An Ni<INF>4</INF> Single-Molecule Magnet: Synthesis, Structure and Low-Temperature Magnetic Behavior

The reaction of Ni(NO<INF>3</INF>)<INF>2</INF>·6H<INF>2</INF>O with H<INF>3</INF>thme (trihydroxymethylethane) in the presence of NaOMe leads to a tetranuclear Ni<INF>4</INF> complex with a cubane-like structure. Intramolecular ferromagnetic interactions [J = 10 cm⁻¹ based on H = −J(S<INF>1</INF>·S<INF>2</INF> + S<INF>1</INF>·S<INF>3</INF> + S<INF>1</INF>·S<INF>4</INF> + S<INF>2</INF>·S<INF>3</INF> + S<INF>2</INF>·S<INF>4</INF> + S<INF>3</INF>·S<INF>4</INF>)] lead to an S = 4 ground state stabilized by 40 cm⁻¹ from the first S = 3 excited state. Magnetization vs. field studies at different temperatures above 2 K suggest the presence of an axial magnetic anisotropy. Single-crystal magnetization measurements show a single-molecule-magnetic behavior below T = 0.5 K with fast relaxation of the magnetization due to resonant quantum tunneling. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)