Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Coordination stability constants

Compared to later elements in their respective transition series, scandium, yttrium and lanthanum have rather poorly developed coordination chemistries and form weaker coordinate bonds, lanthanum generally being even less inclined to form strong coordinate bonds than scandium. This is reflected in the stability constants of a number of relevant 1 1 metal-edta complexes ... [Pg.950]

In the introductory chapter we stated that the formation of chemical compounds with the metal ion in a variety of formal oxidation states is a characteristic of transition metals. We also saw in Chapter 8 how we may quantify the thermodynamic stability of a coordination compound in terms of the stability constant K. It is convenient to be able to assess the relative ease by which a metal is transformed from one oxidation state to another, and you will recall that the standard electrode potential, E , is a convenient measure of this. Remember that the standard free energy change for a reaction, AG , is related both to the equilibrium constant (Eq. 9.1)... [Pg.176]

Treichel, Knebel, and Hess provided further data on these systems by studying reactions of [Pt(PRj)2(CNCH3)2] with various halide ions and with pseudohalides. A series of five-coordinate complexes were obtained from reactions with iodide ion (PRj = PPhj, PPh2Me, PPhMe2, PEtj), and a study was carried out to measure the stability of these complexes with respect to ligand loss 155). Stability constants for several of these complexes were obtained from spectroscopic data. Other reactants (Cl, Br, CN, SCN) generally yielded the appropriate [Pt(PRj)2(CNCH3)X] species, as expected. [Pg.78]

The coupling reaction of 1 (M=Zn) affords CPO 3 (M=Zn) in 55% yield in the presence of template 2 however, the absence of 2 decreases the yield to 34% [22]. With the increase of yield of 3, template 2 induces the selectivity of the reaction the yield of the by-product (cychc dimer 4 (M=Zn)) was changed from 23% (with no template) to 6% (in the presence of template). A similar CPO formation reaction was reported for the corresponding ruthenium porphyrins (3, M=Ru(CO)), in which the stability constant of the Ru-N coordination bond is 10 larger than that of the Zn-N coordination bond [23]. Although the transition state of the CPO produced by the ruthenium-based substrate is expected to be more stable than that produced by ZnPor, the yield of 3 (M=Ru(CO)) is only... [Pg.73]

Regular pyrimidines are less effective ligands for Ni11 ions. They may use, inter alia, their C=0 donor to yield monodentate coordination.1835 Insertion of a sulfur atom into a pyrimidine moiety increases considerably its binding ability.1836 Thiolation of uridine at C(2) or C(4) results in formation of a quite effective S,N3 four-membered chelate in the complexes with Ni11. Thiolation of purine at C(6) increases the stability constant by 3.5 orders of magnitude. [Pg.421]

In the case of macrocyclic tacn side arms, stability constants of type (820) dinickel complexes are considerably higher and six-coordination can be achieved due to the binding of additional coligands, either at both Ni11 (in (828))2031 or at only one of them (in (829)).2082... [Pg.451]

Open chain polyamine ligands have been widely studied. Often the coordination of zinc is compared with other first row transition metals and factors, such as behavior across a pH range, studied. The protonation patterns and stability constants are of particular interest. Octahedral zinc tris(ethylenediamine) structures have been characterized by X-ray diffraction with a number of different counter anions.94 The X-ray structure of zinc tris(ethylenediamine) with fluoride counter ions reveals extensive hydrogen bonding.95... [Pg.1153]

The ligand 6,13-dimethyl-l,4,8,ll-tetra-azacyclotetradecane-6,13-diamine coordinates as a hexadentate ligand to zinc in neutral aqueous solution. Potentiometric titrations were used to determine the stability constant for formation. The pXa values were determined for five of the six possible protonation steps of the hexamine (2.9, 5.5, 6.3, 9.9 and 11.0).697 Studies of the syn and anti isomers of 6,13-dimethyl-1,4,8, ll-tetraazacyclotetradecane-6,13-diamine reveal that they offer different shapes for metal binding, which is reflected in the stability constants for 1 1 zinc ligand ratio complexes. The selectivity of binding to the zinc ion compared to the cadmium(II) ion by both isomers is significant.698... [Pg.1207]

