Synthesis, structure and magnetism of a low-symmetry [Ni4O4] cubane derived from di-2-pyridyl ketone and isophthalic acid and magnetostructural correlation

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 (py2CO) and isophthalic acid (H2bdc), we isolated a new tetranuclear complex with a low-symmetry [Ni4O4] cubane core and pending RCOOH/RCOO- groups, namely [Ni4{py2CO(OH)}4(bdc)(Hbdc)2]0.5H2O (1), (py2C(OH)2 is the hydrate of py2CO). In this distorted [Ni4(mu 3-OR)4]4+, which comprises the deprotonated O atoms of the py2C(OH)O- ligands, one of the six NiNi distances is relatively short (2.965 & Aring;) with the rest ranging from 3.029 - 3.292 & Aring;. The six [Ni2O2] faces of the cube are divided in three pairs of opposite faces, with large (similar to 103 degrees) and small (similar to 93.2 degrees) Ni-O-Ni angles, and one pair with a small and a large Ni-O-Ni angle. A 3-J-model was demanded to fit the temperature dependence of the magnetic susceptibility. Magnetostructural correlations among all known NiII tetranuclear clusters comprising a [Ni4O4] cubane core have also been performed.