Dinuclear Cu(II) Complexes of Isomeric Bis-(3- acetylacetonate)benzene Ligands: Synthesis, Structure, and Magnetic Properties

Highly versatile coordinating ligands are designed and synthesized with two ?-diketonate groups linked at the carbon 3 through a phenyl ring. The rigid aromatic spacer is introduced in the molecules to orient the two acetylacetone units along different angles and coordination vectors. The resulting para, meta, and ortho bis-(3-acetylacetonate)-benzene ligands show efficient chelating properties toward Cu(II) ions. In the presence of 2,2?-bipyridine, they promptly react and yield three dimers, 1, 2, and 3, with the bisacetylacetonate unit in bridging position between two metal centers. X-ray single crystal diffraction shows that the compounds form supramolecular chains in the solid state because of intermolecular interactions. Each of the dinuclear complexes shows a magnetic behavior which is determined by the combination of structural parameters and spin polarization effects. Notably, the para derivative (1) displays a moderate antiferromagnetic coupling (J = -3.3 cm-1) along a remarkably long Cu···Cu distance (12.30 Å).