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Liang HC, Henson MJ, Hatcher LQ, Vance MA, Zhang CX, Lahti D, Kaderli S, Sommer RD, Rheingold AL, Zuberbuhler AD, Solomon EI, Karlin KD: Solvent effects on the conversion of dicopper (II) micro-eta (2):eta (2)-peroxo to bis-micro-oxo dicopper (III) complexes: direct probing of the solvent interaction. Inorg Chem. 2004 Jul 12;43(14):4115-7.
A new tridentate ligand, PYAN, is employed to investigate solvent influences for dioxygen reactivity with [Cu (PYAN)(MeCN)] B (C (6) F (5))(4) (1). Stopped-flow kinetic studies confirm that the adducts [[u (II)(PYAN)] 2)(O (2))][B (C (6) F (5))(4)](2) (2 (Peroxo)) and [[u (III)(PYAN)] 2)(O)(2)][B (C (6) F (5))(4)](2) (2 (Oxo)) are in rapid equilibrium. Thermodynamic parameters for the equilibrium between 2 (Peroxo) and 2 (Oxo) re as follows: THF, deltaH degrees approximately -15.7 kJ/mol, deltaS degrees approximately -83 J/K.mol; acetone, deltaH degrees approximately -15.8 kJ/mol, deltaS degrees approximately -76 J/K.mol. UV-visible absorption and resonance Raman spectroscopic signatures demonstrate that the equilibrium is highly solvent dependent; the mixture is mostly 2 (Peroxo) in CH (2) Cl (2), but there are significantly increasing quantities of 2 (Oxo) along the series methylene chloride --> diethyl ether --> acetone --> tetrahydrofuran (THF). Copper (II)-N (eq) stretches (239, 243, 244, and 246 cm (-)(1) in CH (2) Cl (2), Et (2) O, acetone, and THF, respectively) are identified for 2 (Peroxo), but they are not seen in 2 (Oxo), revealing for the first time direct evidence for solvent coordination in the more open 2 (Peroxo) structure. |
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