Metallic complexes absorbers

Transition metal complexes absorb radiation and exhibit both fluorescence and phosphorescence. In certain cases the fluorescent and phosphorescent yields have been related70 to zero-order crossings in... 

Typical cations which undergo photoreduction via electron transfer include Hg2+(Amax = 1800 A), Cu2 + (Anwx = 2000 A), Pb2+(Amax = 2085 A), Fe3+(Amax = 2300 A) and Ce4+(Amax = 3200 A) (16). When these cations are complexed with anions to form ion pairs, their absorption spectra are shifted toward the visible region. Therefore transition metal complexes absorb even visible light. The mechanism of radical formation can be considered to be an electron transfer reaction between cations and anions as follows,... 

Nitrato-metal complexes absorb in the regions 1530-1480 cm (6.54-6.76pm) and I290-I250cm (7.75-8.00pm)due to the asymmetric and symmetric vibrations respectively of the NO2 group. 

The absorbance table at X for each of the metal complexes constitutes a matrix with rows of absorbances, at one wavelength, of Mo, Ti, and V complexes, in that order. Each column comprises absorbances for one metal complex at 330, 410, and 460 nm, in that order ... 

If there is no wavelength where only the metal-ligand complex absorbs, then the measured absorbances must be corrected for the absorbance that would be exhibited if the metal and ligand did not react to form ML, . 

Flowever, transition metal complexes do absorb in the visible region, giving them a characteristic colour. Flow can this happen if the transitions are forbidden The answer is that interaction may occur between the motion of the electrons and vibrational motions so that some vibronic transitions are allowed (see Section 7.3.4.2b). 

Studies of the base-hydrolysis mechanism for hydrolysis of technetium complexes have further been expanded to an octahedral tris(acetylacetonato)techne-tium(III) [30], Although a large number of studies dealing with base hydrolysis of octahedral metal(III) complexes have been published [31], the mechanism of the tris(acetylacetonato)metal complex is still unclear. The second-order base hydrolysis of the cationic complex tris(acetylacetonato)silicon(IV) takes place by nucleophilic attack of hydroxide ion at carbonyl groups, followed by acetylacetone liberation, and finally silicon dioxide production [32], The kinetic runs were followed spectrophotometrically by the disappearance of the absorbance at 505 nm for Tc(acac)3. The rate law has the following equation ... 

Levelling acid dyes and particularly 1 1 metal-complex types generally require an exceptionally low pH in order to promote exhaustion and levelling up to 3% o.w.f. sulphuric acid is most commonly used for levelling acid dyes, although hydrochloric, formic and phosphoric acids are also effective. In the case of conventional 1 1 metal-complex dyes it is essential to use a sufficient excess of acid over and above the typical 4% o.w.f. sulphuric acid normally absorbed by the wool, otherwise there may be a tendency towards tippy dyeings and lower wet fastness. The actual excess required depends on applied depth and liquor ratio [2] typical recommendations are given in Table 12.2. 

In the 2 1 complexes, bathochromicity increases in the order Ni2+< Co3+< Cr3+. In contrast, the 1 1 Cu2+, Ni2+, Cr3+, and Co3+ metal complexes exhibit similar spectral curves to one another, absorbing at shorter wavelength than the corresponding 2 1 complex dyes.22... 

Bruce C. Gates, Supported Nanostructured Catalysts Metal Complexes and Metal Clusters Ralph T. Yang, Nanostructured Absorbents... 

To obtain data for use with this equation, a series of solutions can be prepared in which the concentration of B is kept constant but the concentration of A is varied. For each of these solutions, the concentration of the complex [A Bm] is measured as a function of [A]. For many complexes, the concentration of the complex can be measured by spectrometry because many complexes absorb at a wavelength that is different from that of the metal ion or ligand alone (see Chapter 18). When [B] is kept constant, Eq. (19.5) reduces to... 

The method is either not affected by or can allow for interference from phosphate, sulfate, carbonate, bicarbonate, nitrate, coloured metal complexes, ammonia dyes, detergents, phenols, and other ultraviolet-absorbing substances. The method incorporates three features designed to reduce interferences ... 

One possibility to obtain a relatively small leakage into the substrate is to introduce a thin film of metal or absorbing layer such as a polymer or a dye with a complex dielectric function, or a thin layer of low refractive index material... 

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

The metal complexes of the d-block elements absorb light due to electronic transitions occurring between d-orbitals of the metal species, or because of charge transfer within the complex. 

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