Absorption spectrum, mixed metal

Infrared spectroscopy is not as inherently informative with regard to metal interactions in highly symmetrical metal-metal bound dimers as is Raman spectroscopy, since the totally symmetric metal-metal stretch is a forbidden absorption in the infrared experiment. Oldham and Ketteringham have prepared mixed-halide dimers of the type Re2ClxBr 2xto lower the symmetry and hence introduce some infrared allowedness into the Re-Re stretching mode (206). Indeed, the appearance of a medium-intensity band at 274 cm 1 in the infrared spectrum of the mixed-halo species was considered to be the result of absorption by the metal—metal stretching vibration, which was also observed in the Raman spectrum at 274 cm ". ... 

Its absorption spectrum shows one band at 320 nm (e = 2900 M 1cm 1), assigned to the cti - ct2 transition localized in the Au-Tl moiety. The emission spectrum in the solid state at 77 K shows a band at 602 nm, which is attributable to a transition between orbitals that appear as a result of the metal-metal interaction. In this sense, Fenske-Hall molecular orbital calculations indicate that the ground state is the result of the mixing of the empty 6s and 6pz orbitals of gold(I) with the filled 6,v and the empty 6pz orbitals of thallium(I). In frozen solution, this derivative shows a shift of the emission to 536 nm, which has been explained by a higher aggregation of [AuT1(MTP)2] units in the solid state if compared to the situation in solution. 

Finally, 1-electron oxidation of [Fe2Rc(CO)i23 with tropilium bromide has been reported to give a neutral mixed-metal cluster formulated as [Fe2Re(CO)i2]2 on the basis of elemental analyses (67) however, its IR spectrum, which shows carbonyl absorptions quite similar to those of the starting material, is inconsistent with such a formulation. 

Another important application of selective extra absorption is the use of chemical shifts in the various X-ray emission channels. This opportunity yields the possibility of measuring the valence-selective X-ray absorption spectra, both XANES and EXAFS. This technique has been applied successfully to Fe(III) as a test case (Glatzel et al., 2002). At least in principle, many applications of this methodology are possible. A metal will have a different X-ray emission spectrum than an oxide. This difference can be used to measure the X-ray absorption spectra of the metal and the oxide in a mixed metal oxide. Such mixtures are encountered frequently in heterogeneous catalysis. 

Electrochemical investigation of [ThMoi2042] " reveals no stepwise reduction of the anion to isostructural mixed-valence heteropoly blues that is observed for many other POMs, but rather an irreversible multi-electron reduction, correponding to decomposition of the anion [20], This behavior is anticipated for polyoxometalates in which the metal has a m-dioxo environment ( type 11 structure [21]). However, cyclic voltammograms of [UMo 12042] show a reversible one-electron oxidation to the uranium(V) analog [20] at +0.90 vs see at pH 0. The electronic absorption spectrum of the oxidized species has been reported. 

Heterobimetallic and polymetallic structures featuring bridging acet-ylides can also be prepared from the respective Cu(I), [or Ag(I)], and Re(I) substmctures described above. Excitation of both the penta- (224, 230) and decanuclear (203) mixed-metal alkynyl complexes in the solid state and in solution at X > 400 nm results in strong red luminescence (680-700 nm) characteristic of predominantly [i Ti(Re) ti (NN)] MLCT excitation mixed with ti(C=C) —> 7t (NN) LLCT perturbed by the Mg or Mg cores of the components. The MLCT state energy in the absorption spectrum for M = Ag(I) is shghtly blue-shifted relative to M = Cu(I) due to the poorer donating ability of the Agg versus Cug core, which causes the Re(I) center of the [Re(CO)g(NN)]" fragment to be less electron rich. 

Luminescent coordination compounds continue to attract considerable attention. Zink recently reported a new mixed-ligand copper(I) polymer that shows interesting photoluminescence (232). The complex [CuCl(L44)Ph3P] consists of a one-dimensional chain lattice of metal ions bridged by both Cl" ions and pyrazine molecules. The compound shows conductivity of less than 10-8 S cm 1. The absorption spectrum of the complex shows a band at 495 nm, which could be interpreted as the promotion of an electron from the valence band to the conduction band. On the basis of resonance Raman spectra, the lowest excited state in the polymer is assigned to the Cu(I)-to-pyrazine metal-to-ligand charge-transfer excited state. 

Colorless to pale yellow, oily liq very hygroscopic turns brown on exposure to air or light. Acrid burning taste. Develops odor of pyridine. bp745 247 (partial decompn) bp 123-125. Volatile with steam. 1.5282. df 1.0097. [c - 169. pK, (153 6.16 pRj 10.96. pH of 0.05M soln 10.2. Forms salts with almost any add and double salts with many metals and adds. Absorption spectrum Purvis, J. Chem. Soc. 97, 1035 (1910) Dobbie, Fox, ibid. 103, 1194 (1913). Misc with water below 60° on mixing nicotine with water the volume contracts. Very sol in ale, chloroform, ether, petr ether, kerosene, oils. Distribution of nicotine between water and petroleum oils Norton, Ind. Eng. 

Pulse radiolytic studies of the kinetics of formation of clusters containing two different metals are more readily accessible, for the reasons given above, when both ions may be reduced by a monoelectronic process. This can be achieved with mixed solutions of the monovalent ions Ag and Au, in the form of KAg(CN)2 and KAu(CN)2. " The evolution of the optical absorption spectrum with time was followed specifically at 400 and 520 nm, which correspond to the maxima of the surface plasmon bands of the monometallic silver and gold clusters, respectively. The early steps of the mechanism are rapid reductions of Ag and Au into atoms... 

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