Prediction of nonradical Au(0)-containing precursors in nanoparticle growth processes.

This density functional theory (DFT) investigation examines the formation of nonradical Au(0) species from the reduction of Au(I) species. The Au(I) complexes of interest are AuCl2(-), AuBr2(-), AuI2(-), AuClPH3, and AuCl(H)SCH3(-), which are precursors for gold nanoparticle and cluster formation. Reaction of two of the Au(I) species with a hydride results in ejection of two of the ligands and formation of Au2 with two ligands still attached. AuX2(-) (where X = Cl, Br, or I) reactions eject two halides and form Au2X2(2-). AuClL(-) (where L = PH3, HSCH3, or SCH3(-)) reactions can eject either chloride, HCl, PH3, HSCH3, or SCH3(-) and form Au(0)L2(q-) or Au(0)ClL(q-) (q = 0, 1, 2). The Au2Cl2(2-) complex can further react with AuCl2(-), which forms Au3Cl3(2-) and a chloride anion. The new Au3Cl3(2-) species can then react with AuCl2(-) or Au2Cl2(2-) or with another Au3Cl3(2-). Larger clusters can be formed from these precursors. In this work, reactions in both methanol and benzene solvents are considered as models for one-phase and two-phase gold nanoparticle growth processes. Overall, this investigation shows how Au(0)-containing species can be formed without assuming the formation of Au(0) atoms (radical species).