Aminopolycarboxylate complexes

The existence of a wide variety of zirconium(IV)-aminopolycarboxylate complexes in solution was established by the potentiometric titration studies of Intorre and Martell.675-677 This work and related solution studies have been reviewed by Larsen.5 Zirconium(IV) forms 1 1 and 1 2 complexes with tetradentate aminopolycarboxylates, 1 1 complexes with hexadentate and octadentate aminopolycarboxylates, and mixed ligand complexes with aminopolycarboxylates and various bidentate ligands, for example 1 1 1 Zr-edta-Tiron and 1 1 2 Zr—nta-Tiron complexes (Tiron = l,2-dihydroxybenzene-3,5-disulfonate). The stoichiometries of these complexes are consistent with the tendency of zirconium to achieve a coordination number of eight. 

Kinetics of Water Exchange on Aminopolycarboxylate Complexes of Mn11, Fe11, Fe ", or Niu... 

The reduction potential of 0.2 V for Reaction (4) at pH 7 depends very much on the reduction potential of the Fe(III)/Fe(II) couple, Reaction (3). The 0.1V assumed here for that half-reaction is close to that of various iron-aminopolycarboxylate complexes. The uncertainty in our reduction potential for Reaction (4) is estimated at 0.2 V The abstraction of a doubly allylic hydrogen is estimated to require a reduction potential of 0.6 V (see Table 1),... 

If we use this rate constant to calculate the water exchange rate following the derivation used for the T1(EDTA) -X system, we obtain = k(IK s = 1.3 10 s K a = 0.012 M ). This value is close to the water exchange rate for the Eu q ion (296). It is possible that Tl(EDTA)aq" behaves similarly to rare-earth aminopolycarboxylate complexes, in which some water molecules can also be coordinated to the metal ion. 

Proton relaxation NMR using Gd(IH) support these conclusions. Spin-lattice relaxation (Ti) values are inversely related to the average number of inner sphere hydration waters of the lanthanide cation (50-52). Chang reported hydration values of 3 and 1 for Gd complexes of EDTA and DTPA, respectively. Both NMR relaxation studies and luminescence lifetime data indicate a total coordination number between 8 and 10 for the lanthanides in aminopolycarboxylate complexes. 

Thermodynamic studies of lanthanide-aminopolycarboxylate complexation have been quite valuable in the understanding of lantiianide coordination chemistry. The same experimental conditions of Grenthe (42,43) were utilized by Choppin,... 

The exchange of a radioisotopic lanthanide for a stable lanthanide metal chelated to an aminopolycarboxylate ligand has been found to proceed via two mechanistic pathways(tiO). Below pH 6, an acid-catalyzed mechanism predominates in which protonation catalyzes decomposition of die lanthanide-aminopolycarboxylate complex. The uncomplexed ligand chelates with free lanthanide cations in solution. The mechanism below illustrates the acid-catalyzed pathway, where A = aminopolycarboxylate ligand (t denotes the activated complex Ln is die radioactive tracer). 

Conventional d.c. polarography and n.m.r. spectroscopy have been used to measure the rates of dissociation of several aminopolycarboxylate complexes of lead(u). 

Enthalpies and entropies of activation have been measured in the oxidation of manganese(II)-aminopolycarboxylate complexes by Br2 and An... 

Hamm, R.E. Suwyn, M.A. "Preparation and characterization of some aminopolycarboxylate complexes of manganese(III)", Inorg. Chem. 1967, 6, 139-145. 

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