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.