Catching an Entatic State—A Pair of Copper Complexes


  • We thank the Deutsche Forschungsgemeinschaft (DFG FOR 1405), the Fonds der Chemischen Industrie (FCI for S. H.-P.), the Evonik-Stiftung (R.H.), and the Bundesministerium für Bildung und Forschung (BMBF 05K12GU1 for A.W. and MoSGrid initiative 01IG09006) for financial support, the beamline staff at the Deutsches Elektronen-Synchrotron (DESY Photon Science (Germany)) and the Diamond Light Source (UK) for assistance with XAS data collection, P. Höfer at the MPI Mülheim for square-wave voltammetric measurements, and the Paderborn Cluster for Parallel Computing (PC2 Paderborn) and the Center for Information Services and High Performance Computing of the Technische Universität Dresden for calculation time.


The structures of two types of guanidine–quinoline copper complexes have been investigated by single-crystal X-ray crystallography, K-edge X-ray absorption spectroscopy (XAS), resonance Raman and UV/Vis spectroscopy, cyclic voltammetry, and density functional theory (DFT). Independent of the oxidation state, the two structures, which are virtually identical for solids and complexes in solution, resemble each other strongly and are connected by a reversible electron transfer at 0.33 V. By resonant excitation of the two entatic copper complexes, the transition state of the electron transfer is accessible through vibrational modes, which are coupled to metal–ligand charge transfer (MLCT) and ligand–metal charge transfer (LMCT) states.