X-ray absorption edge spectroscopy and computational studies on LCuO 2 species: Superoxide-CuII versus peroxide-Cu III bonding

Ritimukta Sarangi, Nermeen Aboelella, Kiyoshi Fujisawa, William B Tolman, Britt Hedman, Keith O. Hodgson, Edward I. Solomon

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Abstract

The geometric and electronic structures of two mononuclear CuO2 complexes, [Cu(O2){HB(3-Ad-5-iPrpz)3}] (1) and [Cu(O2)(β-diketiminate)] (2), have been evaluated using Cu K- and L-edge X-ray absorption spectroscopy (XAS) studies in combination with valence bond configuration interaction (VBCI) simulations and spin-unrestricted broken symmetry density functional theory (DFT) calculations. Cu K- and L-edge XAS data indicate the Cu(II) and Cu(III) nature of 1 and 2, respectively. The total integrated intensity under the L-edges shows that the ψ LUMO*'s in 1 and 2 contain 20% and 28% Cu character, respectively, indicative of very covalent ground states in both complexes, although more so in 1. Two-state VBCI simulations also indicate that the ground state in 2 has more Cu (|3d8〉) character. DFT calculations show that the ψLUMO* in both complexes is dominated by O 2n- character, although the O2n- character is higher in 1. It is shown that the ligand L plays an important role in modulating Cu-O2 bonding in these LCuO2 systems and tunes the ground states of 1 and 2 to have dominant Cu(II)-superoxide-like and Cu(III)-peroxide-like character, respectively. The contributions of ligand field (LF) and the charge on the absorbing atom in the molecule (Qmol M) to L- and K-edge energy shifts are evaluated using DFT and time-dependent DFT calculations. It is found that LF makes a dominant contribution to the edge energy shift, while the effect of Qmol M is minor. The charge on the Cu in the Cu(III) complex is found to be similar to that in Cu(II) complexes, which indicates a much stronger interaction with the ligand, leading to extensive charge transfer.

Original languageEnglish (US)
Pages (from-to)8286-8296
Number of pages11
JournalJournal of the American Chemical Society
Volume128
Issue number25
DOIs
StatePublished - Jun 28 2006

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