Astatine compounds

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Astatine compounds are compounds that contain the element astatine (At). As this element is very radioactive, few compounds have been studied. Less reactive than iodine, astatine is the least reactive of the halogens. [1] Its compounds have been synthesized in nano-scale amounts and studied as intensively as possible before their radioactive disintegration. The reactions involved have been typically tested with dilute solutions of astatine mixed with larger amounts of iodine. Acting as a carrier, the iodine ensures there is sufficient material for laboratory techniques (such as filtration and precipitation) to work. [2] [3] [lower-alpha 1] Like iodine, astatine has been shown to adopt odd-numbered oxidation states ranging from −1 to +7.

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Only a few compounds with metals have been reported, in the form of astatides of sodium, [6] palladium, silver, thallium, and lead. [7] Some characteristic properties of silver and sodium astatide, and the other hypothetical alkali and alkaline earth astatides, have been estimated by extrapolation from other metal halides. [8]

Hydrogen astatide space-filling model Hydrogen-astatide-calculated-3D-sf.svg
Hydrogen astatide space-filling model

The formation of an astatine compound with hydrogen – usually referred to as hydrogen astatide – was noted by the pioneers of astatine chemistry. [9] As mentioned, there are grounds for instead referring to this compound as astatine hydride. It is easily oxidized; acidification by dilute nitric acid gives the At0 or At+ forms, and the subsequent addition of silver(I) may only partially, at best, precipitate astatine as silver(I) astatide (AgAt). Iodine, in contrast, is not oxidized, and precipitates readily as silver(I) iodide. [10] [11]

Astatine is known to bind to boron, [12] carbon, and nitrogen. [13] Various boron cage compounds have been prepared with At–B bonds, these being more stable than At–C bonds. [14] Astatine can replace a hydrogen atom in benzene to form astatobenzene C6H5At; this may be oxidized to C6H5AtCl2 by chlorine. By treating this compound with an alkaline solution of hypochlorite, C6H5AtO2 can be produced. [15] The dipyridine-astatine(I) cation, [At(C5H5N)2]+, forms ionic compounds with perchlorate [13] (a non-coordinating anion [16] ) and with nitrate, [At(C5H5N)2]NO3. [13] This cation exists as a coordination complex in which two dative covalent bonds separately link the astatine(I) centre with each of the pyridine rings via their nitrogen atoms. [13]

With oxygen, there is evidence of the species AtO− and AtO+ in aqueous solution, formed by the reaction of astatine with an oxidant such as elemental bromine or (in the last case) by sodium persulfate in a solution of perchloric acid: [10] [17] the latter species might also be protonated astatous acid, H
2AtO+
2. [18] The species previously thought to be AtO−
2 has since been determined to be AtO(OH)−
2, a hydrolysis product of AtO+ (another such hydrolysis product being AtOOH). [19] The well characterized AtO−
3 anion can be obtained by, for example, the oxidation of astatine with potassium hypochlorite in a solution of potassium hydroxide. [15] [20] Preparation of lanthanum triastatate La(AtO3)3, following the oxidation of astatine by a hot Na2S2O8 solution, has been reported. [21] Further oxidation of AtO−
3, such as by xenon difluoride (in a hot alkaline solution) or periodate (in a neutral or alkaline solution), yields the perastatate ion AtO−
4; this is only stable in neutral or alkaline solutions. [22] Astatine is also thought to be capable of forming cations in salts with oxyanions such as iodate or dichromate; this is based on the observation that, in acidic solutions, monovalent or intermediate positive states of astatine coprecipitate with the insoluble salts of metal cations such as silver(I) iodate or thallium(I) dichromate. [15] [23]

Astatine may form bonds to the other chalcogens; these include S7At+ and At(CSN)−
2 with sulfur, a coordination selenourea compound with selenium, and an astatine–tellurium colloid with tellurium. [24]

Structure of astatine monoiodide, one of the astatine interhalogens and the heaviest known diatomic interhalogen. Astatine-iodide-3D-vdW.svg
Structure of astatine monoiodide, one of the astatine interhalogens and the heaviest known diatomic interhalogen.

