EPR spectra of and exchange interactions in trinuclear complexes. 3. Synthesis, crystal structure and magnetic properties of the oxovanadium(IV) adduct of a tetradentate Schiff base copper(II) complex

The complex ( C U H A P ~ ~ ) ~ V O ( C ~ O ~ ) ~ ~ ~wHhe~re OC-uH~A/Pe~nC is~ (NH,N~’-NetOhy~le,ne bis(0-hydroxyacetophenone iminato)) copper(II), was synthesized and its crystal structure solved at room temperature. It crystallizes in the orthorhombic system, space group P212121. The lattice constants are a = 20.928 (9) A, b = 20.065 (7) A, and c = 10.794 (9) A, with Z = 4. Least-squares refinement of the structure led to a conventional R factor of 0.052. The asymmetric unit comprises a dipositive trinuclear cation, two perchlorate anions, one water, and half of a nitroethane molecule. The two CuHAPen complex ligands bind to a central hexacoordinate oxovanadium(1V) occupying nonequivalent positions in a distorted octahedron. A water molecule acts as the sixth ligand. One of the two CuHAPen complex ligands binds also a water molecule in the axial position. Temperature dependence of the magnetic susceptibility in the range 4.2-300 K showed that the ground state of the trinuclear cation is a spin doublet, with the quartet separated by -3 cm-I, and a second doublet at -90 cm-’. These data were interpreted with a strong ferromagnetic Cu-VO interaction and two weak coupling constants relative to the other Cu-VO and the CuCu interaction. The factors influencing the extent of ferromagnetic coupling between Cu and VO are discussed.