Gold(III) complexes of amides of EDTA (L, L1) and PDTA (L2, L3) as model systems for gold(III)-peptide/protein interactions.: Synthesis of [AuLCl][AuCl4], [AuL2Cl]Cl and related complexes and the crystal and molecular structures of [Au(LH-1)Cl][AuCl4] containing a deprotonated amide ligand and of (LH2)2[AuCl4]3.5[AuCl2]0.5•2H2O

Reaction of 1,2-diaminoethane-N,N,N',N'-tetra-(N-methylacetamide), L, with K[AuCl4] in water gave the complex [AuLCl2][AuCl4] which when recrystallised from MeOH/H2O gave the amidate-containing complex [Au(LH-1)Cl][AuCl4] the crystal structure of which shows LH-1 to be present as a tridentate ligand coordinated via its amino group nitrogens and a deprotonated amide group. The geometry around the metal ion in both cation and anion is square planar with bond lengths, Au-N (amine) 2.06(1) and 2.105(9) Angstrom, Au-N (amidate) = 2.00(2) Angstrom, Au-Cl in the cation 2.274(3) and in the anion 2.262(4)-2.278(5) Angstrom. As very few crystal structures of gold(III)-peptide complexes have so far been reported this serves as a model compound for Au(III)-peptide/protein interactions. It is also the first reported structure of a Au(III) complex with tertiary amine donor groups. Reaction of [Au(LH-1)Cl][AuCl4] with dilute HCl in methanol-water gave the complex (LH2)(2)[AuCl4](3.5)[AuCl2](0.5).2H(2)O, the crystal structure of which confirms the presence of doubly protonated L cations and tetrachlorogold(III) and dichlorogold(I) anions. The synthesis of [(AuLCl2)-Cl-1][AuCl4].2H(2)O, [(AuLCl2)-Cl-2]Cl.H2O, [(AuLCl2)-Cl-3]Cl.CH3OH where L-1 is 1,2-diaminoethane-N,N,N',N'-tetra-acetamide, L-2 is 1,2-diaminopropane-N,N,N',N'-tetra-acetamide and L-3 is 1,2-diaminopropane-N,N,N',N'-tetra-(N-methylacetamide) are also reported. (C) 2003 Elsevier Science B.V. All rights reserved.