold interpenetrated H-bonded frameworks and separated by a long bpeado spacer have been assembled (see figure). Incorporation of Mn2+ displays a rarely observed antiferromagnetic Heisenberg chain, while incorporation of Co2+ displays a ferromagnetic Ising chain.
We present here the structures and magnetism of two isostructural magnetic metal-azido chain compounds of the type [M(N3)2(H2O)2]⋅(bpeado) (1, M=Mn; 2, M=Co; bpeado=1,2-bis(4-pyridyl)ethane-N,N′-dioxide), prepared by utilizing the long spacer bpeado. The structure is composed of [M(N3)2(H2O)2]n metal-azido chains, in which metal ions are bridged by two end-on azido ligands, and the chains are further supported by H-bonding interactions between the coordination water of the chain and the lattice bpeado in a three-dimensional (3D) threefold interpenetrated H-bonded framework. Within the structure, the metal-azido chains are separated quite well. Investigation of the magnetic properties has revealed that the Mn compound 1 is an isotropic Heisenberg chain with unusual antiferromagnetic coupling between the Mn2+ ions linked by double end-on azide anions. The Co compound 2 shows a strong anisotropic Ising-type ferromagnetic chain within the material. Detailed magnetic studies on both polycrystalline and single-crystal samples of 2 have revealed a large coercivity of up to 37.5 kOe (along the crystallographic b-axis), multi-magnetic transitions, and single-chain-magnet-like magnetic relaxation behavior.
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