New powerful reagents based on dihalogen/N,N′-dimethylperhydrodiazepine-2,3-dithione adducts for gold dissolution:: the IBr case

The synthesis, X-ray structure [monoclinic, P2(1)/n, a=12.1690(1),b=7.8360(1), c=14.4250(1) Angstrom, beta=113.808(2)degrees], spectroscopic and electrochemical characterization of a new powerful reagent based on the iodine monobromide adduct of the N,N'-dimethylperhydrodiazepine-2,3-dithione (Me(2)dazdt) ligand, able to oxidize gold metal in a one-step reaction under mild conditions, is reported. The gold metal dissolution has been performed on gold powder, wires and Au/Ti thin layers. The oxidation product has been isolated and structurally characterised as [Au(Me(2)dazdt)Br-2]IBr2 [monoclinic, C2/c, a=26.523(8), b=10.191(6), c=14.549(7) Angstrom, beta=111.57(2)degrees]. The metal is essentially within a square planar geometry, Me(2)dazdt acts as an S,S chelating ligand and two bromide ligands complete the geometry around the metal. The IBr2- counteranion is essentially linear and shows I-Br bond lengths slightly asymmetric [Br(4)-I(1) 2.742(3), Br(3)-I(1) 2.682(2) Angstrom]. A comparison with the gold removal from Si/SiO2/Au/Ti thin layers of comparable thickness to that found in microelectronic devices, by using THF solutions of IBr and I-2 adducts of the Me(2)dazdt donor, as well as the currently used I-2/I- aqueous solutions, shows that these dihalogens-adducts produce a quantitative gold removal in shorter times and leaving the underlying layer perfectly clean, and are thus highly desirable as new etching agents in the gold-based technology of semiconductor devices.