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o c c a s i o n a l n o t e sT h e ne w e ngl a nd jou r na l o f m e dic i ne n engl j med 355;5 www.nejm.

A series of nickel complexes with nuclearity ranging from Ni(3) to Ni(6) have been obtained by treatment of a variety of nickel salts with the 2-pyridylcyanoxime ligand. The reported compounds have as a common structural feature the triangular arrangement of nickel cations bridged by a central μ(3)-oxo/alkoxo ligand. These compounds are simultaneously the first nickel derivatives of the 2-pyridylcyanoxime ligand and the first examples of isolated, μ(3)-O triangular pyridyloximate nickel complexes. Magnetic measurements reveal antiferromagnetic interactions promoted by the μ(3)-O and oximato superexchange pathways and comparison of the experimental structural and magnetic data with DFT calculations give an in-depth explanation of the factors that determine the magnetic interaction in this kind of system.

In the present work, coordination possibilities of the system dapdoH(2)/Ni(2+), being dapdoH(2) = 2,6-diacetylpyridine dioxime, have been explored, offering as a result a number of unprecedented clusters with a variety of topologies and magnetic behaviors. Depending on the precursors and reaction conditions, several compounds named [Ni(2)(dapdo)(2)] (1), [Ni(3)(OH)(BzO)(3)(dapdo)(dapdoH(2))(H(2)O)] x1.25 H(2)O (2), [Ni(3)(AcO)(4)(dapdoH)(2)(H(2)O)(2)] x H(2)O (3), and [Ni(4)(AcO)(3)(dapdo)(dapdoH)(2)(H(2)O)(3)] x (AcO) x 3 H(2)O (4) were achieved and structurally well-characterized. Dc magnetic measurements were carried out in the 2-300 K range revealing antiferromagnetic interactions for (2-4) compounds and diamagnetic response for the square planar coordinated complex (1).

In the present work, five new Ni5 clusters employing the versatile 2-pyridylcyanoxime ligand have been synthesized and chemically, structurally, and magnetically characterized. The crystallographic examination of these Ni5 clusters together with those already published in the literature, giving a total number of 14 complexes, exhibiting up to 8 different topologies for which the relationship between topology, reaction conditions and magnetic response has been analyzed. DC magnetic measurements were carried in the 300-2 K range for the new complexes and the analysis of the experimental data revealed an antiferromagnetic response for the oximato mediated interactions with a variety of ground states (S = 0, 1, 3) as function of the cluster topology.