Issue 4, 2015

Re-evaluating the Cu K pre-edge XAS transition in complexes with covalent metal–ligand interactions

Abstract

Three [Me2NN]Cu(η2-L2) complexes (Me2NN = HC[C(Me)NAr]2; L2 = PhNO (2), Image ID:c4sc03294b-t1.gif (3), PhCH[double bond, length as m-dash]CH2 (4); Ar = 2,6-Me2-C6H3; ArF = 3,5-(CF3)2-C6H3) have been studied by Cu K-edge X-ray absorption spectroscopy, as well as single- and multi-reference computational methods (DFT, TD-DFT, CASSCF, MRCI, and OVB). The study was extended to a range of both known and theoretical compounds bearing 2p-element donors as a means of deriving a consistent view of how the pre-edge transition energy responds in systems with significant ground state covalency. The ground state electronic structures of many of the compounds under investigation were found to be strongly influenced by correlation effects, resulting in ground state descriptions with majority contributions from a configuration comprised of a Cu(II) metal center anti-ferromagentically coupled to radical anion O2, PhNO, and Image ID:c4sc03294b-t2.gif ligands. In contrast, the styrene complex 4, which displays a Cu K pre-edge transition despite its formal d10 electron configuration, exhibits what can best be described as a Cu(I):(styrene)0 ground state with strong π-backbonding. The Cu K pre-edge features for these complexes increase in energy from 1 to 4, a trend that was tracked to the percent Cu(II)-character in the ground state. The unexpected shift to higher pre-edge transition energies with decreasing charge on copper (QCu) contributed to an assignment of the pre-edge features for these species as arising from metal-to-ligand charge transfer instead of the traditional Cu1s → Cu3d designation.

Graphical abstract: Re-evaluating the Cu K pre-edge XAS transition in complexes with covalent metal–ligand interactions

Supplementary files

Article information

Article type
Edge Article
Submitted
27 Oct 2014
Accepted
11 Feb 2015
First published
20 Feb 2015
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2015,6, 2474-2487

Re-evaluating the Cu K pre-edge XAS transition in complexes with covalent metal–ligand interactions

N. C. Tomson, K. D. Williams, X. Dai, S. Sproules, S. DeBeer, T. H. Warren and K. Wieghardt, Chem. Sci., 2015, 6, 2474 DOI: 10.1039/C4SC03294B

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