Den entatischen Zustand im Griff – ein Duo von Kupfer‐Komplexen

Abstract

Die Struktur von zwei Typen von Guanidin-Chinolin-Kupfer-Komplexen wurde mittels Einkristallrçntgen-strukturanalyse, K-Kanten-Rçntgenabsorptionsspektroskopie (XAS), Resonanz-Raman-und UV/Vis-Spektroskopie, Cyclovoltammetrie und Dichtefunktionaltheorie (DFT) untersucht. Unabhängig vom Oxidationszustand weisen beide Strukturen sowohl im Festkçrper als auch in Lçsung nahezu die gleiche Struktur auf und kçnnen durch einen reversiblen Elektronentransfer bei 0.33 V ineinander überführt werden. Durch eine resonante Anregung der beiden entatischen Kupferkomplexe kann der Übergangszustand des Elektronentransfers über die Schwingungsmoden, die entweder den Metall-Ligand-ChargeTransfer-Zustand (MLCT) oder den Ligand-Metall-ChargeTransfer-Zustand (LMCT) verbinden, untersucht werden.

Geometrical and optical benchmarking of copper(II) guanidine–quinoline complexes: Insights from TD‐DFT and many‐body perturbation theory (part II)

“…With the hybrid guanidine–quinoline ligand TMGqu molecular structures of the Cu(II) complexes [Cu(TMGqu) 2 ][TfO] 2 and [Cu(TMGqu) 2 ][PF 6 ] 2 have been obtained experimentally from crystal structures . The correct description of the donor competition can be rather challenging, such that we focus on the interplay of guanidine and quinoline units.…”

“…The correct description of the donor competition can be rather challenging, such that we focus on the interplay of guanidine and quinoline units. The quinoline is in general a softer donor, whereas the guanidine is slightly harder but being able to coordinate copper in all oxidation states . Moreover, the guanidine unit is sterically very encumbering.…”

“… For the regarded cation, two experimental structures are known . The crystallographic mean deviation adds to the extreme values of the two structures.…”

“…Since the postulate of the “entatic state” by Vallee and Williams in 1968, low molecular weight Cu(II/I) systems have been investigated to model the coordination geometry and the electron transfer properties of enzymatic systems like the type 1 copper sites in blue copper proteins. And although more recent studies have challenged the concept of the “entatic state” as protein matrix derived distortion of the active site in favor of an electronic interpretation, the understanding of the influence of coordination geometry on electron transfer is still vital for inorganic and biochemical chemistry alike …”

“…Copper‐based guanidine complexes find application not only as biomimetic models for activation of dioxygen but also as polymerisation catalysts . In recent work from our group, a resonance Raman study on a pair of Cu(I) and Cu(II) guanidine–quinoline bis(chelate) complexes with highly interesting charge‐transfer properties was performed to optically access the “entatic state,” the intermediate state of inner‐sphere electron transfer. In a previous publication, we provided with an extensive theoretical study on the Cu(I) complex from this pair, which consisted of structural and optical benchmarking, as well as conformational and isomer analysis at density functional theory (DFT) level of theory, with an emphasis on the amount of exact exchange used.…”