Zirconium complexes polynuclear

A zirconium complex of the wigra-octaethylporphyrinogen ligand reacts with KH to yield a polynuclear hydride. When the reaction is performed in a 1 1 KH Zr ratio, a dinuclear complex is observed. Using a 2 1 KH Zr ratio under rigoronsly controlled reaction conditions leads to the formation of a polynuclear species. In the dinuclear complex, each Zr atom is... 

The metal component of catalysts, solvent selection, and reaction concentration can influence aggregation and affect reactivity. The titanium catalyst 13 forms monomeric complexes in solution, but the analogous zirconium catalyst 14 forms polynuclear aggregates (Figure 9.7) this may explain why the chirality induced by oxidation of the sulfides is opposite for these two catalysts [23]. 

Popov [84POP] studied the complexation of zirconium(lV) by the sulphite ion and postulated the formation of the species Zr(0H)3803 in the pH range 0.54 to 1.44. The formation of this species was premised on the belief that Zr(OH)3 was the dominant species in the pH range studied. It is likely that in this pH range, and for the Zr concentration used in the experiments (0.085 - 1.801 x 10 M), that Zr(OH)( is not the only major Zr hydrolysis species. Further, it is also likely that a mixture of polynuclear and mononuclear species form (see discussion in Appendix D). As such, this review... 

From the study of the literature, it clearly emerged that a considerable number of Zr-carbonate species exist (including polynuclear complexes and ternary carbonato-hydroxo species). The domain of existence of the various species apparently depends on absolute Zr and carbonate concentrations, COa/Zr total concentration ratios and pH. Nevertheless, there is convincing evidence that Zr(C03)4 is the limiting complex when carbonate concentrations are in large excess of zirconium concentrations i.e. COa/Zr ratios above ca. 10). Although the results and the re-interpretations obtained in... 

DAV/ZAB] Davydov, Y. P., Zabrodskii, V. N., Hydrolysis of zirconium(lV) with the formation of mono- and polynuclear hydroxy complexes in solutions, Vestsi Akad. Navuk BSSR, Ser. Khim. Navuk, 2, (1987), 3-8, in Russian. Cited on pages 101, 102, 104, 106, 107,333,404. 

The extremely complicated aqueous solution chemistry of and HP has been reviewed by Larsen, Solovkin and Tsvetkova,and Clearfield. Zirconium(IV) and hafnium(IV) ions undergo extensive hydrolysis, and the predominant solution species are polynuclear, even in dilute (>10 -10 M) solutions of high acidity (1-2 M). Spectrophotometric, " ultracentrifugation, " and light scattering studies point to trinuclear and tetranuclear hydrolysis products complexes such as [M3(OH)4] and [M4(OH)8] have been suggested. ITie mononuclear ions are predominant solution species only at trace metal ion... 

Metallo-silanols also proved to be synthetically valuable in the context of the generation of SiO-bridged polynuclear transition metal complexes [17]. Especially the Et3N-assisted condensation reactions with cyclopentadienyl-titanium and -zirconium chlorides result in nearly quantitative conversions due to the oxophilic nature of the group 4 metals. 

The hexafluoroosmate(IV) anion, [OsFe] ", is extremely inert to aquation. However, aquation of this complex can be catalyzed by zir-conium(IV) rate constants for a range of conditions have been reported. Interestingly and surprisingly, rate constants for zirconium(IV)-catalyzed aquation of [OsFe] , [ReFe] , [PtFe] , and [PFe] are the same under identical conditions. The rate-determining step must therefore involve only the zirconium. Comparison of rate constants for these catalyzed aquations with rate constants obtained in a study of depolymerization of polynuclear zirconium(IV) species in aqueous solution shows that the catalyzed aquation... 

Substitution at polynuclear aqua-ions is often much slower than at the respective parent mononuclear aqua-ions, as has been demonstrated for, e.g., aluminum(III), iron(III), zirconium(IV), and hafnium(IV). A further example has been provided by aluminum, where the Al,3 polynuclear oxo-aqua-species takes several months to equilibrate with lactate. Very different rates of complex formation are used to sort out speciation in multicomponent polynuclear/mononuclear aqua-cation systems. The problems involved in this approach are well illustrated by a Al NMR study of the numerous reaction pathways in the Al " /ferron [ferron = 7-iodo-8-hydroxyquinoline-5-sulfonic acid, (18)] reaction. The slowness of reaction of polynuclear species can cause difficulties in the determination of total metal content, e.g., of aluminum by ferron or Alizarin S (19), in natural waters. In certain situations these... 

---