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Mercury polycations
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<h2 id="mercuryi">Mercury(I)</h2> <p>The best known polycation of mercury is Hg2+2, in which mercury has a formal oxidation state of +1. The Hg2+2 ion was perhaps the first metal-metal bonded species confirmed. The presence of the Hg2+2 ion in solution was shown by Ogg in 1898.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> In 1900, Baker showed the presence of HgCl dimers in the vapour phase.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> The presence of Hg2+2 units in the solid state was first determined in 1926 using X-ray diffraction.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> The presence of the metal-metal bond in solution was confirmed using Raman spectroscopy in 1934.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p><p>Hg2+2 is stable in aqueous solution, where it is in equilibrium with Hg2+ and elemental Hg, with Hg2+ present at around 0.6%. Anions of insoluble salts readily shift the equilibrium: <a href="/facts/Sulfide/d8YMjLeu">S2−</a>, which forms an insoluble Hg(II) salt, induces complete disproportionation, whereas <a href="/facts/Chloride/m9NUaUDR">Cl−</a>, which forms an insoluble Hg(I) salt, induces the reverse.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> Most salts with <a href="/facts/Main_group_element/2AG3QxJl">main group elements</a> tend to contain only Hg(II) and metallic mercury, because the presence of strong <a href="/facts/Lewis_base/qlLqRvg2">Lewis bases</a> destabilizes the intermetallic bond. In appropriate solvents, however, Hg(I) salts with derivatives of <a href="/facts/Amide/C6kCzYEA">amides</a>, <a href="/facts/Pyridine/X817hCch">pyridines</a>, <a href="/facts/Phosphorus_trifluoride/feeXrTsB">phosphorus trifluoride</a>, <a href="/facts/Tin(II)/obW9mqc3">tin(II)</a>, and certain other main group elements are all known.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p><p>Minerals that are known that contain the Hg2+2 cation include eglestonite.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p> <h2 id="linear-trimercury-and-tetramercury-cations">Linear trimercury and tetramercury cations</h2> <p>Compounds containing the linear Hg2+3 (in which mercury has the formal oxidation state 2⁄3) and Hg2+4 (in which mercury has the formal oxidation state 1⁄2) cations have been synthesised. These ions are only known in the solid state in compounds such as Hg3(AlCl4)2 and Hg4(AsF6)2. The Hg–Hg bond length is 255 pm in Hg2+3, and 255–262 pm in Hg2+4. The bonding involves 2-centre-2-electron bonds formed by 6s orbitals.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h2 id="cyclic-mercury-cations">Cyclic mercury cations</h2> <p>The triangular Hg4+3 cation was confirmed in a reinvestigation of the mineral <a href="/facts/Terlinguaite/ycdAt8z0">terlinguaite</a> in 1989<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> and subsequently synthesised in a number of compounds.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> The bonding has been described in terms of a <a href="/facts/Three-center_two-electron_bond/1etgQjYh">three-center two-electron bond</a> where overlap of the 6s orbitals on the mercury atoms gives (in D3h symmetry) a bonding "a1" orbital.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> </p> <h2 id="chain-and-layer-polycations">Chain and layer polycations</h2> <p>The golden yellow compound Hg2.86(AsF6), named "alchemists' gold" by its discoverers,<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> contains perpendicular chains of Hg atoms. </p><p>The "metallic" compounds Hg3NbF6 and Hg3TaF6 contain hexagonal layers of mercury atoms separated by layers of MF−6 anions.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> They are both <a href="/facts/Superconductor/pqQAlSzJ">superconductors</a> below 7 <a href="/facts/Kelvin/E3trzC4C">K</a>.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Wells, A. F. (1962). Structural Inorganic Chemistry (3rd ed.). Oxford Science Publications. <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Brodersen, K.; Göbel, G.; Liehr, G. (1989). "Terlinguait Hg4O2Cl2 - ein Mineral mit ungewöhnlichen Hg3-Baueinheiten". Zeitschrift für anorganische und allgemeine Chemie (in German). 