Hard magnets based on transition metal complexes with the dicyanamide anion, {N(CN)2}-

We present the crystal structures and magnetic properties of a series of magnetic compounds, M-II{N(CN)(2)}(2), where M = Cu (1), Ni (2), Co (3) and Fe (4), and [Mn{N(CN)(2)}(2)(C2H5OH)(2)]Z .(CH3)(2)CO (5). In the isostructural compounds 1-4, the dicyanamide anion is triply coordinating through its three nitrogen atoms. It bridges the metal ions to form infinite 3D metal-organic frameworks with a rutile-type structure. The framework contains doubly bridged M(-N=C-N-C=N-)(2) ribbons that link approximately orthogonally through the amide nitrogen atoms. The Jahn-Teller distortion in 1 has a strong influence on the packing arrangement (M-N bond lengths: 1.98 and 2.47 Angstrom for 1 and 2.10 and 2.15 Angstrom for 3). On lowering the temperature the bond distances in 1 remain unchanged except for a decrease of the M-N-amide length to 2.45 Angstrom Magnetic data for 1 obey the Curie-Weiss law (Theta = -2.1 K). 2 and 3 are ferromagnets with Curie temperatures (T-c) of 9 and 21 K and are characterized by hysteresis loops of 710 and 7975 Oe at 2 K, remnant magnetization, magnetization approaching the expected saturation (gS) of 2 and 3 mu(B) in high field, absorptive component (chi ") in the AC magnetization and lambda peak in the heat capacity data. 4 is similarly characterized and shows behaviour that is characteristic of a canted antiferromagnet: the Weiss constant is temperature dependent (+ 3 K in the range 200-300 K), there is a sharper peak than for 1 or 2 in the AC magnetization and the isothermal magnetization at 3 K increases monotonically to approximate to 1.3 mu(B) (expected to be 4 mu(B) for ferromagnetic alignment of the spins) in a field of 8 T. Its coercive field (17 800 Oe) is the largest observed for any metal-organic compound and exceeds those of alloys of SmCo5 and Nd2Fe14B. The maximum energy product (B . H) is the highest for 3 and is comparable to alloys of Sm-Co. We attribute the large coercive held to a combination of single ion and particle shape anisotropies. 5 is paramagnetic at high temperature with Theta = -3 K. Below 16 K it behaves as a canted antiferromagnet with a very weak resultant spontaneous magnetization.