Copper complexes absorption spectra

Unfortunately, addition of copper(II)nitrate to a solution of 4.42 in water did not result in the formation of a significant amount of complex, judging from the unchanged UV-vis absorption spectrum. Also after addition of Yb(OTf)3 or Eu(N03)3 no indications for coordination were observed. Apparently, formation of a six-membered chelate ring containing an amine and a ketone functionality is not feasible for these metal ions. Note that 4.13 features a similar arrangement and in aqueous solutions, likewise, does not coordinate significantly to all the Lewis acids that have been... 

Figure 11.10 Absorption spectrum of the protein-copper complex of the biuret reaction.

The blue color of these "type 1" copper proteins is much more intense than are the well known colors of the hydrated ion Cu(H20)42+ or of the more strongly absorbing Cu(NH3)42+. The blue color of these simple complexes arises from a transition of an electron from one d orbital to another within the copper atom. The absorption is somewhat more intense in copper peptide chelates of the type shown in Eq. 6-85. However, the -600 nm absorption bands of the blue proteins are an order of magnitude more intense, as is illustrated by the absorption spectrum of azurin (Fig. 23-8). The intense blue is thought to arise as a result of transfer of electronic charge from the cysteine thiolate to the Cu2+ ion.520 521... 

Bis( 1,10-phenanthroline)copper(I) has an absorption spectrum which is a function of concentration. This has been attributed to oligomerization, possibly via n—K intermolecular stacking interactions. The tendency to oligomerize has a marked effect on the electrochemistry of the complex. For example, the complex exhibits extensive adsorption on the surface of a graphite electrode. The multilayers exhibit good electron mobility and the layers probably grow by reduction of surface copper(II). Rotating disc voltammetric measurements of the reduction of... 

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. 

These experimental results prompted reconsideration of the inscrutable result reported for Cu(SC5H4-p-N02)(HB(3,5-Me2pz)3) (36). The absorption spectrum of the complex was reasonably similar to that of type I copper, whereas the EPR spectrum was typical for a tetragonal complex. Because the EPR was recorded in THF at 77 K, our observa-... 

Figure 7. Ground-state wave function of plastocyanin. A HOMO wave function contour for plastocyanin (28). B HOMO wave function contour for the thiolate copper complex tet b (34/ C Copper L-edge (38) and sulfur K-edge (34) spectra as probes of metal-ligand covalency. D Absorption, single-crystal polarized absorption, and low-temperature MCD spectra of plastocyanin. The absorption spectrum has been Gaussian resolved into its component bands as in reference 33.

S-Diketones which contain aliphatic, aromatic, or heterocyclic radicals as well as a selenienyl radical have in the UV spectrum two characteristic absorption maxima (280 and 300 m/a) and high absorption intensity almost equal to that of their copper complexes. In the... 

The CT state was found to decay rapidly (Figure 27c), with a lifetime of 50 ps, leaving a residual absorbance which was identified as the Au porphyrin neutral radical by virtue of its differential absorption spectrum. This latter species decayed relatively slowly, with a lifetime of 2.5 ns, to re-form the ground state of Cu.20. As above, the rapid deactivation of the CT state is ascribed to a combination of direct reverse electron transfer (Eq. 18) and oxidation of the central copper(I) complex by the Zn porphyrin 7r-radical cation (Eq. 19). The yield of the Au(III) porphyrin neutral radical which escaped direct electron transfer was estimated from the transient absorption spectral changes to be 90 %. Thus, direct reverse electron transfer (/ i8 = 2.0 X 10 s ) accounts for only 10 %, and electron abstraction from the central copper(I) complex k g = 1.8 x 10 s ) is the dominant decay route. The residual Au porphyrin neutral radical decays over several nanoseconds due to electron donation to the copper(II) complex (Eq. 20). 

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