Complex ions, spectrophotometric studies

Quantitative information about the equilibrium between olefin and Br2 on the one hand and CTC s and bromonium ion species on the other (Scheme 4) has been obtained by the already mentioned UV-Vis spectrophotometric study of the adamantylideneadamantane Br2 system (ref. 10). The spectrophotometric UV-Vis data of a large set of solutions of different reagents concentrations have been used to dissect, using a program based on NLLSQ fitting procedures, the complex spectra in those of the single species present at the equilibrium, as shown in Figure 5. 

The merocyanine form of numerous BIPS compounds in solution complex with many transition and rare-earth metal ions. The complexation between 6-nitro-8-methoxyBIPS and several ions was studied by spectrophotometric, luminescent, stopped-flow, and nanosecond laser flash photolysis techniques. The absorption maximum of the dye, 580 nm, is shifted to the 480-500 nm region, and the relatively weak fluorescence shows a similar hypsochromic shift. The kinetics of the complexation involved a fast reaction between the components, followed by a slow equilibrium of the complex to its most stable isomer. The photoreactions of the complexes include formation of a short-lived triplet state (lifetime about 2 x 10 5 s,... 

The formation of the 2 1 complexes with p-r-butylcalix[8]arene in DMF goes through several reaction intermediates, as demonstrated by a spectrophotometric study based on the weak 5Do 4— 7Fo transition of the Eu(III) ion. The overall reaction is the following ... 

Rotational Raman spectra of N2 and O2 Resonance fluorescence spectrum of Br2 Vibrational-rotational spectra of CD3H and CH3D Spectrophotometric study of stabihty of metal ion-EDTA complexes Kinetics of the H2 + I2 = 2HI reaction in the gas phase Weak-acid catalysis of BH4 decomposition Photochemistry of the cis-trans azobenzene interconversion Isotope effect on reaction-rate corrstants... 

Numerous determinations have been made of the stability constants of sulfate complexes of plutonium(IV), and the results vary by three orders of magnitude. The most plausible values (14) have come from careful ion exchange studies at I = 2 M and 25°, which indicate the presence of two species, Pu(S0i+) and Pu(S0i )2, with stepwise stability constants of 6.6 X 10 and 5.8 X 10, respectively. This Ki is in satisfactory agreement with the value 4.6 X 10 obtained potentiometrically at I = 1 M and 25° ( ). Spectrophotometric and electrophoretic studies indicate that plutonyl(VI) forms complexes containing as many as four sulfate groups, with anionic species predominating at sulfate concentrations above 1 M (15). The monosulfato complex has a reported stability constant of 14.4 as determined by extraction studies at I - 2 M and 25° (16). 

In the case of the octahedral robust complexes of cobalt (III) and chro-mium(III), substitution in the first sphere is hindered. This type of complex ion is, therefore, especially suitable for studying association in the second sphere. The hexammine and tris(ethylenediamine) cobalt(III) ions have especially been used for this kind of study. For the association of these ions with anions, such as sulfate and thiosulfate, the ion-pair constant is of the order of magnitude of 10 at 7 = 0, somewhat smaller for Coena" than for Co(NH3)6 21)y but strongly dependent on the ionic strength. Thus Posey and Taube 37) y from spectrophotometric measurements in the ultraviolet, obtain the following expression for the association constant of the ion pair [Co(NH3)6]S04 in solutions with y/Jvarying from 0.04 to 0.3 ... 

Of course, the problems of hydrolysis can be obviated by using non-aqueous solvents, and pseudo-metal ions have the necessary solubilities. For example, spectrophotometric studies (18) of complex formation equilibria between 2,2 -bipyridine (bipy) and dialkyltin dichloride have been reported. The log K values for complexes R2SnCl2-bipy are 3.19 (R, n-C4H9), 3.36 (R, CH3), and 6.7 (R, Cl) in acetonitrile. There is surprisingly little difference between the constants for dimethyl- and the dibutyltin dichloride complexes. The equilibrium constant for the dibutyl-tin dichloride complex increases with increasing dielectric constant of an alcohol solvent. 

Spectrophotometrical study of the Np(lV) in the presence of NCS ion shown that absorption maxima at 722.5 and 959.5 nm are shifted to lower energy as the NCS concentration rises, that indicates the formation of inner sphere complexes. It should be noted that Pu(IV) is not stable and is reduced to Pu(III) in the presence of NCS ions. 

Infrared absorption occurs not only with organic molecules but also with covalently bonded metal complexes, which are generally active in the longer-wavelength infrared region. Infrared spectrophotometric studies have thus provided much useful information about complex metal ions. 

A spectrophotometric study of mixed tetracyano complexes of Mo and under various pH conditions has been carried out and the protonation constants and molar extinction coefficients for Mo(OH)2(CH)4" evaluated. Polarized absorption spectra of Mo(CN)8" and W(CN)g" over the temperature range 4.2—300K have been recorded. In the crystalline state these complex ions have a quasidodecahedral co-ordination structure with the exact symmetry D2. The deviation from the ideal dodecahedral structures is appreciably smaller at low temperatures than at room temperature. Also, in contrast to previous X-ray structure determinations, it was found that the only space group the crystals can be assigned to is... 

Spectrophotometric studies of the interactions in solutions containing Ga and acetylacetonate ions show that at acetylacetone Ga ratios less than 3, hydrolysis equilibra leading to the formation of hydroxo-complexes are superimposed on the complex-formation equilibria of Ga . ... 

The trans isomer, on the other hand, interacts monofunctionally at the N-7 and N-1 of adenine and the N-3 of cytosine. Both isomers react monofunctionally with the N-7 of guanine and hypox-anthine. X-ray diffraction studies of the complexes formed between cis Pt(NH3)2X2 and various bases have confirmed some of the conclusions obtained from the early spectrophotometric studies. The product of the reaction between inosine and Pt(NH3)2l2 consist of two hypoxanthine rings bound to the platinum ion via the N-7 position (25). A similar structure results from the interaction of PtCl2 (en) with guanosine (26,27) again the N-7 position becomes occupied by the metal. 

The reaction of zirconium and hafnium with thiocyanate ion was studied spectrophotometrically 214) at thiocyanate concentrations over the range 0.002 to 0.18 M, free perchloric acid concentrations of 0.1 to 0.8 M, and at high metal ion concentrations. Experiments were interpreted to show that a series of complexes from MNCS + to M(NCS)4 were formed. At high thiocyanic acid concentrations, the zirconium is converted to an anionic species much more readily than the hafnium. 

The formation constant of the NiCf complex has been determined by a spectrophotometric study at 298.15 K in concentrated HCl (4.4 - 10.67 M) and LiCl (2.94 - 12.46 M) solutions, and the formation constant of the NiCl2 complex was tentatively estimated. The method used by the author results in a semi-thermodynamic constant, in which the activity of chloride ion is considered, but the ratios y. 2, and /yNicij were assumed to be nearly constant with... 

Experiments are under way for the production of ion-selective membrane electrodes that can also be used in non-aqueous solutions, and studies are being made of the possibilities of application of liquid junction-free potentiometry in non-aqueous solutions. High-performance computer evaluation procedures permit the employment of spectrophotometric equilibrium measurements in the study of complex systems. Spectrophotometric measurements are not prone to greater errors in non-aqueous solutions than in water. 

F Spectrophotometric Kinetic Methods 381 14G Spectrophotometric Studies of Complex Ions 384 Questions and Problems 390... 

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