Copper(II) complexes of the fluoroquinolone antimicrobial ciproffoxacin. Synthesis, X-ray structural characterization, and potentiometric study

Reaction of the fluoroquinolone antimicrobial ciprofloxacin with copper(II) nitrate in the presence of 2,2'-bipyridine resulted in the isolation of the complex [Cu(cip)(bipy)(Cl)(0.7)(NO3)(0.3)] (NO3).2H(2)O. Reaction of an aqueous solution of ciprofloxacin.HCl and NaCl with CuCl2 at pH 5.0 resulted in the isolation of [Cu(cip)(2)]Cl-2.11H(2)O. The complex [Cu(cip)(bipy)(Cl)(0.7)(NO3)(0.3)] (NO3).2H(2)O crystallizes in the monoclinic space group P2(1)/n, with a = 13.955(8), b = 14.280(8), c = 14.192(6) Angstrom, beta = 93.10(4)degrees, Z = 4 with R = 0.046. The selective broadening of resonances in the C-13 NMR spectrum of ciprofloxacin by the addition of Cu2+(aq) was employed to probe metal ion binding sites in the ligand. The protonation constants of norfloxacin and ciprofloxacin, and the formation constants with copper(II), were determined by potentiometric titrations at 25 degrees C. The additions of ciprofloxacin to metal to form ML and ML(2) complexes exhibit stepwise formation constants of logK(1) 6.2(1) and log K-2 11.1(3), respectively.