Structure and bonding of gold(I) and gold(III) nucleosides studied by 197Au Mössbauer spectroscopy

Abstract

197Au Mössbauer spectra of the series of complexes of gold(I), Au(nucl) 2Cl and gold(III), Au(nucl)Cl 3, Au(nucl - H +)Cl 2 and Au(nucl) 2Cl 3 were measured at 4.2 K, (nucl = nucleoside, e.g. guanosine(guo), inosine(ino), triacetylguanosine-(trguo) and triacetylinosine(trino)). It is concluded from the spectra that the gold(I) nucleosides have linear ClAuN coordination, with one coordinated nucleoside molecule per gold(I) ion, bound via the N(7) atom. The σ-donor strength of the guo ligand is somewhat higher than that of the ino ligand. The complexes Au(ino)Cl 3 and Au(guo)Cl 3, in the series Au(nucl)Cl 3, have significantly higher IS and QS values than the corresponding complexes with the triacetylnucleosides, Au(trino)Cl 3 and Au(trguo)Cl 3. This may be explained by a weak O(6)-interaction with gold(III), in a nearly trigonal bipyramidal configuration in the former case and by the presence of the strongly electron withdrawing acetyl groups in the latter, which reduces the donor strength of their N(7) atoms. The complexes of the Au(nucl - H +)Cl 2 series all appear to have a polymeric structure. The gold(III) ion is bound to the N(7) atom and the O(6) or the N(1) atom of the nucleosides. Finally, the Mössbauer spectra of the series Au(nucl) 2)Cl 3 can only be explained by assuming approximately octahedral AuN 2Cl 4 structures, with bridging chlorine atoms.