Magnetism in Thiolated Gold Model Junctions

Three stable, neutral diradical model molecules with an even number of electrons, based on pairs of small thiolated Au clusters connected via Au–Au bonding, are studied within a broken symmetry unrestricted density functional theory involving a set of exchange-correlation functionals, including PBE, M06L, TPSS, B3LYP, M06, and TPSSh. The models, mostly with an antiferromagnetic ground state within the theory used, are analyzed in terms of the vertical spin–flip energy splitting, total spin expectation values, Heisenberg exchange coupling constant, magnetic orbitals and their overlap, diradical character, binding energies, natural bond-order analysis, and bond index of the central Au–Au bond. The spin-symmetry breaking is attributed to the open-shell nature of the dimerized monomer constituents and the structural feature of the facing S–Au–S edges, in combination with the attractive unsupported metallophilic d–d interaction of the incident Au atoms, allowing a weak coupling of the spins localized sideways. The modeling provides insight to AuI–AuI interactions, potentially useful in design of novel gold-based magnetic nanoscopic assemblies.