Complexation constants

An alternate and fonnally very powerfiil approach to resonance extraction is complex scaling [7, 101. 102. 103. 104. 105. 106 and 107] whereby a new Hamiltonian is solved. In this Hamiltonian, tlie grid s multidimensional coordinate (e.g., x) is multiplied by a complex constant a. The kinetic energy gains a constant complex factor > (1/a )(d /dx )), while the potential needs to be evaluated at points with a complex... 

For example, in HCl (aq), the following chlorocomplex ions are known and stabiUty complex constants have been determined (105). 

The template effect has long been accepted prima facie by workers in the crown field because of the obvious relationship between ring size and complexation constant. In fact, Cram stated in 1975 that the templating properties of for preparing crown ethers is well established.. . In fact, the template effect was widely acknowledged and has always received overwhelming support. Nevertheless, few direct comparisons are available in the literature and we have restricted ourselves m this discussion only to direct rather than the large body of presumptive evidence which is currently available. 

Therefore it was generally assumed that 18-crown-6 (n = 6) forms the tightest5 arenediazonium complexes. However, this assumption is wrong on the basis of quantitative data on complexation equilibria the largest complexation constants K are obtained with 21-crown-7, not with 18-crown-6 (see Sec. 11.2). 

Kuokkanen (1985) determined complexation constants for 4-tert-butyl- and 4-chlorobenzenediazonium tetrafluoroborate with polyethylene glycols of average molecular mass 300, 600, 1000, and 2000 under the same experimental conditions as mentioned above. The constants are significantly lower than those with... 

Measurement of complexing constants by radiochemical methods. S. Hubert, M. Hussonnois and R. Guillaumont, Struct. Bonding (Berlin), 1978, 34, 1-18 (29). 

Where do we stand Many needed complexity constants are unknown or poorly known. Questions of solubility under a variety of circumstances remain largely unanswered. Prof. Fuger summed... 

The first question is of interest for sequestering heavy metal ions, e.g., to stabilize peroxides, or for the masking of water hardness. The complex constant... 

The dissoziation of the complex may be altered by different temperatures or shift in pH. Therefore it is necessary to determine the complex constant using different conditions. 

As mentioned earlier, radicals that do not react can go on a random walk and may meet later at time [Pg.72]

Equilibrium complexation constants for Cu reactions with natural organic matter and the details of Cu speciation are bound to remain somewhat uncertain, since the composition of the complexing molecules varies from site to site. What is not in dispute is that the fraction of dissolved copper present as free aquo Cu is probably very small in any natural water. In extremely pristine waters, hydroxide and carbonate complexes may dominate, but organic complexes usually dominate in waters containing more than a few tenths of a mg/L organic carbon. 

Hubert S, Hussonois M, Guillaumont R (1978) Measurement of Complexing Constants by Radiochemical Methods. 34 1-18... 

The Kmax (and K, see below) constants determined from steady-state kinetic measurements are thus seen to be complex constants containing two or more of the individual rate constants illustrated in Fig. 2. 

This is a reasonable inference, because site binding is significant only with multivalent cations and strong electrostatic interactions. Under these conditions ion polarization occurs and bonds have some covalent character (Cotton Wilkinson, 1966). This is illustrated by the data of Gregor, Luttinger Loebl (1955a,b). They measured the complexation constants of poly(acrylic acid), 0 06 n in aqueous solution, with various divalent metals, which, as it so happens, are of interest to AB cements (Table 4.1). The order of stability was found to be... 

Metal ion Crystal ionic radius A Complexation constant... 

The complexation constant for copper(II) is particularly high and Wall Gill (1954) have suggested that chelate formation takes place with two carboxyl groups ... 

A typical inorganic redox system of this type involves the equilibrium between metallic copper and copper(II) ions. In the absence of a complex-former the disproportionation constant is large and a solution of Cu+ ions is very unstable. However, in the presence of ammonia, copper(I) ions are bonded in a complex, constant K decreases and the -j8 curve exhibits three inflection points. 

Table 1. H-NMR results for the determination of the complexing constant (Kc) for TBSM/MA mixtures...

When the Zincon ion-pair is exposed to an aqueous sample containing the analyte, the latter diffuses into the sensor membrane to react with the indicator, and gives a colour transition from pink to blue at near neutral pH. The pKa value of Zincon for the color transition from pink to blue is above 13, therefore, the sensor membrane is virtually insensitive to pH changes. However, due to the high complexation constant of Zincon for copper and zinc, the response of sensor membrane is irreversible and must be evaluated kinetically12. 

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