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'''Astatine compounds''' are compounds that contain the element [[astatine]] (At). Less reactive than iodine, astatine is the least reactive of the halogens.<ref name="Anders">{{cite journal | journal = [[Annual Review of Nuclear Science]] | volume = 9 | pages = 203–220 | year = 1959 | doi = 10.1146/annurev.ns.09.120159.001223|doi-access=free | title = Technetium and astatine chemistry | first = E. | last = Anders| bibcode = 1959ARNPS...9..203A }} {{subscription required}}</ref> Its [[chemical compound|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 (chemistry)|precipitation]]) to work.<ref name="Ru1968" /><ref>{{cite journal | journal =Analyst| year = 1952| volume = 77 | pages = 774–777| doi = 10.1039/AN9527700774 | title = Section 5: Radiochemical Methods. Analytical Chemistry of Astatine | first1 = A. H. W. Jr. | last1 = Aten| last2 =Doorgeest | first2 =T. | last3 =Hollstein | first3 =U.| last4 =Moeken | first4 =H. P. | issue =920| bibcode = 1952Ana....77..774A}} {{subscription required}}</ref>{{efn|Iodine can act as a carrier despite it reacting with astatine in water because these reactions require iodide (I<sup>−</sup>), not (only) I<sub>2</sub>.{{sfn|Zuckerman|Hagen|1989|p=31}}{{sfn|Zuckerman|Hagen|1989|p=38}}}} Like iodine, astatine has been shown to adopt odd-numbered oxidation states ranging from −1 to +7.

Only a few compounds with metals have been reported, in the form of astatides of sodium,<ref name="Emsley" /> [[palladium]], silver, [[thallium]], and lead.{{sfn|Kugler|Keller|1985|pp=213–214}} 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.{{sfn|Kugler|Keller|1985|pp=214–218}}

[[File:Hydrogen-astatide-calculated-3D-sf.svg|thumb|right|upright=0.6|[[Hydrogen astatide]]<!--Image captions don't count for overlinking&nbsp;– see [[WP:OVERLINK]] --> [[space-filling model]]]]

The formation of an astatine compound with hydrogen&nbsp;– usually referred to as hydrogen astatide&nbsp;– was noted by the pioneers of astatine chemistry.{{sfn|Kugler|Keller|1985|p=211}} As mentioned, there are grounds for instead referring to this compound as astatine hydride. It is easily [[oxidation (chemistry)|oxidized]]; acidification by dilute [[nitric acid]] gives the At<sup>0</sup> or At<sup>+</sup> 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 iodide|silver(I) iodide]].<ref name="MoreAtIC" />{{sfn|Kugler|Keller|1985|pp=109–110, 129, 213}}

Astatine is known to bind to [[boron]],<ref>{{cite book|title=Contemporary boron chemistry|first=M.|last=Davidson|page=146|year=2000 | publisher = Royal Society of Chemistry| isbn = 978-0-85404-835-9 |url = https://books.google.com/books?id=XWgD4uO1VCMC}}</ref> carbon, and [[nitrogen]].{{sfn|Zuckerman|Hagen|1989|p=276}} Various boron cage compounds have been prepared with At–B bonds, these being more stable than At–C bonds.<ref>{{cite book |last1=Elgqvist|first1=J. |last2=Hultborn|first2=R.|last3=Lindegren|first3=S.|last4=Palm|first4=S.|editor-last=Speer |editor-first=S. |title=Targeted Radionuclide Therapy|publisher=Lippincott Williams & Wilkins|date=2011 |pages=380–396 (383)|chapter=Ovarian cancer: background and clinical perspectives
|isbn=978-0-7817-9693-4}}</ref> Astatine can replace a hydrogen atom in [[benzene]] to form astatobenzene C<sub>6</sub>H<sub>5</sub>At; this may be oxidized to C<sub>6</sub>H<sub>5</sub>AtCl<sub>2</sub> by chlorine. By treating this compound with an [[base (chemistry)|alkaline]] solution of hypochlorite, C<sub>6</sub>H<sub>5</sub>AtO<sub>2</sub> can be produced.{{sfn|Zuckerman|Hagen|1989|pp=190–191}} The dipyridine-astatine(I) cation, [At(C<sub>5</sub>H<sub>5</sub>N)<sub>2</sub>]<sup>+</sup>, forms [[ionic compound]]s with [[perchlorate]]{{sfn|Zuckerman|Hagen|1989|p=276}} (a [[non-coordinating anion]]<ref>{{Cite journal|first1 = M.|last1 = Brookhart|author-link1 = Maurice Brookhart|first2 = B.|last2 = Grant|first3 = A. F.|last3 = Volpe|title = [(3,5-(CF<sub>3</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)<sub>4</sub>B]-[H(OEt<sub>2</sub>)<sub>2</sub>]<sup>+</sup>: a convenient reagent for generation and stabilization of cationic, highly electrophilic organometallic complexes|journal = [[Organometallics]]|year = 1992|volume = 11|issue = 11|pages = 3920–3922|doi = 10.1021/om00059a071}}</ref>) and with [[nitrate]], [At(C<sub>5</sub>H<sub>5</sub>N)<sub>2</sub>]NO<sub>3</sub>.{{sfn|Zuckerman|Hagen|1989|p=276}} This cation exists as a [[coordination complex]] in which two [[dative covalent bond]]s separately link the astatine(I) centre with each of the [[pyridine]] rings via their nitrogen atoms.{{sfn|Zuckerman|Hagen|1989|p=276}}

