Nickel pivalate complexes: structural variations and magnetic susceptibility and inelastic neutron scattering studies

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, [Ni-2(mu-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, [Ni-4(mu(3)-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, [Ni-4(mu(3)-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.