Structure of the diamminecopper(I) ion in solution. An X-ray absorption spectroscopic study

Abstract

X-Ray absorption spectroscopy (XAS) using synchrotron radiation has been used to probe the structure of copper(1) species in an aqueous ammonia solution that contains hydrazine to prevent any oxidation to copper(n) species. Combining a characteristic copper(1) pre-edge feature with the extended X-ray absorption fine structure (EXAFS) of the XAS enabled the stereochemistry and bond distances to be extracted for the predominant species, which is shown to be the diamminecopper(~) ion. The structure is linear with CU-N bond lengths of 1.88 f 0.02 A.Although, to a large extent, studies on the chemistry of copper have centred around the copper(11) valence state there is an increased awareness that the copper([) state also has important roles to play. Certainly, it has been known for some time that copper(1) has important functions in some life processes as exemplified in a number of metalloproteins.' In this context, studies on the inorganic chemistry of copper([) are particularly relevant, even for simple complexed species. Investigations on the XAS of copper(1) sites in simple species are especially useful because an understanding of the different spectral processes can, with advantage, be transferred to more complex systems.Copper(1) forms neutral, anionic, and cationic complexes. The strength of the copper(1)-ligand bonds increases in the order Cu-0, Cu-S, Cu-N, and whilst the highest coordination number attained is four, intermediate values of two and three are also k n o ~n . ~, ~In the older l i t e r a t ~r e , ~ twocoordination is attributed to complexes with ligands with oxygen-donor atoms and also for the acetonitrile (CH3CN) complex. However, we note that Persson et aL7 report that

Copper Oxidation/Reduction in Water and Protein: Studies with DFTB3/MM and VALBOND Molecular Dynamics Simulations

“…The standard text-book description for Cu(I) has a coordination number of four, 103 although a concrete experimental characterization is complicated by the instability of Cu(I) toward disproportionation. 104 Indeed, in the gas phase, IR studies of $\text{Cu}{({\mathrm{normalH}}_2\mathrm{O})}_n^{+}$ clusters 105,106 pointed to a linear dihydrate structure similar to Cu + diammine complex; 107 mass spectrometry study on water-Cu binding 108 also found that the binding energy of the third water and after dropped by a factor of two compared to the first two binding energies. The two-coordination configuration was supported by several theoretical calculations in the gas phase 96,97 and in CPMD/BOMD simulations for a solvated Cu(I).…”

Ab initiox-ray absorption study of copperK-edge XANES spectra in Cu(II) compounds

“…It has to be stressed that the splitting of the main resonance in peaks B and C is a common feature of several Cu͑II͒ compounds. 23,25,26,[29][30][31][32]34 Then the following tests have been performed to improve the calculation: ͑i͒ more realistic self-consistency field ͑SCF͒ potentials and ͑ii͒ the incorporation of many-body processes to compute the absorption spectrum.…”

“…1, are in agreement with previously published data. [29][30][31][32] Both FEFF8 9 and CONTINUUM 4 codes were used to calculate the Cu K-edge XANES spectra. No significant differences were found for the standard single-channel MS computations obtained by using the two different codes.…”

An X-ray absorption spectroscopic study at the mercury LIII edge on phenylmercury(II) oxygen species

“…This, together with the energies, indicates that 2p 6s(Hg) and 2p ligand orbitals are possible assignments 10,11 . In the case of copper(I) compounds at the K-edge, the intensity of the pre-edge peak is connected to the 1s 4p transitions often observed for transition metal compounds 19,20 .…”