A μ ₃-alkoxo-bridged tetranuclear [Cu ₄L ₂] copper(II) complex of a hexadentate N₂O₄ donor ligand with a [6 + 0] Cu₄O₄ cubane core: Synthesis, crystal structure, and magnetic properties

A novel hexacoordinating non-Schiff base ligand (H ₄L) with N ₂O ₄ donor atoms has been synthesized by simple Mannich reactions. The use of this ligand with Cu(ClO ₄) ₂* 6H ₂O in different molar ratios as well as pH leads to the formation of a mononuclear species and a tetranuclear CuII complex possessing a cubane [Cu ₄L ₂] core with almost equal Cu...Cu separation. In the presence of an excess amount of copper(II) ions and triethylamine at reflux, the mononuclear [CuH ₂L] species can be converted into the tetranuclear one, whereas the reverse process was not observed even after prolonged reaction time. Both the complexes have been characterized by single-crystal X-ray diffraction and magnetic measurements. Magnetic studies reveal that complex 1 displays a paramagnetic Curie-type behavior whereas 2 displays a singletspin ground state induced by strong intramolecular antiferromagnetic interactions.