Synthesis, spectroscopy, electrochemistry, and molecular structure of tetrakis{(E)-2-((pyridin-2-ylimino)methyl)phenolato}(hydroxido)0.5(nitrato)1.5-tetracopper(II) nitrate hydroxide

Abstract

Reaction between (E)-2-((pyridin-2-ylimino)methyl)phenol (HL) and copper(II) nitrate provides tetrakis{(E)-2-((pyridin-2-ylimino)methyl)phenolato}(hydroxido)0.5(nitrato)1.5-tetracopper(II) nitrate hydroxide, [(CuL)4(NO3)1.5(OH)0.5](NO3)(OH) (1). ESI-mass spectra show the ion peaks for the dinuclear species at m/z 565 for [(CuL)2(HCO2)]+ and 521 for [(CuL)2+H]+ and the mononuclear species at m/z 260 for [(CuL)]+. Vibrational spectra show very strong bands at 1604/1546 cm−1 for ν(C = N/C = C) and at 1384, 1351 cm−1 for ν(NO3–). Cyclic voltammograms demonstrate an irreversible redox processes for the Cu(II)/Cu(I) and Cu(I)/Cu(0) couples in acetonitrile. X-ray molecular structure determination explores the formation of a cationic tetranuclear copper(II)-complex, in which a deprotonated ligand molecule chelates to one copper ion with the phenolate-O and imino-N atoms. In addition, a phenolate-O atom bridges between two neighboring copper ions and a pyridine-N atom coordinates to a third copper ion, so that each ligand bridges among three copper ions in a κ2N,O:κO:κN' coordination sphere. Thus, the four copper ions and four chelating-bridging ligands assemble primarily into a cationic [(CuL)4]4+ complex. The two copper ions are further coordinated by either a nitrate anion (75% occupancy) or a hydroxide anion (25% occupancy) and form the core of a tetranuclear [(CuL)4(NO3)1.5(OH)0.5]2+ cation.