Spectral characteristic of complexes

The absorption bands characteristic for solvating molecules B have been distinguished in the spectra of Cp2Ln(B) and (Me5C5)2Ln(B) (Ln = Eu, Yb). The THF molecules absorb at 2980, 2880 cm and in the region 1240 840 cm [1, 14, 19]. However, the intensity of the bands is similar to the weak bands of metallocenes [1], that is why there are some difficulties in the determination of the complex composition. The bands at 1058 [19] and 1032 cm [14] are assigned to coordinated DME and Et20, respectively. 

The spectrum of the ytterbium-platinum complex (MegC5)2Yb( x-C2H4)Pt(PPh3)2 exhibits a superposition of initial ytterbium and platinum complexes which testifies the weak coordination interaction . ..CH2=CH2 [86]. It is also confirmed by the H NMR spectroscopy data. It is interesting that the absorption band of feC bond is absent in the spectrum of ytterbium complex with dimethylacethylene (Me5C5)2Yb(MeOCMe) [87]. 

The PMR data, just as IR spectroscopy, confirm the ionic character of the bond between metal atom and Cp ring. For instance, the chemical shift of diamagnetic Cp2Yb (8 5.64 ppm) insufficiently differs from that of magnesium (8 5.79 ppm) and sodium (8 5.53 ppm) Cp derivatives, but is significantly larger than for ferrocene (8 4.08 ppm) [17]. 

An additional information on the structure of REM complexes can be obtained from the absorption spectra in visible region. The special feature of Cp2Ln compounds is that they exhibit the spectra in the region 300-5-650 nm (typical for Ln cation) and does not absorb in the region 650-5-1200 nm (the region characteristic for Ln ) [4, 17, 19]. 

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The dihalogen complexes with olefin donors were first identified spectroscopically in the mid-1960s [42-45] and extensive experimental and computational studies have been carried out by Chiappe, Lenoir and coworkers in recent years [46 - 48 ]. These systems are highly unstable, since the complexation of dihalogens with olefins is followed rapidly by the formation of ionic intermediates and further chemical transformations. Therefore, attention in the corresponding work has mostly focused on hindered olefins, although the spectral characteristics of complexes with less sterically crowded and alkyl- as well as chloro-substituted and cyclic olefins are also reported [44]. The absorption maxima for the dihalogen complexes with olefins (evaluated by the subtraction... 

The main problem of elementary chemical reaction dynamics is to find the rate constant of the transition in the reaction complex interacting with its environment. This problem, in principle, is close to the general problem of statistical mechanics of irreversible processes (see, e.g., Blum [1981], Kubo et al. [1985]) about the relaxation of initially nonequilibrium state of a particle in the presence of a reservoir (heat bath). If the particle is coupled to the reservoir weakly enough, then the properties of the latter are fully determined by the spectral characteristics of its susceptibility coefficients. 

Table 1 Formation constant and spectral characteristics of bromide (charge-transfer) complexes with various acceptorsa...

Electrochemical experiments allow the determination of complex stability constants for Fe2+ by measuring complex redox potentials over a range of pH values. The Fe34YFe2+ redox potential of the siderophore complex, as with the spectral characteristics of the complex, is dependent on the inner coordination environment of the iron. These considerations will be addressed later (Section III.D). 

Determination of changes in the absorbance (AA) of a solution of the complex containing a quencher can be investigated when a pulse of laser light excites Ru(bpy)j+. The principal spectral characteristics of the complex and its derived transient species are given in Table 10.3. 

The abovementioned data show that the spectral characteristics of C60/PVP complexes vary depending on the PVP molecular mass and fullerene content in the complex. Therefore, the quantitative determination of fullerene concentration in such complexes by measuring their absorbance at 336 nm without extraction (Lyon et al., 2006) can give non-reliable results. For quantitative analysis of fullerene in such complexes we used the heterophase and homophase methods, based on destruction and isolation of pure fullerene C60 (Krakovjak et al., 2006). The choice of the method was determined by fullerene concentration - at concentration less... 

Intermediates for the 0 Complexes. The results obtained on the oxygen forms of the compounds studied revealed a similar set of intermediates, AS, B, C and D, though the spectral parameters and rates associated with formation of the intermediates are in many cases noticeably different from those of the CO forms. As C and D are postdissociative intermediates, it would be expected that the spectral characteristics of these intermediates should be fairly... 

