Post-synthetic modification of divalent nickel acetate cubanes with carboxylates

Dedicated to Professor Rudi van Eldik on the occasion of his 70th birthday.

Abstract

Starting from nickel(II) cubane [Ni^II₄(HL)₄(OAc)₄] (2a), five different tetranuclear cubic complexes [Ni^II₄(HL)₄(O₂CR)₄] (3) were generated simply by applying a post-synthetic cubane modification strategy via a complete acetate-to-carboxylate co-ligand exchange. This was achieved by stirring the parent complex 2a with a large excess of the corresponding sodium carboxylate salt 4 for three days in THF. Single-crystal X-ray structure analyses of Ni^II cubanes 3a·2 Et₂O and 3b·0.5 CH₂Cl₂·0.5 Et₂O reveal unequivocally that both are isostructural in terms of the [Ni₄(μ₃-O₄]⁴⁺ core and crystallize in the triclinic space group P-1 with two molecules in the unit cell. In the solid state, the cubic centers of 3a,b differ only slightly in bond lengths and angles mainly due to the different substituents in the carboxylate co-ligand and packing in the unit cell. The orientation of 3a,b and the formation of supramolecular aggregates in the crystal packing were controlled by π–π interactions as well as intra- and intermolecular O–H⋯O hydrogen bonds. Variable-temperature magnetic susceptibility measurements reveal that 3a–c show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for all investigated complexes.

Keywords:

• N, O ligands
• carboxylate ligands
• cubanes
• nickel
• post-synthetic modification

Acknowledgements

We also thank M.Sc. Maximilian Dürr and Prof. Ivana Ivanović-Burmazović for recording ESI-MS spectra.

Notes

Dedicated to Professor Rudi van Eldik on the occasion of his 70th birthday.