(E)-2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione: Tautomery and coordination to copper(II)

(E)-2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione (H2L) was synthesized by azocoupling of diazonium salt of 2-hydroxyaniline with 1-phenylbutane-1,3-dione and characterized by IR, H-1 and C-13 NMR spectroscopies and X-ray diffraction analysis. In solution, H2L exists as a mixture of the enol-azo and hydrazone tautomeric forms and a decrease of temperature and of solvent polarity shifts the tautomeric balance to the hydrazone form. In the solid state, H2L crystallizes from ethanol-water in the monohydrate hydrazone form, as shown by X-ray analysis. The dissociation constants of H2L (pK(1) = 5.98 +/- 0.04, pK(2) = 9.72 +/- 0.03) and the stability constants of its copper(II) complex (log beta(1) = 11.01 +/- 0.07, log beta(2) = 20.19 +/- 0.08) were determined by the potentiometric method in aqueous-ethanol solution. The copper(II) complex [Cu-2(mu-L)(2)](n) was isolated in the solid state and found by X-rays to be a coordination polymer of a binuclear core with a distorted square pyramidal metal coordination geometry. (C) 2011 Elsevier B.V. All rights reserved.