The computational study of 'model' pollutants in clay montmorillonite

The adsorption of Ru(NH{dollar}sb3)sb6sp{lcub}3+{rcub},{dollar} Co(sep){dollar}sp{lcub}3+{rcub}{dollar} (sep = C{dollar}rmsb{lcub}12{rcub}Hsb{lcub}30{rcub}Nsb8),{dollar} Co(en){dollar}sb3sp{lcub}3+{rcub}{dollar} (en = C{dollar}rmsb2Hsb8Nsb2),{dollar} and Co(bpy){dollar}sb3sp{lcub}3+{rcub}{dollar} (bpy = 2,2{dollar}spprime{dollar}-bipyridine) in clay montmorillonite was studied using UV spectroscopy and electrochemistry. The observed potential shift between divalent and trivalent species at clay-modified electrode (CME) was correlated with the calculated adsorption energy difference from lattice minimizations. CME was also used to monitor the diffusion of the metal complexes through the clay over time. Molecular dynamics simulation based on atomistic modeling was performed to compare with these experimental observations. The calculated rate of diffusion measured by mean squared displacement (MSD) was consistent with the observations monitored by CME. The same study was repeated for the divalent cobalt trisbipyridal complexes, Co(bpm){dollar}sb3sp{lcub}2+{rcub}{dollar} (bpm = 2,2{dollar}spprime{dollar}-bipyrimidine), Co(bpy){dollar}sb3sp{lcub}2+{rcub},{dollar} and Co(bpz){dollar}sb3sp{lcub}2+{rcub}{dollar} (bpz = 2,2{dollar}spprime{dollar}-bipyrazine). Relative order of calculated diffusion rate by MSD analysis of these cobalt complexes in clay interlayer region was again consistent with the experimental results. These cobalt tris-ligand complexes were also studied for the quantum mechanical electronic structure calculations. The previously observed divalent ruthenium trisbipyridine complex was used for the computation to make sure if our computational approach is valid. The trends in calculated LUMO energies were consistent with the trends in electrochemical reduction potential of ruthenium trisbipyridine complex. Trends in calculated electronic transition energies for the metal-to-ligand charge transfer (MLCT) were also consistent with the trends for observed spectroscopic results. Cobalt trisbipyridal complexes were studied for comparison of calculated LUMOs and reduction potentials. Good correlation was obtained for trends with these cobalt tris-ligand complexes. The previously proposed mechanism of electrochemical cleavage of phenylsulfones was elucidated by quantum mechanical electronic structure calculations. The results from the Hartree-Fock calculations were consistent with the proposed mechanism of two electron reduction scheme. The molecular orbital surface and spin density was used to interpret the possible site of electron transfer. The calculated Mulliken and Lowdin bond orders were also consistent with the possible location of reduction of 6-substituted PSTHPs (5-phenylsulfonyl-3,4,5,6-tetrahydropyran-2-one). Overall, the computational technique based on atomistic modeling with molecular dynamics simulation as well as quantum mechanical Hartree-Fock calculations produced good consistency with trends in electrochemical and spectroscopic observations.