The complex and diverse fragmentation pathways of methyl maltol and methyl allomaltol prompted a study of the mass spectral characteristics of other methoxypyran-4-ones... 

ESR examination of nonchemically isolated fulvic acids showed that Mn2+ was the primary paramagnetic species observable (60, 61). Most likely, the soluble-colloidal fraction we identified in the speciation studies consisted primarily of such complexes. Because the ESR spectral characteristics of Mn in fulvic acid complexes are quite similar to Mn(H20)62+, Alberts et al. (62) suggested that the metal-fulvate interaction was weak. Stronger interaction would be expected to lead to changes in peak shape. This view leaves unexplained the ability of the complexes to survive the isolation procedure s long ultrafiltration steps, because weak interactions are usually associated with reversible complexation. 

Oquist, G., Fork, D.C., Schoch, S. and Malmberg, G. 1981. Solubilization and spectral characteristics of chlorophyll-protein complexes isolated from the thermophilic blue-green alga Synechococcus lividus. Biochim Biophys. Acta, 638.192-200. 

Most importantly, the spectral characteristics of the charge-transfer (CT) absorption band also provide a quantitative measure of the electronic coupling element in the intermolecular complex, i.e. [14-16] ... 

The related nitrene(imido)-oxo complex [Re(NPh)(Et2dtc)2]20 is known (Section 43.7.4), and can be prepared by the action of aniline on Re203(Et2dtc)4 in refluxing benzene.121 The oxo-sulfido derivative Re202S[(PhCH2)2dtc]2 can be isolated as brown needles in low yield as one of the products from the reaction between ReCl(CO)5 and tetrabenzylthiuram disulfide in benzene. The IR spectral characteristics of this complex include r(Re=0) at 895 cm-1 and v(Re—S—Re) at 448 and 435 cm-1.252... 

The apparent contradiction between the empirical stoichiometry and the spectral characteristics of these new uranyl complexes was finally resolved by X-ray crystallography. Specifically, a single crystal X-ray structural analysis of the blue-black material formed from the reaction of the anhydrous uranyl chloride and o-dicyanobenzene [112] (Figures 22 and 23) revealed that the complex obtained was in fact an expanded five-subunit superphthalocyanine macrocycle in which a pentagonal bipyramidal coordination geometry pertains about the centrally-bound uranium atom. 

Fia. 9. Spectral characteristics of the soluble NADH dehydrogenase (1.6 mg/ml) isolated from complex I. Traces 1, spectrum of oxidised enzyme 2, NADH-reduced enzyme 5, dithionite-reduced enzyme 4, flavin contribution to 1 after destruction of iron-sulfur chromophore with sodium mersalyl 3, iron-sulfur contribution to l obtained by subtraction of 4 from 1 6, 4 plus dithionite showing that after destruction of the iron-sulfur chromophore with mersalyl and reduction of flavin with dithionite the enzyme has no absorption in the visible region. From Hatefl and Stempel (40). 

Table 1 Visible and CD spectral characteristics of aqueous ferric siderophores and of a model complex...

Somewhat more complicated than the complexes discussed earlier is the combination of water with ammonia. The IR spectral characteristics of this complex were calculated using a variety of basis sets and the results are presented in Table 3.49. Also presented in this table are comparable data computed at a correlated (MP2) leveF, for purposes of comparison. The red shift of the proton donor water molecule v. band is 103 cm , quite a bit lower... 

They considered not only these qualitative aspects of the IR spectrum but also the quantitative changes in the absorbance with loading of metal complex to conclude that 1) the disappearance of the 1552 cm peak is related to the mechanism that causes the disappearance of the 785 cm fundamental vibration. The adsorbed complexes in intimate contact with the surface contribute no absorption peaks of the complex in the spectral region below 1000 cm Thus, the disappearance of the 785 and 1552 cm vibrations are characteristic of complexes in close contact with the surface. 

The UV-vis spectrum of the FeBd2Gm(BF)2 complex also proved to be quite unexpected since it contains only one band with an intermediate Vmax value ca 21 550cm-i, rather than two bands at 22 730 and 20 880 cm-i. With this complex, maximal tension in n-systems of different dioximate fragments has presumably been observed. Since UV-vis spectral characteristics of the FeDm3(BF)2 and FeGm3(BF)2 complexes are identical in the visible region, the CTB in the spectrum of the nonsymmetric FeDm2Gm(BF)2 clathrochelate is nearly the same as that of the first two complexes. To the contrary. 

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