With oxygen, there is evidence of the species AtO<sup>−</sup> and AtO<sup>+</sup> 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]]:<ref name="MoreAtIC" />{{sfn|Kugler|Keller|1985|p=111}} the latter species might also be protonated astatous acid, {{chem|H|2|AtO|2|+}}.{{sfn|Kugler|Keller|1985|p=221}} The species previously thought to be {{chem|AtO|2|-}} has since been determined to be {{chem|AtO(OH)|2|-}}, a hydrolysis product of AtO<sup>+</sup> (another such hydrolysis product being AtOOH).<ref>{{cite journal |last1=Sergentu |first1=Dumitru-Claudiu |last2=Teze |first2=David |first3=Andréa |last3=Sabatié-Gogova |first4=Cyrille |last4=Alliot |first5=Ning |last5=Guo |first6=Fadel |last6=Bassel |first7=Isidro |last7=Da Silva |first8=David |last8=Deniaud |first9=Rémi |last9=Maurice |first10=Julie |last10=Champion |first11=Nicolas |last11=Galland |first12=Gilles |last12=Montavon |title=Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH)<sub>2</sub><sup>−</sup> over At<sup>−</sup> in Basic Conditions |journal=Chem. Eur. J. |year=2016 |volume=22 |issue=9 |pages=2964–71 |doi=10.1002/chem.201504403|pmid=26773333 }}</ref> The well characterized {{chem|AtO|3|-}} anion can be obtained by, for example, the oxidation of astatine with potassium hypochlorite in a solution of [[potassium hydroxide]].{{sfn|Zuckerman|Hagen|1989|pp = 190–191}}{{sfn|Kugler|Keller|1985|p=222}} Preparation of [[lanthanum]] triastatate La(AtO<sub>3</sub>)<sub>3</sub>, following the oxidation of astatine by a hot Na<sub>2</sub>S<sub>2</sub>O<sub>8</sub> solution, has been reported.{{sfn|Lavrukhina|Pozdnyakov|1970|p=238}} Further oxidation of {{chem|AtO|3|-}}, such as by [[xenon difluoride]] (in a hot alkaline solution) or [[periodate]] (in a [[neutral solution|neutral]] or alkaline solution), yields the perastatate ion {{chem|AtO|4|-}}; this is only stable in neutral or alkaline solutions.{{sfn|Kugler|Keller|1985|pp=112, 192–193}} 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.{{sfn|Zuckerman|Hagen|1989|pp=190–191}}{{sfn|Kugler|Keller|1985|p=219}}

Astatine may form bonds to the other [[chalcogen]]s; these include S<sub>7</sub>At<sup>+</sup> and {{chem|At(CSN)|2|-}} with [[sulfur]], a coordination [[selenourea]] compound with [[selenium]], and an astatine–[[tellurium]] [[colloid]] with tellurium.{{sfn|Zuckerman|Hagen|1989|pp=192–193}}

