Potassium tetraiodomercurate(II)

{{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 439640770 | Name = | ImageFile = Nessler's-reagent-2D.png | ImageName = | ImageFile1 = Nessler's-reagent-3D-vdW.png | ImageSize1 = | IUPACName = potassium tetraiodidomercurate(II) | OtherNames = potassium mercuric iodide,
Nessler's reagent (principal component) | SystematicName = | Section1 = !Identifiers

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3D model (JSmol)

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| ChEBI

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| ChemSpider

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| ECHA InfoCard | 100.029.082 |- | EC Number

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  • 231-990-4

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| UNII

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|- | UN number | 3287 |-

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  • InChI=1S/Hg.4HI.2K/h;4*1H;;/q+2;;;;;2*+1/p-4 ☒N
    Key: OPCMAZHMYZRPID-UHFFFAOYSA-J ☒N

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  • [K+].[K+].I[Hg-2](I)(I)I

|- | Section2 = !Properties

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| K2[HgI4][1]

|- | Molar mass

| 786.406 g·mol−1

|- | Appearance | yellow crystals |- | Odor | odorless |- | Density | 4.29 g/cm3 |-



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| very soluble |-

| Solubility | soluble in alcohol, ether, acetone |- | Section3 = | Section4 = | Section5 = | Section6 = | Section7 = {{Chembox Hazards | ExternalSDS = External MSDS for Nessler's reagent | HPhrases = | PPhrases = | GHS_ref = | NFPA-H = | NFPA-F </ref>

Preparation and structure

Crystallizing from a concentrated aqueous solution of mercuric iodide with potassium iodide is the monohydrate K2[HgI4]·H2O, which is pale orange.[2] In aqueous solution this triiodido complex adds iodide to give the tetrahedral tetraiodo dianion.[3]

Solutions of K2[HgI4] react with Cu(I) salts to give Cu2[HgI4] (copper(I) tetraiodomercurate(II)).[4]

Nessler's reagent

Nessler's reagent, named after Julius Neßler (Nessler), is a 0.09 mol/L solution of potassium tetraiodomercurate(II) in 2.5 mol/L potassium hydroxide. This pale solution becomes deeper yellow in the presence of ammonia (NH3). At higher concentrations, a brown precipitate of iodide of Millon's base (HgO·Hg(NH2)I) may form. The sensitivity as a spot test is about 0.3 μg NH3 in 2 μL.[5]

NH+4 + 2 [HgI4]2− + 4 OH− → HgO·Hg(NH2)I↓ + 7 I− + 3 H2O

The formula for the brown precipitate, a derivative of Millon's base, is given as 3HgO·Hg(NH3)2I2 and as NH2·Hg2I3.[6]

References
  1. Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. p. 4-82. ISBN 978-1-4200-9084-0.
  2. Wagenknecht, F.; Juza, R. (1963). "Potassium Triiodomercurate(II)". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). Academic Press. p. 1100.
  3. Mok, K. F.; McKee, V. (1990). "Structure of a dipotassium tetraiodomercurate(II) salt with dibenzo-18-crown-6". Acta Crystallographica C. 46 (11): 2078–2081. doi:10.1107/S0108270190003742.
  4. Wagenknecht, F.; Juza, R. (1963). "Copper(I) Tetraiodomercurate(II)". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). Academic Press. p. 1100.
  5. Vogel, Arthur I. (1954), A Textbook of Macro and Semimicro Qualitative Inorganic Analysis (4th ed.), London: Longman, p. 319, ISBN 0-582-44367-9
  6. Vogel, Arthur I.; Svehla, G. (1979), Vogel's Textbook of Macro and Semimicro Qualitative Inorganic Analysis (5th ed.), London: Longman, pp. 293–294, ISBN 0-582-44367-9
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