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

Abstract

The synthesis, X-ray structure [monoclinic, P2₁/n, a = 12.1690(1), b = 7.8360(1), c = 14.4250(1) Å, β = 113.808(2)°], spectroscopic and electrochemical characterization of a new powerful reagent based on the iodine monobromide adduct of the N,N′-dimethylperhydrodiazepine-2,3-dithione (Me₂dazdt) 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(Me₂dazdt)Br₂]IBr₂ [monoclinic, C2/c, a = 26.523(8), b = 10.191(6), c = 14.549(7) Å, β = 111.57(2)°]. The metal is essentially within a square planar geometry, Me₂dazdt 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) Å]. 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 I₂ adducts of the Me₂dazdt donor, as well as the currently used I₂/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.