Optical response of the Cu 2 S 2 diamond core in (NGuaS) 2 Cl 2

Density functional theory (DFT) and time‐dependent DFT calculations are presented for the dicopper thiolate complex Cu 2 (NGuaS) 2 Cl 2 [NGuaS=2‐(1,1,3,3‐tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu 2 S 2 Cl 2 core and the spectroscopic response. This complex is relevant for the understanding of dicopper redox centers, for example, the Cu A center. Its UV/Vis absorption is theoretically studied and found to be similar to other structural Cu A 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 Cu 2 S 2 diamond core mediated between Cu 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 .