Copper visible spectroscopy

The copper atom-acetylene matrix-reaction, monitored originally by esr spectroscopy (60) has now been investigated by IR/UV-visible spectroscopy (144), and there is general agreement on the identification of two mononuclear species, CuCCaHali.. The esr/IR/UV-visible... 

Raman and UV-visible spectroscopy, but no precise characterization was made. A report was made in 1981 where the IR spectrum of Cu atoms deposited with C02 at 80 K was interpreted in terms of the formation of a -coordinated complex between C02 and zerovalent copper [32]. Almond et al. [33] prepared a (C02) M(CO)5 molecule (M = Cr, W), that led to the formation of CO and oxometal carbonyl under UV irradiation. The first complete study of the reactivity of C02 with the first row of transition metals was made by Mascetti et al. [34, 35]. Here, it was shown that the late transition metal atoms (Fe, Co, Ni, and Cu) formed one-to-one M(C02) complexes, where C02 was bonded in a side-on (Ni), end-on (Cu), or C-coordinated (Fe, Co) manner, while the earlier metal atoms (Ti, V, and Cr) spontaneously inserted into a CO bond to yield oxocarbonyl species OM(CO) or 0M(C0)(C02). Normal coordinate analysis showed that the force constants of CO bonds were significantly decreased by 50%, compared to free C02, and that the OCO angle was bent between 120 and 150°. 

Preservation of the zeolite structure was verified by X-ray powder diffraction (XRD) patterns recorded on a CGR Theta 60 instrument using Cu Kcq filtered radiation. The chemical composition of solids was determined at the Service Central d Analyse CNRS (Solaize, France). Copper in the zeolite was characterised by DR-UV-visible spectroscopy using a Perkin-Elmer Lambda 14 apparatus, equipped with a reflectance sphere, and by temperature programmed reduction (TPR), using a Micromeritics Autochem 2910, equipped with a katharometer (3% H2/Ar gas mixture at 30 mL.min1 and 10 K.min 1). 

The effect of metal ion stereochemical preference in mediating the final structure of a self-assembling helix was examined by Williams and coworkers using the ligand (20) [26]. The formation of a double-hehcal structure is seen from the reaction of two equivalents of copper(I) and two equivalents of (20) (Figure 8). This structure, with pseudotetrahedral geometry around the metal centers, was found to exist in solution by UV-visible spectroscopy, H NMR and cyclic voltammetry. The double helix does not appear to be the only species existing in solution mononuclear [Cu(20)J+ was observed by H NMR spectroscopy. The H NMR spectrum of the complex between copper(I) and... 

The crystals that are obtained from the cluster formation reactions are intensely colored. In fact, the intensity of the color increases when going from sulfur- to selenium- to tellurium-bridged compounds (see below), as might be expected for an increase in the covalent or (semi-) metallic binding properties. Small copper sulfide and selenide clusters form light red, orange, or purple crystals, but with increasing cluster size the color varies from dark red to reddish-black to (finally) black with a metallic sheen. The optical spectra of some copper selenide cluster compounds have been studied by means of solid-state UV-visible spectroscopy. 

Preparation of the copper-free [2]-rotaxane, Copper(I)-free [2]-rotaxane I5+PF5 was obtained by treatment of 122+(PF5 )2 with excess KCN (see Figure 9). Care had to be taken to avoid both large excess of KCN and too long reaction times, which were responsible for some decomposition as shown by TLC and UV-visible spectroscopy. 

Two more complexes were obtained with the dianion 26 as a ligand. These complexes were characterized by X-ray diffraction, UV/visible spectroscopy, and electrochemical measurements [69b]. The Cu(II) complex with the dianion plus four coordinated water molecules and two molecules of water of hydration molecules forms a polymeric chain with the copper atoms linked to the two nitrile groups of the ligand. The complex of copper (I) with the fr s-substituted ligand... 

Addition of two equivalents of ethynylferrocene to [MCl2(PR3)2] in the presraice of copper(I) iodide and diethylamine produces bis(acetylides) there is some evidence for interacdmi of the palladium or platinum and the iron centres from UV-visible spectroscopy. 36 j je bridging ethyne-diyl complex [PdCl(PR3)2]2(p-CsC) (R = Et, Bu) reacts with phenylisonitrile by double insertion at one of the metal centres producing [PdCl(PR3)2](p-CsCC =NPh C =NPh))[PdCl(PR3)2]. In the presence of 0.2 equivalents of added phosphine ligand the insertions occur symmetrically, one at each metal centre. The crystal structure of the triethylphosphine containing product was rtetermined. The use of two equivalents of added phosphine ligand produces the symmetrical dication [Pd(PR3)3](p-C =NPh CsCC =NPh )[PdCl(PR3)2] [C1]2.137... 

Fluorescence, EPR, CD, and UV-visible spectroscopy studies suggest that both copper complexes share the same structures in the solid state and in solution. 

PhI=NTs in MeCN affords a copper species that is indistinguishable by ultraviolet-visible (UV-vis) spectroscopy from an identical solution derived from Cu(OTf)2. Given the strong oxidizing nature of PhI=NTs, it seems likely that both catalysts proceed through a Cu(II) species. Beyond this, little can be said with certainty. If nitrenoid formation proceeds by a two-electron oxidation of the catalyst, one would need to invoke Cu(IV) as an intermediate in this process (77). This issue is resolved if one invokes the intervention of a bimetallic complex in the catalytic cycle. However, attempted observation of a nonlinear effect revealed a linear relationship between ligand enantiopurity and product ee (77, 78). 

The d-d absorption of the copper complex differs in each step of the catalysis because of the change in the coordination structure of the copper complex and in the oxidation state of copper. The change in the visible spectrum when phenol was added to the solution of the copper catalyst was observed by means of rapid-scanning spectroscopy [68], The absorbance at the d-d transition changes from that change the rate constants for each elementary step have been determined [69], From the comparison of the rate constants, the electron transfer process has been determined to be the rate-determining step in the catalytic cycle. 

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