Transition element double oxides

Some Uranium-Transition Element Double Oxides... 

Trialkyl- and triarylarsine sulfides have been prepared by several different methods. The reaction of sulfur with a tertiary arsine, with or without a solvent, gives the sulfides in almost quantitative yields. Another method involves the reaction of hydrogen sulfide with a tertiary arsine oxide, hydroxyhahde, or dihaloarsorane. X-ray diffraction studies of triphenylarsine sulfide [3937-40-4], C gH AsS, show the arsenic to be tetrahedral the arsenic—sulfur bond is a tme double bond (137). Triphenylarsine sulfide and trimethylarsine sulfide [38859-90-4], C H AsS, form a number of coordination compounds with salts of transition elements (138,139). Both trialkyl- and triarylarsine selenides have been reported. The trialkyl compounds have been prepared by refluxing trialkylarsines with selenium powder (140). The preparation of triphenylarsine selenide [65374-39-2], C gH AsSe, from dichlorotriphenylarsorane and hydrogen selenide has been reported (141), but other workers could not dupHcate this work (140). 

Among the transition metals from chromium through zinc, iron remains the only element for which no double oxide formation with uranium oxide has been reported. Both the l.T and 1 3 compounds of mainganese, cobalt, and copper have been prepared, while only the 1 1 compound of chromium, and the 1 3 compound of nickel and zinc are known. 

Hydrothermal experiments with 1 1 mixtures of the transition element oxide and uranium trioxide with a single exception, did not give the desired MUO4 compounds. The CUO-UO3 experiment gave a mixture of CUUO4, CuUsOio, and a basic copper sulfate. All attempts to prepare 1 1 double oxides of the four remaining members of the series led to the formation of the corresponding triuranate phase mixed with unreacted transition element oxide. 

All decomposition reactions are endothermal except that of FeU04, presumably because this is the only reaction which involves oxidation of the double oxide. No significant diflFerence was noted in the DTA or TGA curves of the two NiU04 phases. It is interesting to note the alternating pattern in the decomposition reactions of the uranates. The iron, nickel, and zinc double oxides tend to decompose directly into their constituent oxides, while the manganese, cobalt, and copper compounds decompose to other double oxides. The pattern is not carried over into the decomposition temperatures. In this instance, the thermal stability of the double oxides appears to vary directly with the characteristic transition element oxidation states Gr(III) > Mn, Go (III, II) > Ni, Zn(II) > Gu(II, I). The iron compounds constitute a definite exception to this pattern. 

Somewhat better data are available for the enthalpies of hydration of transition metal ions. Although this enthalpy is measured at (or more properly, extrapolated to) infinite dilution, only six water molecules enter the coordination sphere of the metal ion to form an octahedral aqua complex. The enthalpy of hydration is thus closely related to the enthalpy of formation of the hexaaqua complex. If the values of for the +2 and + 3 ions of the first transition elements (except Sc, which is unstable) are plotted as a function of atomic number, curves much like those in Fig. 11.14 are obtained. If one subtracts the predicted CFSE from the experimental enthalpies, the resulting points lie very nearly on a straight line from Ca " to Zn and from Sc to Fe " (the +3 oxidation state is unstable in water for the remainder of the first transition series). Many thermodynamic data for coordination compounds follow this pattern of a double-humped curve, which can be accounted for by variations in CFSE with d orbital configuration. 

Cerium(IV) forms double salts readily, the best-known one being cerium(IV) ammonium nitrate, CetNOj NH Oj. Although many complex cationic and anionic cerium(IV) species are present in solution, few have been isolated, and these are mostly with anions as ligands. Since the 4f transition elements often form complexes with oxygen compounds, it is possible to prepare Ce(lV) complexes with phosphine oxides or 2,2 -bipyridine 1,1 -dioxide.1-3... 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

Cations of the first transition series do not conform to the smooth pattern for the lanthanide elements shown in fig. 6.1. This is illustrated in fig. 6.2a by the radii of divalent cations in oxides containing transition metal ions in high-spin states. There is an overall decrease of octahedral ionic radius from Ca2+to Zn2+, but values first decrease to V2+, then rise to Mn2+, decrease to Ni2+, and rise again to Zn2+. The characteristic double-humped curve shown in fig. 6.2a has... 

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