Crystal structure and solution chemistry of the cytotoxic complex 1,2-dichlolro(o-phenanthroline)gold(III) chloride

The crystal structure of the cytotoxic complex 1,2-dichloro(o-phenanthrolin e)gold(III) chloride ([AuphenCl(2)]Cl) has been solved through single cryst al X-ray diffraction methods. The complex is square planar and exhibits a q uite regular geometry. Crystals of the compound belong to the space group P 2(1)/n with a = 12.632(5), b = 16.916(3), c = 12.902(6) Angstrom, beta = 91 .31(3)degrees and Z = 8. The coordination of the two gold(III) ions in the asymmetric unit is completed by two chloride ions at 2.972(3) and 3.043(3) Angstrom, respectively, forming a distorted square pyramid. The behavior in solution of [AuphenCl(2)]Cl was further analyzed through H-1 NMR spectrosc opy. Results point out that the [Au(III)phen](3+) molecular fragment is sta ble in solution for several hours, even under physiological conditions, whe reas the two chloride ligands are released within approximately 30 min afte r dissolution in the buffer, at 25 degreesC. The gold(III) chromophore is e asily and quickly reduced by addition of stoichiometric amounts of sodium a scorbate; metallic gold is formed and free phenanthroline liberates. The im plications of these findings for the biological properties of the [Au(III)p hen](3+) species are discussed. (C) 2000 Elsevier Science B.V. All rights r eserved.