title: Using solution- and solid-state S K-edge X-ray absorption spectroscopy with density functional theory to evaluate M-S bonding for MS4(2-) (M = Cr, Mo, W) dianions.
abstract: Herein, we have evaluated relative changes in M-S electronic structure and orbital mixing in Group 6 MS4(2-) dianions using solid- and solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well as density functional theory (DFT; M = Cr, Mo, W) and time-dependent density functional theory (TDDFT) calculations. To facilitate comparison with solution measurements (conducted in acetonitrile), theoretical models included gas-phase calculations as well as those that incorporated an acetonitrile dielectric, the latter of which provided better agreement with experiment. Two pre-edge features arising from S 1s → e* and t electron excitations were observed in the S K-edge XAS spectra and were reasonably assigned as (1)A1 → (1)T2 transitions. For MoS4(2-), both solution-phase pre-edge peak intensities were consistent with results from the solid-state spectra. For WS4(2-), solution- and solid-state pre-edge peak intensities for transitions involving e* were equivalent, while transitions involving the t orbitals were less intense in solution. Experimental and computational results have been presented in comparison to recent analyses of MO4(2-) dianions, which allowed M-S and M-O orbital mixing to be evaluated as the principle quantum number (n) for the metal valence d orbitals increased (3d, 4d, 5d). Overall, the M-E (E = O, S) analyses revealed distinct trends in orbital mixing. For example, as the Group 6 triad was descended, e* (π*) orbital mixing remained constant in the M-S bonds, but increased appreciably for M-O interactions. For the t orbitals (σ* + π*), mixing decreased slightly for M-S bonding and increased only slightly for the M-O interactions. These results suggested that the metal and ligand valence orbital energies and radial extensions delicately influenced the orbital compositions for isoelectronic ME4(2-) (E = O, S) dianions.
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. erb@lanl.gov stosh@lanl.gov.
authors.forename: Angela C
authors.initials: AC
authors.lastname: Olson
authors.forename: Jason M
authors.initials: JM
authors.lastname: Keith
authors.forename: Enrique R
authors.initials: ER
authors.lastname: Batista
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Boland
authors.forename: Scott R
authors.initials: SR
authors.lastname: Daly
authors.forename: Stosh A
authors.initials: SA
authors.lastname: Kozimor
authors.forename: Molly M
authors.initials: MM
authors.lastname: MacInnes
authors.forename: Richard L
authors.initials: RL
authors.lastname: Martin
authors.forename: Brian L
authors.initials: BL
authors.lastname: Scott
mesh_terms: D000838:Anions / Q000737:chemistry; D002857:Chromium / Q000737:chemistry*; D008982:Molybdenum / Q000737:chemistry*; D011789:Quantum Theory; D012996:Solutions / Q000737:chemistry; D014414:Tungsten / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D000838:Anions; D012996:Solutions; D002857:Chromium; D008982:Molybdenum; D014414:Tungsten