Potentiometric and spectroscopic studies of transition-metal ions complexes with a quinolone derivative (cinoxacin). Crystal structures of new Cu(II) and Ni(II) cinoxacin complexes

Abstract

The interaction of cobalt(II), nickel(II), copper(II), and zinc(II) with Cinoxacin (HCx = 1-ethyl-1,4-dihydro-4-oxo(1,3)dioxolo(4,5-g)cinnoline-3-carboxylic acid), a 4-quinolone derivative, has been studied at metal/ligand ratios of 1:1-1:3 by means of pH-metric, spectrophotometric, and ESR methods. The formation constants have been determined and the stereochemistry for the metal ions in the species present in aqueous solutions (at 37 ± 0.1°C and I = 0.1 mol dm −3 NaCl) is discussed. In all the studied systems, complexes with different stoichiometric ratios, in which cinoxacin acts both as neutral and deprotonated ligand, are formed. The anomalous sequence of the stepwise stability constants observed for cobalt(II) and nickel(II) systems suggests changes in stereochemistry when CoCx 2 and NiCx 2 are formed. For zinc(II) this change has to be still more pronounced since a [ZnCx] + species has not been detected. For the Cu(II) system the sequence in the stepwise stability constants indicates the preferential formation of the [CuCx] + monocomplex. The crystal and molecular structure of new Cu(II) and Ni(II) complexes of cinoxacin have been investigated. The metal ion in [Cu(Cx) 2H 2O]·3H 2O is five-coordinated and the complex crystallizes in the triclinic P 1 space group with a = 10.620(1), b = 11.358(1), c = 12.440(2) A ̊ , α = 78.25(1), β = 80.24(1), γ = 63.34(1)°, and Z = 2 . The complex [Ni(Cx) 2-(DMSO) 2]·4H 2O contains six-coordinated Ni(II) and crystallizes in the triclinic P 1 space group with a = 8.866(3), b = 9.141(1), c = 11.580(1) A ̊ , α = 69.301(9), β = 82.17(2), γ = 75.86(2)°, and Z = 1 .