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 β-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 bis-acetylacetonate
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).