[[File:Astatine-iodide-3D-vdW.svg|thumb|right|upright=0.9|Structure of astatine monoiodide, one of the astatine [[interhalogen]]s 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 compound]]s with formulas AtI, AtBr, and AtCl.{{sfn|Zuckerman|Hagen|1989|p=31}} The first two compounds may also be produced in water&nbsp;– 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 {{chem|AtBr|2|-}} and {{chem|AtI|2|-}} ions,{{sfn|Zuckerman|Hagen|1989|p=31}} or in a chloride solution, they may produce species like {{chem|AtCl|2|-}} or {{chem|AtBrCl|-}} via equilibrium reactions with the chlorides.{{sfn|Zuckerman|Hagen|1989|p=38}} 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, {{chem|AtOCl|2|-}} or {{chem|AtCl|2|-}} may be produced.{{sfn|Zuckerman|Hagen|1989|p=31}} The polyhalides PdAtI<sub>2</sub>, CsAtI<sub>2</sub>, TlAtI<sub>2</sub>,{{sfn|Zuckerman|Hagen|1990|p=212}}<ref>{{cite journal |first1=G. A.|last1=Brinkman |first2=H. W.|last2=Aten|year=1963 |title=Decomposition of Caesium Diiodo Astatate (I), (CsAtI<sub>2</sub>) |journal=Radiochimica Acta |volume=2 |issue=1|page=48 |doi=10.1524/ract.1963.2.1.48|s2cid=99398848 }}</ref>{{sfn|Zuckerman|Hagen|1990|p=60}} and PbAtI{{sfn|Zuckerman|Hagen|1989|p=426}} are known or presumed to have been precipitated. In a plasma ion source [[mass spectrometry|mass spectrometer]], the ions [AtI]<sup>+</sup>, [AtBr]<sup>+</sup>, and [AtCl]<sup>+</sup> 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.{{sfn|Zuckerman|Hagen|1989|p=31}} No astatine fluorides<!--AtF, AtF5, or whatever else, "no" means "no" (not AtF, not AtF5, not At45F387, or whatever)--> 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.{{efn|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.<ref>{{cite journal |first1=E. H.|last1=Appelman|first2=E. N.|last2=Sloth|first3=M. H. |last3=Studier |year=1966 |title=Observation of Astatine Compounds by Time-of-Flight Mass Spectrometry |journal=Inorganic Chemistry |volume=5 |issue = 5|pages=766–769 |doi=10.1021/ic50039a016}}</ref> Ten years later, the compound was predicted to be non-volatile, out of line with the other halogens but similar to [[radon difluoride|radon fluoride]];<ref>{{cite journal |first1=K. S.|last1=Pitzer|year=1975 |title=Fluorides of Radon and Element 118 |journal=Journal of the Chemical Society, Chemical Communications |volume=5 |issue = 18|pages=760b–761 |doi=10.1039/C3975000760B|url=https://escholarship.org/uc/item/8xz4g1ff}}</ref> by this time, the latter had been shown to be ionic.<ref>{{cite encyclopedia | last1 = Bartlett | first1 = N. | last2 = Sladky | first2 = F. O. | editor1-first = J. C. | editor1-last = Bailar | editor2-first= H. J. | editor2-last = Emeléus | editor3-first = R. | editor3-last = Nyholm | editor4-first = A. F. | editor4-last = Trotman-Dickenson | display-editors=3| encyclopedia =Comprehensive Inorganic Chemistry | title = The Chemistry of Krypton, Xenon and Radon | year = 1973 | publisher = Pergamon | volume = 1 | isbn = 978-0-08-017275-0 | pages =213–330}}</ref>}} 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.{{sfn|Zuckerman|Hagen|1989|p=31}}{{sfn|Kugler|Keller|1985|pp=112, 192–193}}

== Notes ==

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== References ==

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[[:Category:Astatine compounds]]
[[:Category:Astatine]]
[[:Category:Chemical compounds by element]]