Synthesis, structure and magnetism of three cubane Cu(II) and Ni(II) complexes based on flexible Schiff-base ligands

Three cubane Ni(II) and Cu(II) complexes, namely [Cu4L14]·CH3CN (1), [Ni4L14(CH3OH)4]·4H2O (2), [Ni4L24(CH3OH)4]·6H2O (3), have been synthesized from flexible polydentate Schiff bases (H2L1 and H2L2) based on o-vanillin. X-ray single-crystal analyses reveal that all three complexes own a cubane-like core M4O4 in which Cu ions in 1 are five-coordinated and Ni ions in 2 and 3 are six-coordinated. Variable-temperature magnetic susceptibility data display dominant ferromagnetic interactions in complexes 1–3 while antiferromagnetic and ferromagnetic couplings coexist in the cubane core, thus resulting in a nonzero spin ground state. The magnitude of the exchange coupling constants correlates with the geometrical parameters arising from the minor ligand modifications.