Actinium species

In 1899, Andre Debierne added ammonium hydroxide to a solution of the U mineral pitchblende. When the lanthanoids precipitated as the hydroxides, a radioactive species was carried along. This element, which was a product of the radioactive decay of U-235 was named actinium. The species was Ac-227 (half life 21.77 years)... 

Ac, actinium, was initially identified in 1899 by Andr6-Louis Debierne, a French chemist, who separated it from pitchblende. He dissolved the mineral in acid, then added NH4OH, and found that a radioactive species was carried down with the rare earth hydroxides. He named the element actinium after the Greek aktinos which means ray. Because of its low abundance in U, the element is usually not obtained by isolation from U. It can be obtained in mlligram amounts by irradiation of Ra-226 in a nuclear reactor. The preparation of Ac metal involves reduction of AcFs by Li at high temperature. 

A radioactive element is an element that disintegrates spontaneously with the emission of various rays and particles. Most commonly, the term denotes radioactive elements such as radium, radon (emanation), thorium, promethium, uranium, which occupy a definite place in the periodic table because of their atomic number. The term radioactive element is also applied to the various other nuclear species, (which arc produced by the disintegration of radium, uranium, etc.) including (he members of the uranium, actinium, thorium, and neptunium families of radioactive elements, which differ markedly in their stability, and are isotopes of elements from thallium (atomic number 81) to uranium (atomic number... 

A tiny amount of a very unstable species (half-life, 21 minutes) has been detected among the decay products of actinium tracer experiments by Mile. M. Perey showed that this species has the same chemistry as that of cesium and is presumably the heaviest alkali metal. It is named francium after Mile. Perey s homeland. 

The formation constants of an actinium isopropyltropolonate complex were determined. Thermochemically relevant studies of thorium enolates generally involve bis(pentamethyl-cyclopentadienyl)thorium derivatives. Cp 2Th(Cl)(C(0)CFl2Bu-f) with an anionic acyl group that readily rearranges to the isomeric enolate Cp 2Th(Cl)OCH=CHBu-t. The Z-isomer is formed upon heating and the -isomer upon catalysis with Cp 2ThH2. Is the E or Z enolate thermodynamically more stable For the simple alkyl enolates MeCH=CHOR, the equilibration reaction of the Z- and E-isomers is nearly thermo-neutral . Consider the two species Cp 2Th(H)OCH(Bu-t)2 and Cp 2Th(H)0-2,6-C6H3 (Bu-f)2. The reversible addition of CO yields the rp- formyl derivative in reactions that are 19 4 and 25 6 kJmoR exothermic. These formyl species dimerize to form the classical enediolate, Cp 2Th(OR)OCH=CHO(OR)ThCp 2. This product is formed as the Z-isomer, plausibly thermodynamically preferred over the -isomer, much as (Z)-MeOCH=CHOMe is preferred over its E-counterpart by 6.0 0.2 kJmoR. ... 

The terrestrial occurrence of Ac, Pa, U, and Th is due to the half-lives of the isotopes 235U, 238U and 232Th which are sufficiently long to have enabled the species to persist since genesis. They are the sources of actinium and protactinium formed in the decay series and found in uranium and thorium ores. The half-lives of the most stable isotopes of the trans-uranium elements are such that any primordial amounts of these elements appear to have disappeared long ago. However, neptunium and plutonium have been isolated in traces from uranium13 minerals in which they are formed continuously by neutron reactions such as... 

The conventional spectrosct k notation fcx- zero-valent actinium is Ac L Similarly, the singly ionized species is Ac II, and the doubly charged, Ac ID. The chemkal notation for the latter is Ac Ac(u). I en referring to free-ion spectra we will use the spectroscopic notation. When indicating the valence state of an ionic species in a condensed phase we will use the chemical notation. We use the symbol An to represent any actinide element, Ln as the general symbol for the lanthanides. 

Selected values of actinide aquo-ion enthalpies of formation of actinium through berkelium (except for any Pu(vii) species) were assessed by Fuger and Getting [15] their values have been adopted here in Tables 17.1 and 17.14. For berkelium and californium, new measurements have provided the tabulated enthalpies of formation. All An values are plotted in Fig. 17.1. For heavier actinides, Nugent et al. [29] estimated enthalpies of formation systematically David et al. [25,27] applied more elaborate systematics and electrochemical measurements to estimate aquo-ion enthalpies of formation. David s predictions for and AHf(Cf ) have been borne out by experiments. Some... 

All isotopes of actinium are radioactive and exist in aqueous solution only in the trivalent state. All of the isotopes of actinium are relatively short lived, with the longest half-life being 21.6 years for Ac. Consequently, it is difficult to measure the stability of its aqueous species or the solubility of its phases. 

The chemical behaviour of actinium will be similar to that of lanthanum. Data are only available for two monomeric hydrolysis species and the solubility of the hydroxide phase. The solubility of this phase can be described by reaction (2.13) (M = Ac, x = 0), whereas the hydrolysis constants can be described by reaction (2.5) (M = = 1) for actinium(lll) in reaction (2.5),, the number of hydrox-... 

The thermodynamic parameters for actinium(lll) hydrolysis species and hydroxide phases are listed in Table 9.1. These data have been calculated using the constants accepted in this work and thermodynamic data for Ac(s) and Ac given by Bard, Parsons and Jordan (1985). These latter authors also give thermodynamic data for Ac(OH)3(s), their Gibbs energy value being in excellent agreement with that derived in the present review. 

Table 9.1 Thermodynamic data for actinium(lll) species at 25 °C determined in the present review and those given in the literature for Ac(s) and Ac +.

There are no data reported in the literature that give reliable stability or solubility constants for the hydrolytic species of uranium(III) derived from experimental studies. Savenko (1998) estimated a stability constant for U(OH)3(aq) from a solubility constant provided in the literature for U(OH)3(s) (Lure, 1989). The reported solubility constant was log = 3.0, which led to a stability constant for U(OH)j(aq) of log = -32.6. There is no confirmatory evidence for these constants, and, as such, they are not retained. Moreover, given the smaller ionic radius of uranium(III) compared to that of actinium(III) (Shannon, 1976), the former ion should have a more positive log 3 and a more negative log which is not the case, providing support for the rejection of the data for uranium(III). 

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