Editing Group 7 element (section)

=== Halides ===

==== Manganese ====

Manganese can form compounds in the +2, +3 and +4 oxidation states. The manganese(II) compounds are often light pink solids. Like some other metal difluorides, MnF<sub>2</sub> crystallizes in the [[rutile]] structure, which features octahedral Mn centers.<ref>{{cite journal |doi=10.1021/ja01650a005|title=The Crystal Structure of MnF<sub>2</sub>, FeF<sub>2</sub>, CoF<sub>2</sub>, NiF<sub>2</sub> and ZnF<sub>2</sub>|first1=J. W.|last1=Stout|first2=Stanley A.|last2=Reed|journal= J. Am. Chem. Soc.|year=1954|volume=76|issue=21|pages=5279–5281}}</ref> and it  is used in the manufacture of special kinds of [[glass]] and [[laser]]s.<ref>
{{Cite book | last1 = Ayres | first1 = D. C. | last2 = Hellier | first2 = Desmond | year = 1997 | title = Dictionary of Environmentally Important Chemicals | publisher = CRC Press | isbn = 0-7514-0256-7 | pages = 195 | url = https://books.google.com/books?id=UTKWehimCkEC&q=%22Manganese(II)+fluoride+%22&pg=PA195 | access-date = 2008-06-18 }}</ref> Scacchite is the natural, anhydrous form of manganese(II) chloride.<ref>{{Cite web|url=https://www.mindat.org/min-3549.html|title=Scacchite}}</ref> The only other currently known mineral systematized as manganese chloride is kempite - a representative of the atacamite group, a group of hydroxide-chlorides.<ref>{{Cite web|url=https://www.mindat.org/min-2183.html|title=Kempite}}</ref> It can be used in place of [[palladium]] in the [[Stille reaction]], which couples two carbon atoms using an [[organotin compound]].<ref name="Mn(II) halide" /> It can be used as a pink pigment or as a source of the manganese ion or iodide ion. It is often used in the lighting industry.<ref name="Mn(II) halide">{{Cite book | last = Cepanec | first = Ivica  | author-link =  | year = 2004 | title = Synthesis of Biaryls | edition = | volume = | series = | publication-place =  | place =  | publisher = Elsevier | id = | isbn = 0-08-044412-1 | doi = | oclc = | pages = 104 | url = https://books.google.com/books?id=UMLOo1wXWdwC&dq=%22Manganese(II)+bromide+%22&pg=PA104 | accessdate = 2008-06-18 }}</ref>

==== Technetium ====

The following binary (containing only two elements) technetium halides are known: [[TcF6|TcF<sub>6</sub>]], TcF<sub>5</sub>, [[TcCl4|TcCl<sub>4</sub>]], TcBr<sub>4</sub>, TcBr<sub>3</sub>, α-TcCl<sub>3</sub>, β-TcCl<sub>3</sub>, TcI<sub>3</sub>, α-TcCl<sub>2</sub>, and β-TcCl<sub>2</sub>. The [[oxidation state]]s range from Tc(VI) to Tc(II). Technetium halides exhibit different structure types, such as molecular octahedral complexes, extended chains, layered sheets, and metal clusters arranged in a three-dimensional network.<ref>{{Cite thesis|title=Binary Technetium Halides |last=Johnstone|first=E. V. |date=May 2014 |publisher=University of Nevada, Las Vegas |url=http://digitalscholarship.unlv.edu/cgi/viewcontent.cgi?article=3100&context=thesesdissertations |doi=10.34917/5836118 |via=UNLV Theses, Dissertations, Professional Papers, and Capstones}}</ref><ref name="AS">{{cite journal|doi=10.1021/ar400225b |pmid=24393028|title=Recent Advances in Technetium Halide Chemistry|journal=Accounts of Chemical Research|volume=47|issue=2|pages=624–632 |year=2014|last1=Poineau |first1=Frederic|last2=Johnstone|first2=Erik V.|last3=Czerwinski|first3=Kenneth R.|last4=Sattelberger |first4=Alfred P.}}</ref> These compounds are produced by combining the metal and halogen or by less direct reactions.

TcCl<sub>4</sub> is obtained by chlorination of Tc metal or Tc<sub>2</sub>O<sub>7</sub> Upon heating, TcCl<sub>4</sub> gives the corresponding Tc(III) and Tc(II) chlorides.<ref name="AS" />
:TcCl<sub>4</sub> → α-TcCl<sub>3</sub> + 1/2 Cl<sub>2</sub>
:TcCl<sub>3</sub> → β-TcCl<sub>2</sub> + 1/2 Cl<sub>2</sub>
The structure of TcCl<sub>4</sub> is composed of infinite zigzag chains of edge-sharing TcCl<sub>6</sub> octahedra. It is isomorphous to transition metal tetrachlorides of [[zirconium]], [[hafnium]], and [[platinum]].<ref name="AS"/>
[[File:Chloro-containing coordination complexes of technetium (Tc-99).jpg|thumb|Chloro-containing coordination complexes of technetium (Tc-99) in various oxidation states: Tc(III), Tc(IV), Tc(V), and Tc(VI) represented.]]

