Hydrothermal synthesis, structures and magnetic studies of transition metal sulfates containing hydrazine.

By employing hydrothermal method, six transition metal sulfates containing hydrazine (N(2)H(4)) have been obtained: [M(SO(4))(2)(N(2)H(5))(2)](n) (M = Mn(1), Co(2), Ni(3)) and [M(N(2)H(4))SO(4)](n) (M = Mn(4), Co(5), Ni(6)). Their crystal structures and magnetic properties have been investigated experimentally and theoretically. Compounds 1-3 consist of one-dimensional sulfate bridged homometallic chains with protonated hydrazine molecule as terminal ligand, and compounds 4-6 are hydrazing-sulfate mixed bridged homometallic three-dimensional frameworks. Compounds 1-6 exhibit antiferromagnetic coupling between M(2+) ions, but their magnetic properties differ at low temperatures because of the different single-ion anisotropy and crystal structures. The magnetostructural correlations and the magnetic coupling mechanism are analyzed by density functional theory calculations (DFT).

Two EE-azido-bridged nickel(II) layered compounds: vigorous twisted torsion angle Ni-N3-Ni results in ferromagnetic behavior.

Two coordination polymers, Ni(endi)(N(3))(2) (endi = 1,2-bis(tetrazol-1-yl)ethane) (1) and Ni(4-acpy)(2)(N(3))(2) (4-acpy = 4-acetylpyridine) (2), are obtained by employing a couple of cobalt complex as references. Both compounds have similar 2D (4,4) EE azide-nickel layer structures, but different interlayer separations. Their EE azide bridges are vigorously twisted, with the torsion angle tau value 88.3 degrees and 107.6 degrees for 1 and 89.2 degrees for 2. Different from most EE azide compounds, ferromagnetism is distinctly present, ordering below T(c) = 25 K for 1 and T(c) = 23 K for 2. Fitting of magnetic susceptibility data using the spin Hamiltonian H = -2J SigmaS(1)S(2) gives the ferromagnetic intralayer coupling J = 14.70(6) cm(-1) for 1 and 14.32(0) cm(-1) for 2, respectively. The magnetostructural correlations of 1 have been calculated using the density function theory based method. The computational results are consistent with the trend of the experimental data. One possible mechanism was proposed to explain the emergence of ferromagnetism based on the theoretical studies, and the ferromagnet construction approach was also proposed accordingly.

Synthesis, structure, and magnetism of three azido-bridged Co2+ compounds with a flexible coligand 1,2-(tetrazole-1-yl)ethane.

By utilizing suitable coligand endi (1,2-(tetrazole-1-yl)ethane)) with variable conformations, we synthesized three new azido-bridged Co(2+) compounds with molecular formulas Co(endi)(N3)2 (1, 3) and Co(endi)2(N3)2 (2) by tuning the stoichiometric ratio of ligand/metal and the concentration of the solution. All of the compounds have been characterized structurally and magnetically. In all three structures, the azide ions use the end-to-end mode to link the Co(2+) centers to the 1D chain (1) and 2D (4,4) layers (2 and 3). The endi coligands adopt a trans conformation in compound 1 and a gauche conformation in compounds 2 and 3. Linked by bridging endi, the 1D chains in compound 1 and 2D layers in compound 3 are extended, resulting in the final 2D layer for compound 1 and the 3D network for compound 3, whereas in compound 2, the endi acts as only a terminal ligand to separate the 2D layers. Compound 1 consists of dual end-to-end azido-bridged 1D Co(2+) chains that are linked by trans endi into a 2D layer and are further extended to a 3D framework through H bonds. Compound 2 is a 2D (4,4) layer that is connected by end-to-end azido ions. The gauche endi ligands act as terminal ligands to separate the neighboring layers thoroughly. Compound 3 has a (4,4) 2D layer that is similar to that of compound 2, and these layers are further extended to a 3D network through gauche endi. The magnetic investigation shows that compound 3 is antiferromagnetically coupled and compound 2 is a weak ferromagnet with a critical temperature of 22 K, which is quite high compared with that of the previously reported 2D azido-bridged Co(2+) compounds.