title: Sulfur K-edge X-ray absorption spectroscopy as a probe of ligand-metal bond covalency: metal vs ligand oxidation in copper and nickel dithiolene complexes.
abstract: A combination of Cu L-edge and S K-edge X-ray absorption data and density functional theory (DFT) calculations has been correlated with 33S electron paramagnetic resonance superhyperfine results to obtain the dipole integral (Is) for the S 1s-->3p transition for the dithiolene ligand maleonitriledithiolate (MNT) in (TBA)2[Cu(MNT)2] (TBA= tetra-n-butylammonium). The results have been combined with the Is of sulfide derived from XPS studies to experimentally obtain a relation between the S 1s-->4p transition energy (which reflects the charge on the S atom, QSmol) and the dipole integral over a large range of QSmol. The results show that, for high charges on S, Is can vary from the previously reported Is values, calculated using data over a limited range of QSmol. A combination of S K-edge and Cu K- and L-edge X-ray absorption data and DFT calculations has been used to investigate the one-electron oxidation of [Cu(MNT)2]2- and [Ni(MNT)2]2-. The conversion of [Cu(MNT)2]2- to [Cu(MNT)2]- results in a large change in the charge on the Cu atom in the molecule (QCumol) and is consistent with a metal-based oxidation. This is accompanied by extensive charge donation from the ligands to compensate the high charge on the Cu in [Cu(MNT)2]- based on the increased S K-edge and decreased Cu L-edge intensity, respectively. In contrast, the oxidation of [Ni(MNT)2]2- to [Ni(MNT)2]- results in a small change in QNimol, indicating a ligand-based oxidation consistent with oxidation of a molecular orbital, psiSOMO (singly occupied molecular orbital), with predominant ligand character.
authors.affiliation: Department of Chemistry, Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309, USA.
authors.forename: Ritimukta
authors.initials: R
authors.lastname: Sarangi
authors.forename: Serena
authors.initials: S
authors.lastname: DeBeer George
authors.forename: Deanne Jackson
authors.initials: DJ
authors.lastname: Rudd
authors.forename: Robert K
authors.initials: RK
authors.lastname: Szilagyi
authors.forename: Xavi
authors.initials: X
authors.lastname: Ribas
authors.forename: Concepció
authors.initials: C
authors.lastname: Rovira
authors.forename: Manuel
authors.initials: M
authors.lastname: Almeida
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D003300:Copper / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D014732:Vibration; D014965:X-Rays
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; D013455:Sulfur; D003300:Copper; D009532:Nickel