Hydroxide complexes nuclearities

Figure 6.31 The structures of (a) dodeca-, (b) pentadeca-, and (c) octadeca-nuclear clusters templated by two IX4-H ions, a X5-X (X = C1, Br) ion, and Xe p r r r r r COj , respectively. Formal assembly of a 60-metal hydroxide complex featuring 26 vertex-sharing [Ln4(ti3-OH)4] cubane units. These cubane building blocks form six dodecanuclear squares and eight octadecanuclear hexagons [102]. (Redrawn from X. Kong et al, A chiral 60-metal sodaUte cage featuring 26 vertex-sharing [Er4(p.3-OH)4] cubanes, Journal of the American Chemical Society, 131, 6918-6919, 2009.)...

Zinc complexes of the cyclen ([12]aneN4 = 1,4,7,10-tetraazacyclododecane) ligand have been extensively studied in terms of phosphate ester hydrolysis reactivity. For example, a proposed binuclear Zn(II) hydroxide complex of cyclen was reported to enhance the rate of hydrolysis of ethyl(2,4-dinitrophenyl)-methylphosphonate and diethyl(2,4-dinitrophenyl) phosphate.223,224 It should be noted that the nuclearity of the zinc-cyclen complex in solution was not conclusively identified in this work. 

Despite all these efforts, the chemistry of molecular lanthanide hydroxides, regardless of the complex nuclearity, has yet to be developed to any significant extent. However, based on the limited number of reports, some general conclusions may already be drawn ... 

All the hydroxide complexes were included in die calculations, but for diese microcrystalline solids with very low solubility products, the concentrations of die species with high nuclearity (such as the (12,4) complex) are so low that they do not appear on this Figure. 

The study has been made in a self-medium , where the ionic medium cation consists of Th". The experiments, potentiometric titrations have been made in test solutions of varying total concentration of protons, Htot, in a -logio[H ] range where the value of is less than 0.1. Hence, the free metal ion concentration is approximately equal to Thtot and it is straightforward to make the necessary corrections for the amount of hydroxide complexes formed. From experiments of this type it is only possible to determine the sum of the concentrations of Th complexes that contain a given number of hydroxide ions (one and two in this study) it is not possible to determine the nuclear-ity of the complexes without additional information. The experimental data obtained refers to reactions of the type... 

Lanthanide Oxide/Hydroxide Complexes of Different Nuclearities... 

Laughlin et al. [122] analysed chloroform extracts of tributyltin dissolved in seawater using nuclear magnetic resonance spectroscopy. It was shown that an equilibrium mixture occurs which contains tributyltin chloride, tributyl tin hydroxide, the aquo complex, and a tributyltin carbonate species. Fluorometry has been used to determine triphenyltin compounds in seawater [123]. Triph-enyltin compounds in water at concentrations of 0.004-2 pmg/1 are readily extracted into toluene and can be determined by spectrofluorometric measurements of the triphenyltin-3-hydroxyflavone complex. 

Foster et al. have developed a method for determining technetium in dissolved nuclear fuel solutions. Tetrapropylammonium pertechnetate is doubly extracted from a basic medium into chloroform and the colored technetium (V) thiocyanate complex is formed in the chloroform phase by the addition of sulfuric acid, potassium thiocyanate and tetrapropylammonium hydroxide. The colored complex absorbs at 513 nm, has a molar extinction coefficient of 46,000 and is stable for several hours. Of more than 50 metals studied, none impairs measurements at ratios less than 100 to 1 mol with respect to technetium. Most anions do not disturb the determination of technetiiun. The standard deviation for a single determination is 0.09 fig over the range of 1 to 20 fig of technetium. 

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