Uranyl halides

Although thianthrene itself did not form a compound with uranyl halides or nitrate, thianthrene 5-oxide did give yellow solids U02Cl2(T0)2,... 

The uranyl halides UO2X2 are very stable, being salts of the ion... 

Torsional barriers for trimethylphosphine derivatives (63) have been obtained from Raman spectra.56 Vibrational spectra for the uranyl nitrate complex of (63a) have been published.66 Complexes of triarylphosphine derivatives (64) with iodine,67 and of (64b) with metal halides,68 have been the subject of thermodynamic67 and spectroscopic67 68 study. 

In its precipitation reactions ameiicium(IIl) is very similar to the other tripositive actinide elements and to the rare earth elements. Thus the fluonde and the oxalate are insoluble and the phosphate and iodate are only moderately soluble in acid solution, whereas the nitrates, halides, sulfates, sulfides, and perchlorates are all soluble. Americium(VI) can be precipitated with sodium acetate giving crystals isostructural with sodium uranyl acetate,... 

The majority of the devices mentioned thus far rely on the Hofmeister series for anion selectivity. However, for anions that deviate from this series, organometallic receptors can be utilised. The type of ligand or metal centre will influence the sensor selectivity due to the characteristics of the electron acceptance of the complex. An interesting development that is being explored here is the use of calixarenes. These have previously found use as cation-selective species, but with suitable substitution are now being incorporated within anion-selective devices. Compounds suitable as receptors for halides [61],benzoate [61] and acetate [62] have been developed. Reinhoudt and his co-workers have reported the production of a POj-selective CHEMFET based on a uranyl cation immobilised within a salophene ligand (Fig. 5), which shows selectivity over more lipophilic anions such as Br" and NOj [63]. 

The quenching of uranyl luminescence by halide ions in solutions has been investigated by many workers2,201 202). Quantitative results reported in recent papers have been collected in Table 6. The quenching constant decreases in the order... 

The majority of U(VI) coordination chemistry has been explored with the trans-dioxo uranyl cation, U02+2. The simplest complexes are ammonia adducts, of importance because of the ease of their synthesis and their versatility as starting materials for other complexes. In addition to ammonia, many of the ligand types mentioned in the introduction have been complexed with U(VI) and usually have coordination numbers of either 6 or 8. As a result of these coordination environments a majority of the complexes have an octahedral or hexagonal bipyramidal coordination environment. Examples include U02X2Lw (X = halide, OR, N03, RC02, L = NH3, primary, secondary, and tertiary amines, py, n = 2-4), U02(N03)2Lk (L = en, diaminobenzene n = 1, 2). The use of thiocyanates has lead to the isolation of typically 6 or 8 coordinate neutral and anionic species, ie, [U02(NCS)J2 xj H20 (x = 2-5). 

Other uranyl salts are given by organic acids,41 sulfate, halides, and so on the water-soluble acetate in the presence of an excess of sodium acetate in dilute acetic acid gives a crystalline precipitate of NaU02(0C0CH3)3. There is considerable research on the use of cyclic hexadentate and related ligands to form strong complexes with the U02+ ion. 

The best-studied aqueous actinide halide systems are the fluorides and the chlorides. Fluoride and chloride ions are added to the actinyl centers in a stepwise fashion (Scheme 4). The end member in the actinyl fluoride system is the pentafluoride, An02F5 . For the uranyl analog, the U = O and U-F bond distances were found to be 1.79 and 2.18A respectively. The uranium tetrafluoride ion, U02F4 , has been isolated as a dimer with two bridging fluoride ligands. The U = O, U-Fterminai, uud U-Fbridging distauces for this complex were found to be 1.79, 2.15 to 2.20 A, and 2.30 A, respectively. 

Hexavalent. The majority of An(VI) coordination chemistry with N-donors has been explored with the uranyl cation, 50i. Stable adducts with the hgands discussed in the tri- and tetravalent complexes have been described, for example, U02X2L (X = halide, OR, NO3, RCO2). The coordination numbers observed for these complexes are typically 6, 7, or 8 with octahedral, pentagonal bipyramidal, or hexagonal bipyramidal geometries, respectively. Neutral and anionic thiocyanates have also been isolated, for example [U02(NCS)j2- yH20(x = 2 5). 

For example, halide ions may form soluble actinide complexes without addition of nitric acid vapor. Preliminary tests have shown, however, that uranyl chloride, UO2CI2, is not soluble in either a 6-mole% potassium chioride/94-mole% potassium nitrate melt, or a 5-mole% sodium chloride/95-mole% sodium nitrate melt. Uranyl fluoride, UO2F2, was slightly soluble in a 9-mole% potassium fluoride/91-mole% potassium nitrate system. There was no evidence of solubility of uranyl fluoride in 3.5 mole% sodium fluoride/96.5-mole% sodium nitrate. 

The structures of the metal, hydrides, and carbides are described in other chapters, as also are the halides MX3, MX4, and MX5. Here we devote sections to certain halide structures peculiar to U, complex fluorides of Th and U, oxides of U, uranyl compounds and uranates, nitrides and related compounds, and conclude with a note on the sulphides of U, Th, and Ce. 

The rate constants in quenching reactions of uranyl luminescence by halide ions... 

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