Protactinium complexes

Propionohydroxamic acid metal complexes, 506 Propylenediamine metal complexes, 34 Protactinium complexes cupferron, 510 Proteins... 

Unit cell dimensions for the tetravalent protactinium fluoro complexes are listed in Table VIII. LiPaFs is a member of an isostructural series of 1 1 complexes formed by the actinide elements thorium to curium inclusive (91). Structural details are available for LiUP5 (5S), but bond distances have not been reported for the protactinium complex. The 7 6 complexes, like their actinide(IV) analogs (Th-Cm with Na, Th-Cm with K, and Th-Pu with Rb) are all 4, 114) isostructural with Na7Zr F3 (60) in which each zirconium atom is 8-coordinate and the... 

Propionohydroxamic acid metal complexes, 506 Propylenediamine metal complexes, 34 Protactinium complexes cupferron, 510 Proteins electron transfer active sites, 525 metal complexes, 759-774 binding sites, 769,771 naturally occurring, 974 occurrence, 962 Proton exchange amine ligands, 24 Protonolysis metal alkoxides, 352 Prussian blue, 7, 8 Pseudocubanes structure... 

The extensive hydrolysis of protactinium in its V oxidation state makes the chemical investigation of protactinium extremely difficult. Ions of protactinium(V) must be held in solution as complexes, eg, with fluoride ion, to prevent hydrolysis. 

Protactinium is separated by solvent extraction and anion exchange processes by using sulfate solutions. After chemical separation, the protactinium salts are ignited to a pentoxide, Pa205, which may be converted into an arsenazo(III) complex. The absorbance of the solution is measured at 630 nm with a spectrophotometer. Protactinium-231 is an alpha emitter and also forms photons at 300 KeV, which can be measured by various radioactive counters and spectrophotometric techniques. Protactinium also can be measured by neutron activation analysis. 

Bromofluorobenzene, formation by nuclear activation, 5 191-192 Bromofluorophosphine, 13 378-380 Bromopiotactinates, see Protactinium, bromo complexes of... 

Dimesitylazidoborane, preparation, 9 137 Dimethliodosulfonium slats, 35 262 Dimethylacetamide complexes with protactinium, 12 31, 32... 

Protactinium (continued) pentachloride, 12 10, II complexes with phosphine oxides, 12 30, 31... 

Thorium(III) and protactinium(III) complexes are unknown, and relatively few uranium(III), neptunium(III) and plutonium(III) compounds have been described. This is mainly because of the ease of oxidation to the +4 state in all three cases, accentuated for plutonium(III) by the oxidizing nature of the a-radiolysis products formed in solutions. 

Because of the ease of oxidation of protactinium(IV) and uranium(IV), peroxides and peroxo complexes are limited to their higher oxidation states. The compounds M04"JcH20 precipitated from dilute acid solutions of neptunium(IV) and plutonium(IV) by hydrogen peroxide appear to be actinide(IV) compounds. Soluble intermediates of the type [Pu( U-02)2Pu]4+ are formed at low hydrogen peroxide concentrations. 

Th(PhCOCHCOPh)4 has been reported as being isomorphous with the corresponding protactinium(IV), uraniumflV) and cerium(IV) complexes the coordination geometry in the last is a triangular faced dodecahedron, but a more recent publication73 reports the coordination geometry of the uranium(IV) compound as square antiprismatic. 

The only recorded complexes appear to be the protactinium(V) compounds, Pa(Et2NCS2)4X (X = Cl, Br), prepared by treating a suspension of the pentahalide in dichloromethane with an excess of Na(Et2NCS2), followed by vacuum evaporation of the filtrate. 

The protactinium(V) complexes of composition PaXsL (X = Cl, Br R = Ph3PS, (Ph2PS)2CH2) have been recorded. 

A few salts of composition (Et4N)2[MvOX5] (Mv = Pa, X = C1, Br MV = U, X = F) are known the uranium(V) compound is obtained from the dihydrate under vacuum, and the protactinium(V) chlorocompound is prepared by hydrolysis of the hexachloro complex salt in methyl cyanide containing 0.5% water. Salts of composition (Et4N)[Pa(OEt)2X4j (X = Cl, Br) are also known. 

The predominant oxidation stale of the element is (V). There is some evidence that the (IV) state is obtained under certain reduction conditions. When the pentapositive form is not in the form of a complex ion it may exist in solution as PaC>2+. The compounds are very readily hydrolyzed in aqueous solution yielding aggregates of colloidal dimensions, thus showing marked similarity to niobium and tantalum in this respect. These properties play a dominant role in the chemical properties of aqueous solution, because the element is so easily removed from solution by hydrolysis and adsorption Protactinium coprecipilates with a wide variety of substances, and it seems likely that the explanation for this lies in the hydrolytic and adsorptive behavior. 

The element is difficult to maintain in aqueous solution in the form of simple salts. Solubility data seem to indicate that such amounts as can be dissolved probably do so entirely by formation of complex ions. Fluoride ion strongly complexes protactinium, and it is due to this that protactinium compounds are in general soluble in hydrofluoric acid. 

Protactinium can be separated from natural ore concentrates by cycles consisting of adsorption on Mn02 precipitates followed by solvent extraction of the cupferron complex with pentyl acetate.94... 

HEXAHALOGENO SALTS AND ALKYL NITRILE COMPLEXES OF TITANIUM(IV), ZIRCONIUM(IV), NIOBIUM(V), TANTALUM(V), PROTACTINIUM (IV) AND -(V), THORIUM(IV), AND URANIUM(IV)... 

Niobium and tantalum(V) chlorides and tantalum(V) bro-midef yield the complexes MX6-CHSCN, and protactinium(V) bromide yields orange PaBr8 3CH8CN if the same procedure is used. 

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