Solvation and catalyst–substrate superstructure of a tungsten tris(dithiolene) complex dissolved in water–acetone A molecular dynamics model calculation

Abstract

The intermolecular interactions of the catalyst tris(1,2-ethylenedithiolate-S,S′)tungsten, W(S₂C₂H₂)₃, with the molecules of a 25:75 water–acetone mixed solvent, are examined by statistical mechanical methods, and specifically by a molecular dynamics (MD) technique, using charge distributions obtained by extended Hückel calculations. The results are presented in the form of pair correlation functions (PCF), and show that an average of up to three water molecules come close to the sites of the catalyst, whereas the acetone molecules form an open cage at a somewhat longer distance. The supramolecular structure around the catalyst is asymmetric, and is examined in the two characteristic geometries corresponding to the D_3h and C_2v symmetries which the ‘tris(dithiolene)’ molecule transiently assumes during its fluxional metamorphoses in solution. At large distance (large values of the correlation parameter r) the system is homogeneous. Yet, at nanometer distances the symmetry breaks down, and the system becomes highly asymmetric with differentiation (selectivity) in space. The mobility of the water and acetone molecules, close to the catalyst, was also studied by estimating the translational self-diffusion coefficients D_wat and D_acet from the center of mass linear velocity correlation functions. The results show that the water molecules are more mobile than the acetone molecules, which is the opposite of what happens without the catalyst.