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Synthesis, Structures, and Electrochemistry of Gold(III) Ethylenediamine Complexes and Interactions with Guanosine 5‘-Monophosphate

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posted on 2006-03-20, 00:00 authored by Shourong Zhu, Waldemar Gorski, Douglas R. Powell, Judith A. Walmsley
[Au(en)Cl2]Cl·2H2O, where en = ethylenediamine (1,2-diaminoethane), has been synthesized, and its structure has been solved for the first time by the single-crystal X-ray diffraction method. The complex has square-planar geometry about AuIII, and the anionic Cl- is located in the apical position and at a distance of 3.3033(10) Å compared to 2.2811(9) and 2.2836(11) Å for the coordinated Cl-. [Au(en)Cl2]Cl·2H2O belongs to the space group Pbca with a = 11.5610(15) Å, b = 12.6399(17) Å, c = 13.2156(17) Å, α = β = γ = 90°, and Z = 8. Bond lengths of Au−N are 2.03 Å. [Au(en)Cl2]Cl·2H2O is less thermally stable than [Au(en)2]Cl3 because of the replacement of two Cl ligands by a second en ligand in the latter. Cyclic voltammetry shows that the formal potential of AuIII/Au0 becomes more negative in the series [AuCl4]-, [Au(en)Cl2]+, and [Au(en)2]3+. 1H, 13C, and 31P NMR reveal that in an aqueous solution [Au(en)Cl2]+ bonds to guanosine 5‘-monophosphate, 5‘-GMP (1:1 mole ratio), via N(7), although the stability is not very high. NMR data also indicate that N(7)−O(6) or N(7)−phosphate 5‘-GMP chelation, as found in some gold(III) nucleotide complexes, is not present. The gold(III) complex undergoes hydrolysis at pH >2.5−3.0 and, therefore, N1 coordination to 5‘-GMP is not observed. No direct coordination between 5‘-GMP and [Au(en)2]Cl3 is observed.