The stability constants of zinc complexes of 4,6-dimethyl-2-thiopyrimidine have been determined by potentiometric measurements. The crystal structure shows infinite zigzag chains of ZnL2 units with each zinc coordinated by an N3S2 donor set in a trigonal-bipyramidal geometry.853... [Pg.1222]

Mapsi et al. [16] reported the use of a potentiometric method for the determination of the stability constants of miconazole complexes with iron(II), iron(III), cobalt(II), nickel(II), copper(II), and zinc(II) ions. The interaction of miconazole with the ions was determined potentiometrically in methanol-water (90 10) at an ionic force of 0.16 and at 20 °C. The coordination number of iron, cobalt, and nickel was 6 copper and zinc show a coordination number of 4. The values of the respected log jSn of these complexes were calculated by an improved Scatchard (1949) method and they are in agreement with the Irving-Williams (1953) series of Fe2+ < Co2+ < Ni2 < Cu2+ < Zn2+. [Pg.38]

The above account of selectivity of inorganic plus organic chemistry in synthesis is given rather extensively to stress three points. All the four (Mg, Fe, Co and Ni) porphyrin products came from one source, the synthesis of uroporphyrin. The basis of selection is very different from that in primitive centres which use thermodynamic stability constant selectivity based on different donor atoms for different metal ions. Here, all ion complexes have the same donor atoms, nitrogen, the most constrained being the coordination of Mg2+ by five nitrogens exactly as is seen for Fe in haemoglobin. Hence, there also has to be a new control feedback to ensure that the appropriate quantities of each metal cofactor is produced in a balanced way, that is synthesis from uroporphyrin has to be divided based upon... [Pg.217]

Ar,A,-bis(2-hydroxybenzyl)-ethylenediamine-A,A, -diacetic acid (HBED) and IV-hydroxybenzyl-ethylenediam i ne- A-, A", N -iri acetic acid (HBET) are multidentate ligands investigated for coordination with gallium and indium (Figure l).78 HBED, with its two phenolate donor groups, led to increased stability constants over HBET. [Pg.892]

We shall ignore for the moment the fact that the solvent plays a role and will represent the formation of the successive complexes as shown in Eqs. (19.17) to (19.19). However, we should not lose sight of the fact that in aqueous solutions, the total coordination number of the metal is m, and if x sites are bonded to water molecules and y sites are where ligands are attached, then x + y = m. Because the constants Ku I<2,..., Km represent the formation of complexes, they are called formation constants. The larger the value of a formation constant, the more stable the complex. Consequendy, these constants are usually called stability constants. [Pg.676]

We now have a sufficient number of conditions to determine the relationship between the measured equilibrium constants, K), K2,-, Km, and the statistically corrected constants, K), K2, ..., Km. The statistical corrections to be applied to the experimental stability constants are shown in Table 19.1 for the most common coordination numbers. [Pg.680]

Electrochemical experiments allow the determination of complex stability constants for Fe2+ by measuring complex redox potentials over a range of pH values. The Fe34YFe2+ redox potential of the siderophore complex, as with the spectral characteristics of the complex, is dependent on the inner coordination environment of the iron. These considerations will be addressed later (Section III.D). [Pg.194]


See other pages where Coordination stability constants is mentioned: [Pg.2013]    [Pg.2013]    [Pg.1170]    [Pg.1191]    [Pg.242]    [Pg.19]    [Pg.384]    [Pg.257]    [Pg.69]    [Pg.23]    [Pg.15]    [Pg.121]    [Pg.289]    [Pg.289]    [Pg.319]    [Pg.373]    [Pg.404]    [Pg.411]    [Pg.748]    [Pg.973]    [Pg.1153]    [Pg.1209]    [Pg.1210]    [Pg.1212]    [Pg.1219]    [Pg.856]    [Pg.6]    [Pg.20]    [Pg.679]    [Pg.680]    [Pg.70]    [Pg.94]    [Pg.187]    [Pg.191]    [Pg.193]   


SEARCH



Coordination complexes stability constant

Stability constants

Stability constants of coordination complexes

Stability constants of coordination compound

© 2024 chempedia.info