Astatine is known to react with its lighter homologs iodine, bromine, and chlorine in the vapor state; these reactions produce diatomic interhalogen compounds with formulas AtI, AtBr, and AtCl. [4] The first two compounds may also be produced in water – astatine reacts with iodine/iodide solution to form AtI, whereas AtBr requires (aside from astatine) an iodine/iodine monobromide/bromide solution. The excess of iodides or bromides may lead to AtBr−
2 and AtI−
2 ions, [4] or in a chloride solution, they may produce species like AtCl−
2 or AtBrCl−
 via equilibrium reactions with the chlorides. [5] Oxidation of the element with dichromate (in nitric acid solution) showed that adding chloride turned the astatine into a molecule likely to be either AtCl or AtOCl. Similarly, AtOCl−
2 or AtCl−
2 may be produced. [4] The polyhalides PdAtI2, CsAtI2, TlAtI2, [25] [26] [27] and PbAtI [28] are known or presumed to have been precipitated. In a plasma ion source mass spectrometer, the ions [AtI]+, [AtBr]+, and [AtCl]+ have been formed by introducing lighter halogen vapors into a helium-filled cell containing astatine, supporting the existence of stable neutral molecules in the plasma ion state. [4] No astatine fluorides have been discovered yet. Their absence has been speculatively attributed to the extreme reactivity of such compounds, including the reaction of an initially formed fluoride with the walls of the glass container to form a non-volatile product. [lower-alpha 2] Thus, although the synthesis of an astatine fluoride is thought to be possible, it may require a liquid halogen fluoride solvent, as has already been used for the characterization of radon fluoride. [4] [22]

Notes

  1. ↑ Iodine can act as a carrier despite it reacting with astatine in water because these reactions require iodide (I−), not (only) I2. [4] [5]
  2. ↑ An initial attempt to fluoridate astatine using chlorine trifluoride resulted in formation of a product which became stuck to the glass. Chlorine monofluoride, chlorine, and tetrafluorosilane were formed. The authors called the effect "puzzling", admitting they had expected formation of a volatile fluoride. [29] Ten years later, the compound was predicted to be non-volatile, out of line with the other halogens but similar to radon fluoride; [30] by this time, the latter had been shown to be ionic. [31]

Related Research Articles

Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours. A sample of the pure element has never been assembled, because any macroscopic specimen would be immediately vaporized by the heat of its own radioactivity.

<span class="mw-page-title-main">Bromine</span> Chemical element, symbol Br and atomic number 35

Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between those of chlorine and iodine. Isolated independently by two chemists, Carl Jacob Löwig and Antoine Jérôme Balard, its name was derived from the Ancient Greek βρῶμος (bromos) meaning "stench", referring to its sharp and pungent smell.

<span class="mw-page-title-main">Chlorine</span> Chemical element, symbol Cl and atomic number 17

Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine. On several scales other than the revised Pauling scale, nitrogen's electronegativity is also listed as greater than chlorine's, such as on the Allen, Allred-Rochow, Martynov-Batsanov, Mulliken-Jaffe, Nagle, and Noorizadeh-Shakerzadeh electronegativity scales.

<span class="mw-page-title-main">Halogen</span> Group of chemical elements

The halogens are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is known as group 17.

<span class="mw-page-title-main">Iodine</span> Chemical element, symbol I and atomic number 53

Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at 114 °C (237 °F), and boils to a violet gas at 184 °C (363 °F). The element was discovered by the French chemist Bernard Courtois in 1811 and was named two years later by Joseph Louis Gay-Lussac, after the Ancient Greek Ιώδης 'violet-coloured'.

In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (F2, Cl2, Br2, I2). Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride.

In chemistry, an interhalogen compound is a molecule which contains two or more different halogen atoms and no atoms of elements from any other group.

<span class="mw-page-title-main">Hydrogen halide</span> Chemical compound consisting of hydrogen bonded to a halogen element

In chemistry, hydrogen halides are diatomic, inorganic compounds that function as Arrhenius acids. The formula is HX where X is one of the halogens: fluorine, chlorine, bromine, iodine, or astatine. All known hydrogen halides are gases at Standard Temperature and Pressure.

<span class="mw-page-title-main">Zinc iodide</span> Chemical compound

Zinc iodide is the inorganic compound with the formula ZnI2. It exists both in anhydrous form and as a dihydrate. Both are white and readily absorb water from the atmosphere. It has no major application.

