Monocationic gold(III) Gly-L-His and L-Ala-L-His dipeptide complexes: crystal structures arising from solvent free and solvent-containing crystal formation and structural modifications tuned by counter-anions.

Monocationic gold(III) complexes with histidine-containing peptides, glycyl-L-histidine (Gly-L-His) and L-alanyl-L-histidine (L-Ala-L-His) have been synthesized and characterized by (1)H NMR spectroscopy and X-ray crystallography. The crystallized Au(III) complexes, [Au(Gly-L-His-N,N',N'')Cl]NO(3)·1.25H(2)O and [Au(L-Ala-L-His-N,N',N'')Cl]NO(3)·2.5H(2)O, were obtained from water solution at pH < 1.0. The chemical shifts in the (1)H NMR spectra of [Au(Gly-L-His-N,N',N'')Cl]NO(3)·1.25H(2)O and [Au(L-Ala-L-His-N,N',N'')Cl]NO(3)·2.5H(2)O complexes were compared with those for the corresponding Pd(II) complexes and for Pd(II) and Au(III) complexes with Gly-Gly-L-His tripeptide. Crystal data for the hydrated [Au(Gly-L-His-N,N',N'')Cl]NO(3)·1.25H(2)O complex and its serendipitously obtained unhydrated form were compared with previously reported X-ray data for the hydrated chloride complex [Au(Gly-L-His-N,N',N'')Cl]Cl·3H(2)O and with the analogous, though uncharged, Pd(II) and Pt(II) complexes. Furthermore, in the present study the crystal structure of the nitrate salt of Au(III) complex with L-Ala-L-His dipeptide, [Au(L-Ala-L-His-N,N',N'')Cl]NO(3)·2.5H(2)O has been determined.