Structure and EPR spectra of binuclear copper(II) complexes with acyldihydrazones of benzenedicarboxylic acids and 5-substituted 2-hydroxyacetophenones

Binuclear copper(II) complexes with acyldihydrazones of 1,3- or 1,4 benzenedicarboxylic acid and 5-methyl- or 5-bromo-2-hydroxyacetophenone in which coordination polyhedra are connected by an aromatic bridge have been synthesized and studied. The structure of the copper(II) complex with diacylhydrazone of isophthalic acid and 2-hydroxy-5-methylacetophenone (H₄L) of composition [Cu₂L · 3Py] was studied by X-ray diffraction. The crystals are monoclinic: a = 12.1996(12) Å, b = 17.7295(17) Å, c = 17.9339(17) Å, β = 109.7450(10)°, space group P2₁/n, Z = 4. The complex is of the “dimer of dimers” type and contains two binuclear subunits that bind together into a centrosymmetric dimer owing to the coordination of the copper cation to the phenoxyl oxygen atom of a neighboring binuclear molecule to form the Cu₂O₂ moiety, in which the copper atoms are 3.409 Å apart. The distance between the copper(II) cations in the binuclear subunit is 8.56 atoms (2N + O) of the doubly deprotonated acylhydrazone moiety and the nitrogen atom of the pyridine molecule. One of the copper cation is additionally coordinated to an extra pyridine molecule so that its coordination sphere is completed to a tetragonal pyramid. The second copper atom is involved in additional interaction with the phenoxyl oxygen atom of the neighboring molecule. The EPR spectra of solutions of the binuclear complexes show an isotropic signal of four HFS lines (g _o = 2.065–2.143, a _Cu = 52.1–66.5 × 10^?4 cm^?1) typical of mononuclear copper(II) complexes.