Complex formation constant, outersphere

Complexes, see also specific type in solution, structures, see X-ray diffraction n-Complexes, 4 178-184 Complex formation constant, outersphere, 43 46, 55 electrovalent interaction in, 3 269-270 Compressibility coefficient of activation, 42 9 Comproportionation constants, class II mixed-valence complexes, 41 290-292 Comproportionation equilibrium, 41 280-281 Compton effect, 3 172 Conantokins, calcium binding, 46 470-471 Concanavalin A, 36 61, 46 308 Concensus motif, 47 451 Concentration-proportional titrations of poly-metalates, 19 250, 251, 254 Condensation... 

Both Eu(III) excitation spectroscopy and emission spectroscopy gave information about solution speciation as a function of anion concentration as well as the structure of the bound anions [8]. Carbonate and lactate bound the most weakly = 35 mM, 16 mM, respectively). The lactate and carbonate complexes participate in both innersphere and outersphere interactions as shown by the presence of both the original excitation peak of Eu(STHP)(OH2) and a new red-shifted peak for the innersphere complex (Fig. 8.13a). A non-integral q number of 0.56 for lactate and 0.64 for carbonate is also consistent with a mixture of inner and outersphere complexes. Similarly, acetate, phosphate and methyl phosphate formed a mixture of outersphere and innersphere complexes depending on the conditions of the titrations. Only citrate appeared to form a predominantly innersphere complex with a formation constant of 17 pM (Fig. 8.13b). 

The data assembled in Table 9 allow at least one more interesting conclusion In all instances the formation degree of the macrochelates increases in the order M(AMP)ci < M(IMP)ci < M(GMP)ci. This increase for M(IMP)d < M(GMP)d is in accord with the increased basicity of N7 in GMP compared with that of N7 in IMP [74], However, with AMP the situation is more complicated 9-methylguaninehas ap aOf3.11 i 0.06 [143,144] for its (N7)H site and this value is rather close to the micro acidity constant for the same site in 9-methyladenine, P 1ni = 2.96 0.10 [143]. Hence, the N7 basicity cannot be responsible for the decreased complex stabihty. Similar to the simation with pyrimidine derivatives as discussed in Section 4.2, the reduced stabihty by about 0.5 log unit of Cd(AMP), compared to that of Cd(GMP), is to be attributed to the steric inhibition which (C6)NH2 exercises on a metal ion coordinated at N7 [71]. The (C6)0 group does not have such an effect. In contrast, it rather promotes the stability by forming outersphere bonds to a water molecule of the N7-bound metal ion [74]. 

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