575 (1). Wiley: 145–153. doi:10.1002/zaac.19895750118. ISSN 0044-2313. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>I. David Brown, Brent D. Cutforth, Colin G. Davies, Ronald J. Gillespie, Peter R. Ireland, and John E. Vekris (1974). "Alchemists' Gold, Hg2.86 AsF6; An X-Ray Crystallographic Study of A Novel Disordered Mercury Compound Containing Metallically Bonded Infinite Cations". Can. J. Chem. 52 (5): 791–793. doi:10.1139/v74-124. S2CID 93164215.{{cite journal}}: CS1 maint: multiple names: authors list (link) <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Brown, I. D.; Gillespie, R. J.; Morgan, K. R.; Tun, Z.; Ummat, P. K. (1984). "Preparation and crystal structure of mercury hexafluoroniobate (Hg3NbF6) and mercury hexafluorotantalate (Hg3TaF6): mercury layer compounds". Inorganic Chemistry. 23 (26): 4506–4508. doi:10.1021/ic00194a020. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>A. Ogg; Zeitschrift Physische Chemie 27, 285 (1898) <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Baker, H. Brereton (1900). "LII.—Vapour density of dried mercurous chloride". J. Chem. Soc., Trans. 77. Royal Society of Chemistry (RSC): 646–648. doi:10.1039/ct9007700646. ISSN 0368-1645. <a href="https://zenodo.org/record/1573673" target="_blank">https://zenodo.org/record/1573673</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Wells, A. F. (1962). Structural Inorganic Chemistry (3rd ed.). Oxford Science Publications. <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Brodersen, Klaus (1981). "Dimercury(I)-Nitrogen Compounds and Other Addition Complexes of the +Hg-Hg+ Ion". Comments on Inorganic Chemistry. 1 (4). Gordon & Breach (published 19 Dec 2006): 207–225. doi:10.1080/02603598108078093. <a href="/wiki/Gordon_%26_Breach" target="_blank">/wiki/Gordon_%26_Breach</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Eglestonite, [Hg2]3Cl3O2H: Confirmation of the chemical formula by neutron powder diffraction, Mereiter K., Zemann J., Hewatt A.W. American Mineralogist, 77, (1992), 839-842 <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Brodersen, K.; Göbel, G.; Liehr, G. (1989). "Terlinguait Hg4O2Cl2 - ein Mineral mit ungewöhnlichen Hg3-Baueinheiten". Zeitschrift für anorganische und allgemeine Chemie (in German). 575 (1). Wiley: 145–153. doi:10.1002/zaac.19895750118. ISSN 0044-2313. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Borisov, S. V.; Magarill, S. A.; Pervukhina, N. V. (2003). "[Hg3]4+ Cation in Inorganic Crystal Structures". Journal of Structural Chemistry. 44 (3). Springer Science and Business Media LLC: 441–447. doi:10.1023/b:jory.0000009672.71752.68. ISSN 0022-4766. S2CID 95647246. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Mühlecker-Knoepfler, Anna; Ellmerer-Müller, Ernst; Konrat, Robert; Ongania, Karl-Hans; Wurst, Klaus; Peringer, Paul (1997). "Synthesis and crystal structure of the subvalent mercury cluster [triangulo-Hg3(μ-dmpm)4][O3SCF3]4 (dmpm = Me2PCH2PMe2)". Journal of the Chemical Society, Dalton Transactions (9). Royal Society of Chemistry (RSC): 1607–1610. doi:10.1039/a700483d. ISSN 0300-9246. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>I. David Brown, Brent D. Cutforth, Colin G. Davies, Ronald J. Gillespie, Peter R. Ireland, and John E. Vekris (1974). "Alchemists' Gold, Hg2.86 AsF6; An X-Ray Crystallographic Study of A Novel Disordered Mercury Compound Containing Metallically Bonded Infinite Cations". Can. J. Chem. 52 (5): 791–793. doi:10.1139/v74-124. S2CID 93164215.{{cite journal}}: CS1 maint: multiple names: authors list (link) <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Brown, I. D.; Gillespie, R. J.; Morgan, K. R.; Tun, Z.; Ummat, P. K. (1984). "Preparation and crystal structure of mercury hexafluoroniobate (Hg3NbF6) and mercury hexafluorotantalate (Hg3TaF6): mercury layer compounds". Inorganic Chemistry. 23 (26): 4506–4508. doi:10.1021/ic00194a020. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Datars, W. R.; Morgan, K. R.; Gillespie, R. J. (1983-11-01). "Superconductivity of Hg3NbF6 and Hg3TaF6". Physical Review B. 28 (9). American Physical Society (APS): 5049–5052. Bibcode:1983PhRvB..28.5049D. doi:10.1103/physrevb.28.5049. ISSN 0163-1829. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> </ol>