title: X-ray absorption spectroscopic and theoretical studies on (L)2[Cu2(S2)n]2+ complexes: disulfide versus disulfide(*1-) bonding.
abstract: Cu K-, Cu L-, and S K-edge X-ray absorption spectroscopic (XAS) data have been combined with density functional theory (DFT) calculations on [{(TMPA)Cu}2S2](ClO4)2 (1), [{Cu[HB(3,5-Pr(i)2pz)3]}2(S2)] (2), and [{(TMEDA)Cu}2(S2)2](OTf)2 (3) to obtain a quantitative description of their ground state wavefunctions. The Cu L-edge intensities give 63 and 37% Cu d-character in the ground state of 1 and 2, respectively, whereas the S K-pre-edge intensities reflect 20 and 48% S character in their ground states, respectively. These data indicate a more than 2-fold increase in the total disulfide bonding character in 2 relative to 1. The increase in the number of Cu-S bonds in 2 (mu-eta(2):eta(2) S2(2-) bridge) compared to 1 ((mu-eta(1):eta(1) S2(2-) bridge) dominantly determines the large increase in covalency and Cu-disulfide bond strength in 2. Cu K- and L- and S K-pre-edge energy positions directly demonstrate the Cu(II)/(S2(-))2 nature of 3. The two disulfide(*1-)'s in 3 undergo strong bonding interactions that destabilize the resultant filled antibonding pi* orbitals of the (S2(-))2 fragment relative to the Cu 3d levels. This leads to an inverted bonding scheme in 3 with dominantly ligand-based holes in its ground state, consistent with its description as a dicopper(II)-bis-disulfide(*1-) complex.
authors: Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors: Ritimukta
authors: R
authors: Sarangi
authors: John T
authors: JT
authors: York
authors: Matthew E
authors: ME
authors: Helton
authors: Kiyoshi
authors: K
authors: Fujisawa
authors: Kenneth D
authors: KD
authors: Karlin
authors: William B
authors: WB
authors: Tolman
authors: Keith O
authors: KO
authors: Hodgson
authors: Britt
authors: B
authors: Hedman
authors: Edward I
authors: EI
authors: Solomon
mesh_terms: D015502:Absorptiometry, Photon; D003300:Copper / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D004220:Disulfides; D009942:Organometallic Compounds; D003300:Copper