Mercury polycations

From Wikipedia, the free encyclopedia

Mercury polycations are polyatomic cations that contain only mercury atoms. The best known example is the Hg2+
2
ion, found in mercury(I) (mercurous) compounds. The existence of the metal–metal bond in Hg(I) compounds was established using X-ray studies in 1927[1][page needed] and Raman spectroscopy in 1934[2] making it one of the earliest, if not the first, metal–metal covalent bonds to be characterised.

Other mercury polycations are the linear Hg2+
3
and Hg2+
4
ions,[2] and the triangular Hg4+
3
ion [3] and a number of chain[4] and layer polycations.[5]

Mercury(I)[]

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.[6] In 1900, Baker showed the presence of HgCl dimers in the vapour phase.[7] The presence of Hg2+
2
units in the solid state was first determined in 1926 using X-ray diffraction.[1] The presence of the metal-metal bond in solution was confirmed using Raman spectroscopy in 1934.[2]

Hg2+
2
is stable in aqueous solution, where it is in equilibrium with Hg2+
and elemental Hg, with Hg2+
present at around 0.6%.[2] This equilibrium is readily shifted by the addition of an anion which forms an insoluble Hg(II) salt, such as S2−
, which causes the Hg(I) salt to completely disproportionate, or by the addition of an anion which forms an insoluble Hg(I) salt, such as Cl
, which causes the elemental mercury and Hg2+ to completely recombine into the mercury(I) salt.[2]

Minerals that are known that contain the Hg2+
2
cation include .[8]

Linear trimercury and tetramercury cations[]

Compounds containing the linear Hg2+
3
(mercury(23)) and Hg2+
4
(mercury(12)) cations have been synthesised. These ions are only known in the solid state in compounds such as Hg
3
(AlCl
4
)
2
and Hg
4
(AsF
6
)
2
.[2] The Hg–Hg bond length is 255 pm in Hg2+
3
, and 255–262 pm in Hg2+
4
.[2] The bonding involves 2-centre-2-electron bonds formed by 6s orbitals.[2]

Cyclic mercury cations[]

The triangular Hg4+
3
cation was confirmed in a reinvestigation of the mineral terlinguaite in 1989[3] and subsequently synthesised in a number of compounds.[9] The bonding has been described in terms of a three-center two-electron bond where overlap of the 6s orbitals on the mercury atoms gives (in D3h symmetry) a bonding "a1" orbital.[10]

Chain and layer polycations[]

The golden yellow compound Hg
2.86
(AsF
6
), named "alchemists' gold" by its discoverers,[4] contains perpendicular chains of Hg atoms.

The "metallic" compounds Hg
3
NbF
6
and Hg
3
TaF
6
contain hexagonal layers of mercury atoms separated by layers of MF
6
anions.[5] They are both superconductors below 7 K.[11]

References[]

  1. ^ a b Wells, A. F. (1962). Structural Inorganic Chemistry (3rd ed.). Oxford Science Publications.
  2. ^ a b c d e f g h Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  3. ^ a b Brodersen, K.; Göbel, G.; Liehr, G. (1989). "Terlinguait Hg4O2Cl2 - ein Mineral mit ungewöhnlichen Hg3-Baueinheiten". Zeitschrift für anorganische und allgemeine Chemie (in German). Wiley. 575 (1): 145–153. doi:10.1002/zaac.19895750118. ISSN 0044-2313.
  4. ^ a b 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)
  5. ^ a b Brown, I. D.; Gillespie, R. J.; Morgan, K. R.; Tun, Z.; Ummat, P. K. (1984). "Preparation and crystal structure of mercury hexafluoroniobate (Hg
    3
    NbF
    6
    ) and mercury hexafluorotantalate (Hg
    3
    TaF
    6
    ): mercury layer compounds". Inorganic Chemistry. 23 (26): 4506–4508. doi:10.1021/ic00194a020.
  6. ^ A. Ogg; Zeitschrift Physische Chemie 27, 285 (1898)
  7. ^ Baker, H. Brereton (1900). "LII.—Vapour density of dried mercurous chloride". J. Chem. Soc., Trans. Royal Society of Chemistry (RSC). 77: 646–648. doi:10.1039/ct9007700646. ISSN 0368-1645.
  8. ^ 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
  9. ^ Borisov, S. V.; Magarill, S. A.; Pervukhina, N. V. (2003). "[Hg3]4+Cation in Inorganic Crystal Structures". Journal of Structural Chemistry. Springer Science and Business Media LLC. 44 (3): 441–447. doi:10.1023/b:jory.0000009672.71752.68. ISSN 0022-4766. S2CID 95647246.
  10. ^ 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. Royal Society of Chemistry (RSC) (9): 1607–1610. doi:10.1039/a700483d. ISSN 0300-9246.
  11. ^ Datars, W. R.; Morgan, K. R.; Gillespie, R. J. (1983-11-01). "Superconductivity of Hg3NbF6 and Hg3TaF6". Physical Review B. American Physical Society (APS). 28 (9): 5049–5052. doi:10.1103/physrevb.28.5049. ISSN 0163-1829.
Retrieved from ""