Mixed --complexes

In TBP extraction, the yeUowcake is dissolved ia nitric acid and extracted with tributyl phosphate ia a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N02)2(TBP)2 which is extracted iato the diluent. The purified uranium is then back-extracted iato nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N02)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated duting a pyrolysis step to form uranium trioxide [1344-58-7], UO, as shown ia equation 10. The pyrolysis is most often carried out ia either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The UO is reduced with hydrogen to uranium dioxide [1344-57-6], UO2 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF, with HF at elevated temperatures (eq. 12). The UF can be either reduced to uranium metal or fluotinated to uranium hexafluoride [7783-81-5], UF, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to UO, UO2, and ultimately UF have been discussed ia detail (40). 

Complexes (191) and (192) are formed from dimethyldiazirine with carbonyls of chromium, molybdenum and tungsten. They show no tendency towards N—N cleavage (80JOM(193)57). Complex (193) is made from a mixed complex by displacement of norbor-nadiene. 

Mixed complexes in which a metal is coordinated by a dithiolene and by other ligands such as CO, NO, R3P, etc., are also known. 

Mixed complexes [Ru(bipy)2L](C104)2 (L = phen, 5-methyl(phen)) have virtually identical Ru-N (phen) and Ru-N (bipy) distances. 

In addition to the methods already outlined for platinum(II) complexes, simultaneous crystallization can be used to prepare mixed complex halides (Figure 3.105). 

A similar mixed complex with Mn and Co is obtained by reacting the triple-decked cobalt compound XVII with hlnjCCO), ... 

Homoleptic complexes have been obtained also with tetrakis(l-pyrazolyl)borates, e.g., [ B(pz)4 2Cd] and [ B(3-Mepz)4 2Cd] (both P2 jc, Z = 2) in both compounds structure analyses the ligands have been shown to coordinate trihapto, i.e., with one pz ring free. In both cases Cd has a distorted octahedral environment, with averaged structural data very similar to those for the tris(l-pyrazolylhydridoborate complexes.201 Variable-temperature 3H NMR studies of these and of mixed complexes with tris- and bis(l-pyrazolylhydridoborates indicate fluxional behavior (coalescence temperatures and barriers for the dynamic processes are given). 

From the point of view of complex formation, homogeneity of mixed oxides accessible by means of Pechini-type routines could be a result of the emergence of mixed complex compounds where two different cations are bonded to one and the same anion. Such a conjecture formulated in Ref. [7] yet has no definite proofs, and no attempts have been made in order to quantify the very role of complex formation in Pechini-type syntheses. 

In order to co clarify the role of complex formation, the new data on stability constants should be accumulated, being collected at strictly similar conditions. It should be also mentioned that any analysis of equilibrium in solutions involving anions of polybasic hydroxy carboxylic acids requires the data on the deprotonation constants of the acid in question. This information would be crucial for conclusions regarding the presence and stability of mixed complexes in the system. Valuable knowledge about the structure of complex compounds present in solutions (and in precursors as well, see later) may be gained by means of vibrational spectroscopy (IR and Raman spectra) and nuclear magnetic resonance. 

Two complexes (RNOA11CI3 with R = Ph,/>-Tol have been reported in the older literature.199 The compounds were obtained as yellow solids from the reaction of HAuC14 with the isocyanides in ethanol. Mixed complexes of the type (RNG)AuXn(C6F5)3 n with certain combinations of n = 0-3, X = C1, Br, I, and R = cBu, Cy, Ph,/>-Tol have also been documented from earlier work. 

Another distinct property of mixed complexes which we mention here is the possibility to observe two activation regimes of relaxation of magnetization. One of them corresponds to reversal of magnetization of individual ions, at higher temperatures, and the other is related to climbing over the barrier built from the exchange multiplets of the complex. The coexistence of these two relaxation regimes has been recently revealed in the Co Dy ,11 complex in a combined study... 

Bis(benzene)chromium(0) is easily oxidized, and mixed complexes are obtained by means of substitution reactions. For example,... 

Survival of the ions is assisted by the solvent. Complexes with bridging tin atoms, and mixed complexes, are particularly interesting. Oxidation of the latter is followed by cleavage of either of the tin-metal bonds as in the following example ... 

The two related complexes [Li4 2-As(SiMe3)2 2 3-As(SiMe3)2 2 (THF)2] (37) and [Li As(SiMe3)2 (THF)2]2 have been isolated and structurally characterized (103). The former complex was isolated in very low yield from the reaction of LiAs(SiMe3)2 with InCl3 after recrystallization from pentane, whereas the latter complex was isolated by recrystallization of LiAs(SiMe3)2 from a pentane/THF mix. Complex 37 is isostructural with its phosphorus analogue 7 (vide supra) and con-... 

The disubstituted acetonitrile complex has been found to undergo all the reactions cited above for the cyclooctene complex. A particular advantage of these compounds is that it is possible sequentially to replace the ligands to produce the intermediate compound [Os3(CO)10-(CN3CN)X], which may then be further reacted to give a mixed complex [Os3(CO)10XX ]. 

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