DICOPPER COMPLEXES WITH A DISSYMMETRIC DICOMPARTMENTAL SCHIFF BASE-OXIME LIGAND - SYNTHESIS, STRUCTURE, AND MAGNETIC-INTERACTIONS

A dicopper(II) complex with an unsymmetrical dicompartmental ligand co ntaining bridging phenolic oxygen atoms was synthesized by stepwise co ndensation, in the presence of copper(II) ions, of 2,6-diformyl-4-meth ylphenol and diaminopropane, followed by hydroxylamine. The complex wa s isolated and characterized as Cl-, [Cu2Cl4](2-), and ClO4- derivativ es. A byproduct of the reaction, a copper(II) complex with a substitut ed salycilaldoxime, was also structurally characterized. The structure of the binuclear cation of major interest is nearly planar, with the copper(II) ions slightly displaced to opposite sides of the plane of t he donor atoms (<0.20 Angstrom). [Cu2Cl4](2-) is an unusual anion, hav ing been characterized previously in only five other compounds. It is flat, with both copper(I) ions in trigonal planar environments and two chlorides bridging the two copper(I) centers. X-ray structure determi nations of the [Cu2Cl4](2-) and ClO4- derivatives of the dicopper comp lex reveal a strong tendency for the formation of coordination dimers and tetramers. These aggregates arise because an oxime oxygen from one binuclear cationic complex coordinates axially to the copper atom of another such complex. In the case of the [CU2Cl4](2-) salt, the anion forms additional bridges between binuclear complexes,resulting in poly meric chains. In the ClO4- salt, however, aggregation is limited to th e tetramer because of terminal axially coordinated methanol molecules. Temperature-dependent magnetic susceptibility measurements show stron g antiferromagnetic interaction (ca. -700 cm(-1)) between the two copp er(II) ions within one binuclear cationic complex. No magnetic interac tions have been observed between binuclear units. Cyclic voltammograms were measured in dimethylformamide (DMF) solution and show two separa te reduction waves at -1.47 and -1.04 V, as well as an oxidation wave at +0.04V (vs Fc(+)/Fc). The mixed-valent Cu-II/Cu-I complex is thermo dynamically stable toward disproportionation.