Novel Co(5) and Ni(4) Metal Complexes and Ferromagnets by the Combination of 2-Pyridyl Oximes with Polycarboxylic Ligands

The use of 2-pyridyl oximes in metal complexes chemistry has been extensively investigated in the last few decades as a fruitful source of species with interesting magnetic properties. In this work, the initial combination of pyridine-2-amidoxime (pyaoxH(2)) and 2-methyl pyridyl ketoxime (mpkoH) with isonicotinic acid (HINA) and 3,5-pyrazole dicarboxylic acid (H(3)pdc) has provided access to three new compounds, [Ni(4)(INA)(2)(pyaox)(2)(pyaoxH)(2)(DMF)(2)] (1), [Co(5)(mpko)(6)(mpkoH)(2)(OMe)(2)(H(2)O)](ClO(4))(6) (2), and [Co(5)(OH)(Hpdc)(5)(H(2)pdc)] (3). 1 displays a square-planar metal topology, being the first example that bears simultaneously HINA and pyaoxH(2) in their neutral or ionic form. The neighbouring Ni(4) units in 1 are held together through strong intermolecular hydrogen bonding interactions, forming a three-dimensional supramolecular framework. 2 and 3 are mixed-valent Co(4)(III)Co(II) and Co(2)(III)Co(II)(3) compounds with a bowtie and trigonal bipyramidal metal topology, accordingly. Direct current and alternate current magnetic susceptibility studies revealed that the exchange interactions between the Ni(II) ions in 1 are ferromagnetic (J = 1.79(4) cm(−1)), while 2 exhibits weak AC signals in the presence of a magnetic field. The syntheses, crystal structures, and magnetic properties of 1–3 are discussed in detail.