Two polymorphs of [[technetium trichloride]] exist, α- and β-TcCl<sub>3</sub>. The α polymorph is also denoted as Tc<sub>3</sub>Cl<sub>9</sub>. It adopts a confacial [[Octahedral molecular geometry#Bioctahedral molecular geometry|bioctahedral structure]].<ref>{{cite journal|doi=10.1021/ja105730e|pmid=20977207|title=Synthesis and Structure of Technetium Trichloride|journal=Journal of the American Chemical Society|volume=132|issue=45|pages=15864–5|year=2010|last1=Poineau|first1=Frederic|last2=Johnstone|first2=Erik V.|last3=Weck|first3=Philippe F.|last4=Kim|first4=Eunja|last5=Forster|first5=Paul M.|last6=Scott|first6=Brian L.|last7=Sattelberger|first7=Alfred P.|last8=Czerwinski|first8=Kenneth R.}}</ref> It is prepared by treating the chloro-acetate Tc<sub>2</sub>(O<sub>2</sub>CCH<sub>3</sub>)<sub>4</sub>Cl<sub>2</sub> with HCl. Like [[Trirhenium nonachloride|Re<sub>3</sub>Cl<sub>9</sub>]], the structure of the α-polymorph consists of triangles with short M-M distances. β-TcCl<sub>3</sub> features octahedral Tc centers, which are organized in pairs, as seen also for [[molybdenum trichloride]]. TcBr<sub>3</sub> does not adopt the structure of either trichloride phase. Instead it has the structure of [[molybdenum tribromide]], consisting of chains of confacial octahedra with alternating short and long Tc—Tc contacts. TcI<sub>3</sub> has the same structure as the high temperature phase of [[titanium(III) iodide|TiI<sub>3</sub>]], featuring chains of confacial octahedra with equal Tc—Tc contacts.<ref name="AS" />

Several anionic technetium halides are known. The binary tetrahalides can be converted to the hexahalides [TcX<sub>6</sub>]<sup>2−</sup> (X = F, Cl, Br, I), which adopt [[octahedral molecular geometry]].<ref name="s8">{{harvnb|Schwochau|2000|pp=7–9}}</ref> More reduced halides form anionic clusters with Tc–Tc bonds. The situation is similar for the related elements of Mo, W, Re. These clusters have the nuclearity Tc<sub>4</sub>, Tc<sub>6</sub>, Tc<sub>8</sub>, and Tc<sub>13</sub>. The more stable Tc<sub>6</sub> and Tc<sub>8</sub> clusters have prism shapes where vertical pairs of Tc atoms are connected by triple bonds and the planar atoms by single bonds. Every technetium atom makes six bonds, and the remaining valence electrons can be saturated by one axial and two [[bridging ligand]] halogen atoms such as [[chlorine]] or [[bromine]].<ref>{{cite journal|first1 = K. E.|last1 = German|last2 = Kryutchkov|first2 = S. V.|title = Polynuclear Technetium Halide Clusters|journal = Russian Journal of Inorganic Chemistry|volume = 47|issue = 4|date = 2002|pages = 578–583|url = http://www.maik.rssi.ru/cgi-perl/search.pl?type=abstract&name=inrgchem&number=4&year=2&page=578|archive-url = https://web.archive.org/web/20151222111809/http://www.maik.rssi.ru/cgi-perl/search.pl?type=abstract&name=inrgchem&number=4&year=2&page=578|url-status = dead|archive-date = 2015-12-22}}</ref>

==== Rhenium ====

The most common rhenium chlorides are [[Rhenium hexachloride|ReCl<sub>6</sub>]], [[Rhenium pentachloride|ReCl<sub>5</sub>]], [[Rhenium tetrachloride|ReCl<sub>4</sub>]], and [[Rhenium trichloride|ReCl<sub>3</sub>]].<ref name="G&W">{{Greenwood&Earnshaw2nd}}</ref> The structures of these compounds often feature extensive Re-Re bonding, which is characteristic of this metal in oxidation states lower than VII. Salts of [Re<sub>2</sub>Cl<sub>8</sub>]<sup>2−</sup> feature a [[quadruple bond|quadruple]] metal-metal bond. Although the highest rhenium chloride features Re(VI), fluorine gives the d<sup>0</sup> Re(VII) derivative [[rhenium heptafluoride]]. Bromides and iodides of rhenium are also well known.

Like tungsten and molybdenum, with which it shares chemical similarities, rhenium forms a variety of [[Oxohalide|oxyhalides]]. The oxychlorides are most common, and include ReOCl<sub>4</sub>, ReOCl<sub>3</sub>.