Optical response of the Cu₂S₂ diamond core in (NGuaS)₂Cl₂

Abstract

Density functional theory (DFT) and time-dependent DFT calculations are presented for the dicopper thiolate complex Cu2 (NGuaS)2 Cl2 [NGuaS=2-(1,1,3,3-tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu2 S2 Cl2 core and the spectroscopic response. This complex is relevant for the understanding of dicopper redox centers, for example, the CuA center. Its UV/Vis absorption is theoretically studied and found to be similar to other structural CuA models. The spectrum can be roughly divided in the known regions of metal d-d absorptions and metal to ligand charge transfer regions. Nevertheless the chloride ions play an important role as electron donors, with the thiolate groups as electron acceptors. The bonding mechanism is dissected by means of charge decomposition analysis which reveals the large covalency of the Cu2 S2 diamond core mediated between Cu dz2 and S-S π and π* orbitals forming Cu-S σ bonds. Measured resonant Raman spectra are shown for 360- and 720-nm excitation wavelength and interpreted using the calculated vibrational eigenmodes and frequencies. The calculations help to rationalize the varying resonant behavior at different optical excitations. Especially the phenylene rings are only resonant for 720 nm. © 2016 Wiley Periodicals, Inc.

[Cu6(NGuaS)6]2+ and its oxidized and reduced derivatives: Confining electrons on a torus

“…The bonding mechanisms are quite complex and at first glance one notices that the occupied frontier orbitals show no distinctive bonding character, but are of rather CuS antibonding character as found for the diamond core. For a detailed analysis of the involved mechanisms, we pursue the methodology used for the diamond core species . A first look at the Wiberg bond orders (WBOs) and total overlap populations (TOP), Table , shows that within one Cu 3 S 3 ring both CuS sites are of bonding nature.…”

“…To understand these differences, we performed a detailed CDA analysis. Contrary to the di‐copper core, where only one fragmentation is performed analyzing how the Cu ions interact with the NGuaS donors, we additionally performed a second CDA fragmentation. In this case the molecule is split into two Cu 3 (NGuaS) 3 fragments.…”

“…The possible impact of the solvent on the optical absorption spectra has already been discussed for the diamond core thiolate bridged copper complex. There the solvent gives rise to an energy level shifting as well as the removal of accidental degeneracy . Hence, we do not want to discuss the influence of the solvent in detail, but rather immediately show the calculated spectra in the implicit solvent, Figure .…”

“…For the CDA, we split the molecule into two fragments and analyze how the mole‐cular orbitals (MOs) are composed of the fragmental orbitals (FOs). To interpret the bonding character, the overlap S and the (total) overlap population (T)OP are calculated, as done for the dinuclear species …”

“…In the bioinorganic context, Henkel and coworkers synthesized the structurally inspired Cu A model complex Cu(II) 2 (NGuaS) 2 Cl 2 (with NGuaS = o‐SC 6 H 4 NC(NMe 2 ) 2 ) . The complex has been theoretically studied in detail with respect to the broken symmetry (BS) minimum energy wave function, its bonding mechanism and the spectroscopic features . It is known that nitrogen bases, guanidine ligands in special, serve as good donors in metal bonding .…”