Synthesis, structure and magnetism of a low-symmetry [Ni<sub>4</sub>O<sub>4</sub>] cubane derived from di-2-pyridyl ketone and isophthalic acid and magnetostructural correlation
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In an attempt to expand our “mixed-ligand” synthetic approach for the isolation of new coordination polymers from the simultaneous use of di-2-pyridyl ketone (py<sub>2</sub>CO) and isophthalic acid (H<sub>2</sub>bdc), we isolated a new tetranuclear complex with a low-symmetry [Ni<sub>4</sub>O<sub>4</sub>] cubane core and pending RCOOH/RCOO<sup>–</sup> groups, namely [Ni<sub>4</sub>{py<sub>2</sub>CO(OH)}<sub>4</sub>(bdc)(Hbdc)<sub>2</sub>]·0.5H<sub>2</sub>O (<b>1</b>), (py<sub>2</sub>C(OH)<sub>2</sub> is the hydrate of py<sub>2</sub>CO). In this distorted [Ni<sub>4</sub>(μ<sub>3</sub>-OR)<sub>4</sub>]<sup>4+</sup>, which comprises the deprotonated O atoms of the py<sub>2</sub>C(OH)O<sup>–</sup> ligands, one of the six Ni···Ni distances is relatively short (2.965 Å) with the rest ranging from 3.029 − 3.292 Å. The six [Ni<sub>2</sub>O<sub>2</sub>] faces of the cube are divided in three pairs of opposite faces, with large (∼103°) and small (∼93.2°) Ni-O-Ni angles, and one pair with a small and a large Ni-O-Ni angle. A 3-<i>J</i>-model was demanded to fit the temperature dependence of the magnetic susceptibility. Magnetostructural correlations among all known Ni<sup>II</sup> tetranuclear clusters comprising a [Ni<sub>4</sub>O<sub>4</sub>] cubane core have also been performed.
