GOLD(III)-CYCLAM COMPLEXES - X-RAY CRYSTAL-STRUCTURE AND A USEFUL MACROCYCLIC EFFECT ON THE REDUCTION OF GOLD(III)

The X-ray crystal structure of the Au(III)-cyclam complex 1 shows a four-coordinate square-planar N4 geometry with the trans III conformation (or RRSS configuration) of cyclam and an average Au(III)-N bond distance of 2.04 angstrom. A block-diagonal-matrix least-squares refinement yielded a final R value of 0.069 for 2463 independent reflections. Crystals of 1.(NO3)1.5(ClO4)1.5.H2O (C10H26N5.5O11.5AuCl1.5) are triclinic, space group P1 with a = 15.148(8), b = 8.668(5), c = 8.267(5) angstrom, alpha = 109.17(6), beta = 101.08(5), gamma = 82.08(4) angstrom, V = 1003(1) angstrom3, d(calcd) = 2.177 g cm-3, and Z = 2. The reduction potential for Au(III) in 1 to Au0 varies with pH: -0.16 V vs SCE (pH 1.0) to -0.55 V (pH 9.0) at I = 0.50 (NaClO4) and 25-degrees-C, according to the degree of cyclam NH deprotonation. The macrocyclic gold(III) complex 1 has been found to possess very useful electrochemical properties for a novel gold-plating agent. The new properties of gold(III)-cyclam complexes have been characterized by the tetrafluorinated cyclam 7, tetramethylcyclam 8, and aminocyclam 9. Dissociation of two protons from the macrocyclic NH amines in 7 readily occurs with extremely low pK(a) values of 1.6 and 6.5 at 25-degrees-C and I = 0.10 (NaClO4). Cyclic and dc polarograms of 8 in DMF (25-degrees-C, I = 0.10; Et4NClO4) show the Au(III/II) quasi-reversible reduction wave at E1/2 = +0.18 V vs SCE.