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Hoffmann, Alexander; Stanek, Julia; Dicke, Benjamin; Peters, Laurens; Grimm-Lebsanft, Benjamin; Wetzel, Alina; Jesser, Anton; Bauer, Matthias; Gnida, Manuel; Meyer-Klaucke, Wolfram; Rübhausen, Michael; Herres-Pawlis, Sonja (2016): Implications of Guanidine Substitution on Copper Complexes as Entatic-State Models. In: European Journal of inorganic Chemistry, No. 29: pp. 4731-4743
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The guanidine-quinoline ligand dimethylethylene-guanidinoquinoline (DMEGqu) is able to stabilise bis(chelate)copper complexes in an intermediate geometry between tetrahedral and square-planar environments. The structures of the obtained complexes model the entatic state and have been investigated in solid state by single-crystal X-ray diffraction and in the solid state and in solution by X-ray absorption spectroscopy. The dimethylethyleneguanidine (DMEG) unit of the DMEGqu ligand displays a smaller steric encumbrance than the tetramethylguanidine (TMG) counterpart;this allows slightly larger structural changes upon oxidation than those for the TMG counterparts. Moreover, triflate coordination was possible for the Cu-II DMEG complexes. DFT analyses revealed that good structural and optical descriptions are possible through the use of the hybrid functionals B3LYP and TPSSh in combination with the triple-zeta basis set def2-TZVP and the inclusion of empirical dispersion with Becke-Johnson damping and a suitable solvent model. The orbital analysis gives insights into the electronic structure of the complexes and their charge-transfer behaviour.