| Abstract
| - Single- and multiple-scattering (MS) X-ray absorption fine structure (XAFS) analysis of veterinary antiinflammatory Cu(II) complexes of indomethacin (1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid = IndoH) of the general formula [Cu2(Indo)4L2] (L = DMF, NMP, DMA, OH2), and [Cu2(OAc)4(OH2)2] are reported. MS XAFS analysis has, for the first time, successfully fitted to XRD data the coordination geometry of such Cu(II) dimer complexes using a centrosymmetric model, as well as determined new structures. However, symmetry lowering hydrogen-bonding characteristics of the aqua adduct necessitated the removal of symmetry restraints to obtain reasonable fits.
- Copper K-edge X-ray absorption spectroscopic (XAS) measurements were recorded for the veterinary antiinflammatory Cu(II) complexes of indomethacin (1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid= IndoH), of the general formula [Cu2(Indo)4L2] (L = N,N-dimethylformamide (DMF), N,N-dimethylacetamide(DMA), N-methylpyrrolidone (NMP), and water), and [Cu2(OAc)4(OH2)2] at room temperature and 10 K. Thebond lengths and bridging O−C−O angles of the dimeric Cu(II) cage (Cu2O10C8) obtained from the multiple-scattering (MS) fitting of the X-ray absorption fine structure (XAFS) using a centrosymmetric model of [Cu2(Indo)4(DMF)2] gave Cu···Cu = 2.62(2) Å, mean Cu−OAc = 1.95(2) Å, Cu−OL = 2.15(2) Å, bridging O−C−O= 125(1)°, Cu displacement from plane 0.19 Å compared with the XRD data Cu···Cu = 2.630(1) Å, meanCu−OAc = 1.959 Å, Cu−OL = 2.143(5) Å, bridging O−C−O angles = 123.2(5)°, Cu displacement from plane0.20 Å. The excellent agreement between the XAFS- and XRD-derived data allowed the structures of related[Cu2(Indo)4L2] (L = DMA, NMP) complexes to be determined. All display a similar Cu2O10C8 coordinationgeometry, which is independent of the nature of the axial ligand. While XAFS analysis of [Cu2(Indo)4(OH2)2]and [Cu2(OAc)4(OH2)2] indicates a coordination geometry similar to that of [Cu2(Indo)4L2] (L = DMF, DMA,NMP), removal of symmetry restraints in the MS model is required to obtain axial bond lengths comparable tothose derived in the XRD structures of the acetate complex. For the Indo complex, the fitted bond lengths withthe lower symmetry model give a mean Cu−LOH2 bond distance within experimental errors of the value for[Cu2(Indo)4(DMSO)2] (2.16(2) Å) (XRD). The difficulty in refining the Cu−O(OH2) distance of [Cu2(OAc)4(OH2)2]and [Cu2(Indo)4(OH2)2] using a centrosymmetric MS model is attributed to a symmetry reduction due to hydrogen-bonding effects characteristic of the aqua adducts, as is observed in the XRD structure of the acetate complex.
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