Grégory Chaboussant, Reto Basler, Hans-Ulrich Güdel, Stefan Ochsenbein, Andrew Parkin, Simon Parsons, Gopalan Rajaraman, Andreas Sieber, Andrew A. Smith, Grigore A. Timco and Richard E. P. Winpenny
Nickel pivalate complexes: structural variations and magnetic susceptibility and inelastic neutron scattering studies
Dalton Trans. 2758-2766 (2004)                 

Abstract: The synthesis and structural characterisation of three small nickel(II) cages are reported, all stabilised by pivalate ligands. The magnetic properties of the cages have been studied by a combination of susceptibility measurements and inelastic neutron scattering. For a dinuclear cage, [Ni₂(m-OH₂)(O₂CCMe₃)₄(HO₂CCMe₃)₄] 1 the ground state is S = 2, with a ferromagnetic exchange interaction between the Ni(II) centres of J = 0.32 meV and D_S=2 = –0.09 meV in the ground state. For a tetranuclear heterocubane cage, [Ni₄(m₃-OMe)₄(O₂CCMe₃)₄(MeOH)₄] 2, two ferromagnetic exchange interactions are found and an S = 4 ground state observed. While the zero-field splitting of this state cannot be determined unambigiously the most likely value is D_S=4 = –0.035 meV. For a tetranuclear nickel butterfly, [Ni₄(m₃-OH)₂(O₂CCMe₃)₆(EtOH)₆] 3, three exchange interactions are required, two anti-ferromagnetic and one weakly ferromagnetic; the resulting ground state is S = 0. The data enable us to estimate the zero-field splitting of single Ni(II) ions involved in the cage as D_i = +1.0 meV. Both 1 and 2 are therefore expected to be new single molecule magnets.