Determination of Structure and Properties of Acetylacetone Dioxime,Benzoylacetone Dioxime and Bis-Benzoylacetone Dioximato-Copper (II): An Ultraviolet Study

UV spectra of acetylacetone dioxime (2,4-pentanedione dioxime = AADO), benzoylacetone dioxime (BADO) and bis-benzoylacetone dioximato-Cu(II) Cu- (BADO*)₂; BADO* = oxidized BADO] are recorded for aqueous and CHCl₃ solutions at different pH values and interpreted. pK_a values (1st dissociation constant) for AADO and BADO at constant ionic strenths (μ = 0.12) are derived: pK_a (AADO) = 10.50; pK_a (BADO) = 9.50, and the influence of molecular structure on acid-base properties is discussed. Diagrams of possible molecular orbital energy-level transitions for the oxime and the nitroso chromophores are given. The marked influence of acids (HC1) and bases (triethylamine, TEA) on the shape of the UV spectra of Cu- (BADO*)₂ is discussed and explained in terms of the acid-base properties of the nitroso and the oxime groups. Additional evidence has been adduced for the presence of nitroso group and of hydrogen bonds in these complexes.