Effect of gold atom contact in conjugated system of one dimensional octane dithiolate based molecular wire: A theoretical charge density study

To understand the effect of Au and thiol atoms in octane molecule, a structural and charge density analysis has been carried out by high level ab initio quantum chemical calculations using MP2 and B3PW91 methods with the basis sets 6-311G(d,p) and LANL2DZ. The optimized geometries, specifically, the geometry obtained from both levels reveal the effect of S- and Au-atoms in octane molecule. An introduction of sulfur atom in octane molecule lengthen its backbone C-C bond distances, and further adding of Au-atom at the terminals of octane dithiolate stabilizes these distances. The bond densities of the C-C bonds of octane are ∼1.6 eÅ−3, these values are decreased significantly and the charges are largely depleted, when thiol and Au-atoms added in the octane molecule. The presence of negative Laplacian ∇2ρ(r) at bond critical points of C-C and C-H bonds, indicate, the charges are concentrated in these bonds, confirm that these bonds exhibit an open shell type interaction. The moderate values of density and the negative Laplacian of S-C bonds confirm the covalent character. The positive ∇2ρ(r) value of Au-S bonds, characterize, the bonding interaction is a closed shell interaction. The combined observed low value of electron density and the positive Laplacian of Au-S bond comprises, the gold and S interaction is not a covalent interaction, but it is a very weak coordination bond interaction. The small positive value of total energy density in Au-S bond indicates, the charges in these bonds are highly depleted and this is further confirmed by the Laplacian of bond characterization.