title: Sulfur K-edge X-ray absorption spectroscopy and time-dependent density functional theory of arsenic dithiocarbamates.
abstract: S K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT) calculations were performed on a series of As[S2CNR2]3 complexes, where R2 = Et2, (CH2)5 and Ph2, to determine how dithiocarbamate substituents attached to N affect As[S2CNR2]3 electronic structure. Complimentary [PPh4][S2CNR2] salts were also studied to compare dithiocarbamate bonding in the absence of As. The XAS results indicate that changing the orientation of the alkyl substituents from trans to cis (R2 = Et2vs. (CH2)5) yields subtle variations whereas differences associated with a change from alkyl to aryl are much more pronounced. For example, despite the differences in As 4p mixing, the first features in the S K-edge XAS spectra of [PPh4][S2CNPh2] and As[S2CNPh2]3 were both shifted by 0.3 eV compared to their alkyl-substituted derivatives. DFT calculations revealed that the unique shift observed for [PPh4][S2CNPh2] is due to phenyl-induced splitting of the π* orbitals delocalized over N, C and S. A similar phenomenon accounts for the shift observed for As[S2CNPh2]3, but the presence of two unique S environments (As-S and As···S) prevented reliable analysis of As-S covalency from the XAS data. In the absence of experimental values, DFT calculations revealed a decrease in As-S orbital mixing in As[S2CNPh2]3 that stems from a redistribution of electron density to S atoms participating in weaker As···S interactions. Simulated spectra obtained from TDDFT calculations reproduce the experimental differences in the S K-edge XAS data, which suggests that the theory is accurately modeling the experimental differences in As-S orbital mixing. The results highlight how S K-edge XAS and DFT can be used cooperatively to understand the electronic structure of low symmetry coordination complexes containing S atoms in different chemical environments.
authors.affiliation: The George Washington University, Department of Chemistry, 725 21st St, NW, Washington, DC 20052, USA. srdaly@gwu.edu.
authors.forename: Courtney M
authors.initials: CM
authors.lastname: Donahue
authors.forename: Juan S Lezama
authors.initials: JS
authors.lastname: Pacheco
authors.forename: Jason M
authors.initials: JM
authors.lastname: Keith
authors.forename: Scott R
authors.initials: SR
authors.lastname: Daly
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D002219:Carbamates / Q000737:chemistry*; D003198:Computer Simulation; D004563:Electrochemistry; D004581:Electronics; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009991:Oscillometry; D011485:Protein Binding; D015203:Reproducibility of Results; D012492:Salts / Q000737:chemistry; D012984:Software; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014965:X-Rays
chemical_list: D002219:Carbamates; D012492:Salts; D013438:Sulfhydryl Compounds; D013455:Sulfur; D001151:Arsenic