Constants, carbonato

Hydroxo and carbonato constants. pICu" ] and pCCuxqj] were measured as functions of pH for the KOH titrations of solutions containing 0.01 M KNO3 and initial concentrations of 2.5 pM and... 

Other Coordination Complexes. Because carbonate and bicarbonate are commonly found under environmental conditions in water, and because carbonate complexes Pu readily in most oxidation states, Pu carbonato complexes have been studied extensively. The reduction potentials vs the standard hydrogen electrode of Pu(VI)/(V) shifts from 0.916 to 0.33 V and the Pu(IV)/(III) potential shifts from 1.48 to -0.50 V in 1 Tf carbonate. These shifts indicate strong carbonate complexation. Electrochemistry, reaction kinetics, and spectroscopy of plutonium carbonates in solution have been reviewed (113). The solubiUty of Pu(IV) in aqueous carbonate solutions has been measured, and the stabiUty constants of hydroxycarbonato complexes have been calculated (Fig. 6b) (90). 

Describe semiquantitatively the effect of increased pH (at constant alkalinity) or of increased alkalinity (at constant pH) on the binding of Cu(II) to soil particles. (Consider that Cu2+ forms soluble carbonato complexes.)... 

The stability constants of several carbonato complexes of metal ions in solution has been compiled (3). Several recent publications have dealt with the isolation and characterization of carbonato complexes... 

The hydration rate constant of C02, the dehydration rate constant of carbonic acid (H2C03), and p pK2 values (pTf, =6.03, pTf2 = 9.8 at 25 °C, 7=0.5 M) (63) are such that nearly 99% of dissolved carbon dioxide in water at pH < 4 exists as C02. However, these four different species may be considered as the reactive species under different pH conditions which can react with aqua metal ions or their hydroxide analogues to generate the metal carbonato complexes. The metal bound aqua ligand is a substantially stronger acid than bulk H20 ( )K= 15.7). Typical value of the p of H20 bound to a metal ion may be taken to be 7. Hence the substantial fraction of such an aqua metal ion will exist as M-OH(aq)(ra 1) + species at nearly neutral pH in aqueous medium. A major reaction for the formation of carbonato complex, therefore, will involve pH controlled C02 uptake by the M-OH(" 1)+ as given in Eq. (17). 

The latter two processes are slow as a result of which the detection of the protonated carbonato complex, and determination of its protonation constant by stopped-flow, rapid scan spectrophotometry were possible in some cases, van Eldik et al. (83) interpreted the initial spectral changes (shift of absorption maxima and the isosbestic points) of ( -cis-[Co(edda)C03l and [Co(nta)COa] at [H+]=0.05 M due to the formation of the protonated carbonato complexes, p-cis-[Co(edda)C03H] and [Co(nta)C03H], Repetitive rapid scan spectral measurements at [H + ] = 2.0 M, however, led them to the identification... 

These equations are in line with Eq. (30), such that kx denotes the ring-opening rate constant of the protonated carbonato complex and / 2 is the decarboxylation rate constant of the ring-opened bicarbonato complex. Values of these rate constants and the acid dissociation constants of some protonated carbonato complexes of cobalt(TII) (see Table III) reflect the ligand dependence with respect to charge variations, steric constraint, and donor properties of the non-labile ligands. 

Menif, R. Reibenspies, J. Martell, A. E. Synthesis, protonation constants, and copper(II) and cobalt(II) binding constants of a new octaaza macrobicylic cryptand (MX)3crystal structures of the cryptand and of the carbonato-bridged dinuclear copper(II) cryptate, Inorg. Chem. 1991, 30, 3446-3454. 

The previously unknown carbonato-complex [Ir(C03)(NH3)5]C104 has been isolated by treating [Ir(NH3)5(H20)](C104)3 with aqueous Li2C03 at pH 8.5, and the kinetics of its formation and aquation were studied.174 Stability constants have been measured using pH titration for a variety of o-coumaric acid complexes, including a 1 3 species with Ir111.74... 

Cerium(III) is considered to be a representative element for trivalent lanthanides and carbonate ions. Lanthanide carbonates are insoluble and the experimental data for the formation constants of the various carbonato species are available for Ce(III)-CC>3 system [148],... 

A similar linear regression procedure was used for the determination of carbonato stability constants. Here the equation regressed was ... 

Figure 3. Titration data for complexation of copper by carbonate. Solution contained lOmM NaHCOs and 5/xM CuSO. pH varied by adjusting Pco Curve calculated according to hydroxo and carbonato stability constants determined in...

The logarithms of the stability constants fly for the formation of 1 1 complexes of the actinide ions M +, M " ", MOj and MO with various inorganic ligands are plotted in Fig. 21.1. Carbonato complexes of alkaline-earth elements, lanthanides, actinides and other transition elements play an important role in natural waters and may stabilize oxidation states. 

Figure 10.19. Speciation of Pb(II) in the Glatt River. The concentrations given for CO2, Pb(II), Cu(II), and [Ca ] as well as for the pollutants EDTA and NTA are representative of concentrations encountered in this river. The speciation is calculated from the surface complex formation constants determined with the particles of the river and the stability constants of the hydroxo, carbonato, NTA, and EDTA complexes. The presence of [Ca " ] and [Cu " ] is considered. (From Muller and Sigg, 1990.)...

Two grams (0.005 mole) of (-)389-bis(l,2-ethanediamine)oxalatocobalt(lII) iodide3 is suspended in 30 mL of water at 35°, 0.81 g (0.005 mole) of silver acetate is added, and the mixture is stirred for five minutes at 35°. The mixture is then filtered and the precipitated silver halide is washed with 5 mL of warm water (50°). Separately, 2.4 g (0.01 mole) of sodium ciff.m-diammine-carbonato-dicyanocobaltate(UI) dihydrate is dissolved in 10 mL of water. The solution is added to the filtrate and combined with the washings. After removal of the precipitated material, the mixed solution is kept in a refrigerator, whereupon an orange diastereoisomer of the (+ )5g9 form of the carbonato complex precipitates. The product is collected on a filter and washed with cold water. Recrystallization is repeated from water until the CD peak at 24,100 cm-1 reaches a constant value. The crystals are collected on a filter, washed with 50% cold, aqueous methanol, ethanol, and diethyl ether, and finally dried under vacuum. The yield is 0.3 g. Anal. Calcd. for [Co(ox)(en)2][Co(CN)2(C03)(NH3)2]-2H20 C, 21.44 H, 5.16 N, 22.05. Found C, 21.31 H, 5.25 N, 21.78. 

Fujita et al. carried out normal coordinate analysis on unidentate and bidentate carbonato complexes of Co(IlI). According to their results the CO stretching force constant, which is 5.46 for the free ion, becomes 6.0 for the C 0, bonds and 5.0 for the C-Oj bond of the unidentate complex, whereas it becomes 8.5 for the C-Ou bond and 4.1 for the C-Ot bonds of the bidentate complex (all are UBF force constants in units of mdyn/A). The observed and calculated frequencies and theoretical band assignments are shown in Table 111-26. Normal coordinate analyses on carbonato complexes have also been carried out by Hester and Grossman and Goldsmith and Ross. ... 

The Effect of Complex Formation on the Solubility of CaCOsts) The following carbonato and hydroxo complexes and their dissociation constants at 25°C have been reported for Ca ... 

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