POTENTIOMETRIC AND SPECTROSCOPIC STUDIES OF TRANSITION-METAL IONS COMPLEXES WITH A QUINOLONE DERIVATIVE (CINOXACIN) - CRYSTAL-STRUCTURES OFNEW CU(II) AND NI(II) CINOXACIN COMPLEXES

The interaction of cobalt(II), nickel(II), copper(II), and zinc(II) wi th Cinoxacin (HCx = dro-4-oxo(1,3)dioxolo(4,5-g)cinnoline-3-carboxylic acid), a 4-quinolone derivative, has been studied at metal/ligand rat ios of 1:1-1:3 by means of pH-metric, spectrophotometric, and ESR meth ods. The formation constants have been determined and the stereochemis try for the metal ions in the species present in aqueous solutions (at 37 +/- 0.1 degrees C and I = 0.1 mol dm(-3) NaCl) is discussed. In al l 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 obs erved for cobalt(II) and nickel(II) systems suggests changes in stereo chemistry when CoCx(2) and NiCx(2) are formed. For zinc(II) this chang e has to be still more pronounced since a [ZnCx](+) species has not be en detected. For the Cn(II) system the sequence in the stepwise stabil ity constants indicates the preferential formation of the [CuCx](+) mo nocomplex. The crystal and molecular structure of new Cu(II) and Ni(II ) complexes of cinoxacin have been investigated The metal ion in [Cu(C x)(2)H2O]. 3H(2)O is five-coordinated and the complex crystallizes in the triclinic P (1) over bar space group with a = 10.620(1), b = 11.35 8(1), c = 12.440(2) Angstrom, alpha = 78.25(1), beta = 80.24(1), gamma = 63.34(1)degrees, and Z = 2. The complex [Ni(Cx)(2)-(DMSO)(2)]. 4H(2 )O contains six-coordinated Ni(II) and crystallizes in the triclinic P (1) over bar space group with a = 8.866(3), b = 9.141(1), c = 11.580( 1) Angstrom, alpha = 69.301(9), beta = 82.17(2), gamma = 75.86(2)degre es, and Z = 1. (C) 1997 Elsevier Science Inc.