Bromine compounds are compounds containing the element bromine (Br). These compounds usually form the -1, +1, +3 and +5 oxidation states. Bromine is intermediate in reactivity between chlorine and iodine, and is one of the most reactive elements. Bond energies to bromine tend to be lower than those to chlorine but higher than those to iodine, and bromine is a weaker oxidising agent than chlorine but a stronger one than iodine. This can be seen from the standard electrode potentials of the X2/X− couples (F, +2.866 V; Cl, +1.395 V; Br, +1.087 V; I, +0.615 V; At, approximately +0.3 V). Bromination often leads to higher oxidation states than iodination but lower or equal oxidation states to chlorination. Bromine tends to react with compounds including M–M, M–H, or M–C bonds to form M–Br bonds.

<span class="mw-page-title-main">Hydrogen astatide</span> Chemical compound

Hydrogen astatide, also known as astatine hydride, astatane, astidohydrogen or hydroastatic acid, is a chemical compound with the chemical formula HAt, consisting of an astatine atom covalently bonded to a hydrogen atom. It thus is a hydrogen halide.

In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula AOmXn, where X = fluorine (F), chlorine (Cl), bromine (Br), and/or iodine (I). The element A may be a main group element, a transition element or an actinide. The term oxohalide, or oxyhalide, may also refer to minerals and other crystalline substances with the same overall chemical formula, but having an ionic structure.

<span class="mw-page-title-main">Astatine iodide</span> Chemical compound

Astatine iodide is an interhalogen compound with the chemical formula AtI. It is the second heaviest known interhalogen compound, after iodine tribromide.

<span class="mw-page-title-main">Lead compounds</span> Type of compound

Compounds of lead exist with lead in two main oxidation states: +2 and +4. The former is more common. Inorganic lead(IV) compounds are typically strong oxidants or exist only in highly acidic solutions.

<span class="mw-page-title-main">Astatine bromide</span> Chemical compound

Astatine bromide is an interhalogen compound with the chemical formula AtBr.

Polyhalogen ions are a group of polyatomic cations and anions containing halogens only. The ions can be classified into two classes, isopolyhalogen ions which contain one type of halogen only, and heteropolyhalogen ions with more than one type of halogen.

Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.

<span class="mw-page-title-main">Metals close to the border between metals and nonmetals</span> Category of metallic elements

The metallic elements in the periodic table located between the transition metals and the chemically weak nonmetallic metalloids have received many names in the literature, such as post-transition metals, poor metals, other metals, p-block metals and chemically weak metals; none have been recommended by IUPAC. The most common name, post-transition metals, is generally used in this article. Depending on where the adjacent sets of transition metals and metalloids are judged to begin and end, there are at least five competing proposals for which elements to count as post-transition metals: the three most common contain six, ten and thirteen elements, respectively. All proposals include gallium, indium, tin, thallium, lead, and bismuth.

Gallium compounds compounds containing the element gallium. These compounds are found primarily in the +3 oxidation state. The +1 oxidation state is also found in some compounds, although it is less common than it is for gallium's heavier congeners indium and thallium. For example, the very stable GaCl2 contains both gallium(I) and gallium(III) and can be formulated as GaIGaIIICl4; in contrast, the monochloride is unstable above 0 °C, disproportionating into elemental gallium and gallium(III) chloride. Compounds containing Ga–Ga bonds are true gallium(II) compounds, such as GaS (which can be formulated as Ga24+(S2−)2) and the dioxan complex Ga2Cl4(C4H8O2)2.

