Nickel(II) chromate

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Nickel chromate
Names
IUPAC name
Nickel(II) chromate
Other names
nickelous chromate
nickel chromate
nickel(II) chromium(VI) oxide
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.035.227 Edit this at Wikidata
EC Number
  • 238-766-5
  • InChI=1S/Cr.Ni.4O/q;+2;;;2*-1
    Key: QGAXAFUJMMYEPE-UHFFFAOYSA-N
SMILES
  • [O-][Cr](=O)(=O)[O-].[Ni+2]
Properties
NiCrO4
Molar mass 174.71 g/mol
Appearance dark maroon-colored powder
very slightly soluble in water[1]
Solubility soluble in hydrochloric acid
Hazards
Flash point Non-flammable
Related compounds
Other anions
nickel(II) tungstate
Other cations
 magnesium chromate
cadmium chromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Nickel(II) chromate (NiCrO4) is an acid-soluble compound, red-brown in color, with high tolerances for heat. It and the ions that compose it have been linked to tumor formation and gene mutation, particularly to wildlife.[2]

Synthesis

Nickel(II) chromate can be formed in the lab by heating a mixture of chromium(III) oxide and nickel oxide at between 700 °C and 800 °C under oxygen at 1000 atm pressure. It can be produced at 535 °C and 7.3 bar oxygen, but the reaction takes days to complete.[3] If the pressure is too low or temperature too high but above 660 °C, then the nickel chromium spinel NiCr2O4 forms instead.[3]

Karin Brandt also claimed to make nickel chromate using a hydrothermal technique.[4][5]

Precipitates of Ni2+ ions with chromate produce a brown substance that contains water.[6]

Properties

The structure of nickel chromate is the same as for chromium vanadate, CrVO4. Crystals have an orthorhombic structure with unit cell sizes a = 5.482 Å, b = 8.237 Å, c = 6.147 Å. The cell volume is 277.6 Å3 with four formula per unit cell.[5][7]

Nickel chromate is dark in colour, unlike most other chromates which are yellow.[3] The infrared spectrum of nickel chromate show two sets of absorption bands. The first includes lines at 925, 825, and 800 cm−1 due to Cr-O stretching, and the second has lines at 430, 395, 365 (very weak) due to Cr-O rock and bend and 310 cm−1 produced from Ni-O stretching.[8]

Reaction

When heated at lower oxygen pressure around 600 °C, nickel chromate decomposes to the nickel chromite spinel, nickel oxide and oxygen.[3]

4 NiCrO4 → 2 NiCr2O4 + 2 NiO + 3 O2 (gas)

Nickel chromates can also crystallize with ligands. For instance, with

1,10-phenanthroline it can form triclinic olive-colored crystals of [Ni(1,10-phenanthroline)CrO4•3H2O]•H2O, orange crystals of Ni(1,10-phenanthroline)3Cr2O7•3H2O, and yellow powdered Ni(1,10-phenanthroline)3Cr2O7•8H2O.[6]

References

  1. ISBN 9781439814628
    .
  2. ^ Eisler, R. (1998). Nickel Hazards to Fish, Wildlife, and Invertebrates: a Synoptic Review. Laurel: U.S. Geological Survey
  3. ^
    doi:10.1111/j.1151-2916.1968.tb15930.x
    .
  4. ^ Brandt, Karin (1943). "X-Ray Analysis of CrVO4 and isomorphous compounds". Arkiv för Kemi, Mineralogi och Geologi. 17A (6): 1–13. (not consulted)
  5. ^
    doi:10.1524/zkri.1969.130.1-6.112
    .
  6. ^
    doi:10.1016/S0277-5387(02)00912-9
    .
  7. S2CID 97516785
    .
  8. doi:10.1016/0584-8539(69)80133-9
    .
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