References

  1. ↑ Anders, E. (1959). "Technetium and astatine chemistry". Annual Review of Nuclear Science . 9: 203–220. Bibcode:1959ARNPS...9..203A. doi: 10.1146/annurev.ns.09.120159.001223 .(subscription required)
  2. ↑ Nefedov, V. D.; Norseev, Yu. V.; Toropova, M. A.; Khalkin, Vladimir A. (1968). "Astatine". Russian Chemical Reviews. 37 (2): 87–98. Bibcode:1968RuCRv..37...87N. doi:10.1070/RC1968v037n02ABEH001603. S2CID   250775410.(subscription required)
  3. ↑ Aten, A. H. W. Jr.; Doorgeest, T.; Hollstein, U.; Moeken, H. P. (1952). "Section 5: Radiochemical Methods. Analytical Chemistry of Astatine". Analyst. 77 (920): 774–777. Bibcode:1952Ana....77..774A. doi:10.1039/AN9527700774.(subscription required)
  4. 1 2 3 4 5 6 Zuckerman & Hagen 1989, p. 31.
  5. 1 2 Zuckerman & Hagen 1989, p. 38.
  6. ↑ Emsley, J. (2011). Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). Oxford University Press. pp. 57–58. ISBN   978-0-19-960563-7.
  7. ↑ Kugler & Keller 1985, pp. 213–214.
  8. ↑ Kugler & Keller 1985, pp. 214–218.
  9. ↑ Kugler & Keller 1985, p. 211.
  10. 1 2 Wiberg, N., ed. (2001). Holleman-Wiberg: Inorganic Chemistry. Translation of 101st German edition by M. Eagleson and W. D. Brewer, English language editor B. J. Aylett. Academic Press. p. 423. ISBN   978-0-12-352651-9.
  11. ↑ Kugler & Keller 1985, pp. 109–110, 129, 213.
  12. ↑ Davidson, M. (2000). Contemporary boron chemistry. Royal Society of Chemistry. p. 146. ISBN   978-0-85404-835-9.
  13. 1 2 3 4 Zuckerman & Hagen 1989, p. 276.
  14. ↑ Elgqvist, J.; Hultborn, R.; Lindegren, S.; Palm, S. (2011). "Ovarian cancer: background and clinical perspectives". In Speer, S. (ed.). Targeted Radionuclide Therapy. Lippincott Williams & Wilkins. pp. 380–396 (383). ISBN   978-0-7817-9693-4.
  15. 1 2 3 Zuckerman & Hagen 1989, pp. 190–191.
  16. ↑ Brookhart, M.; Grant, B.; Volpe, A. F. (1992). "[(3,5-(CF3)2C6H3)4B]-[H(OEt2)2]+: a convenient reagent for generation and stabilization of cationic, highly electrophilic organometallic complexes". Organometallics . 11 (11): 3920–3922. doi:10.1021/om00059a071.
  17. ↑ Kugler & Keller 1985, p. 111.
  18. ↑ Kugler & Keller 1985, p. 221.
  19. ↑ Sergentu, Dumitru-Claudiu; Teze, David; Sabatié-Gogova, Andréa; Alliot, Cyrille; Guo, Ning; Bassel, Fadel; Da Silva, Isidro; Deniaud, David; Maurice, Rémi; Champion, Julie; Galland, Nicolas; Montavon, Gilles (2016). "Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH)2− over At− in Basic Conditions". Chem. Eur. J. 22 (9): 2964–71. doi:10.1002/chem.201504403. PMID   26773333.
  20. ↑ Kugler & Keller 1985, p. 222.
  21. ↑ Lavrukhina & Pozdnyakov 1970, p. 238.
  22. 1 2 Kugler & Keller 1985, pp. 112, 192–193.
  23. ↑ Kugler & Keller 1985, p. 219.
  24. ↑ Zuckerman & Hagen 1989, pp. 192–193.
  25. ↑ Zuckerman & Hagen 1990, p. 212.
  26. ↑ Brinkman, G. A.; Aten, H. W. (1963). "Decomposition of Caesium Diiodo Astatate (I), (CsAtI2)". Radiochimica Acta. 2 (1): 48. doi:10.1524/ract.1963.2.1.48. S2CID   99398848.
  27. ↑ Zuckerman & Hagen 1990, p. 60.
  28. ↑ Zuckerman & Hagen 1989, p. 426.
  29. ↑ Appelman, E. H.; Sloth, E. N.; Studier, M. H. (1966). "Observation of Astatine Compounds by Time-of-Flight Mass Spectrometry". Inorganic Chemistry. 5 (5): 766–769. doi:10.1021/ic50039a016.
  30. ↑ Pitzer, K. S. (1975). "Fluorides of Radon and Element 118". Journal of the Chemical Society, Chemical Communications. 5 (18): 760b–761. doi:10.1039/C3975000760B.
  31. ↑ Bartlett, N.; Sladky, F. O. (1973). "The Chemistry of Krypton, Xenon and Radon". In Bailar, J. C.; Emeléus, H. J.; Nyholm, R.; et al. (eds.). Comprehensive Inorganic Chemistry. Vol. 1. Pergamon. pp. 213–330. ISBN   978-0-08-017275-0.

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