Nickel(II) chromate

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]

Nickel chromate

Names
IUPAC name Nickel(II) chromate
Other names nickelous chromate nickel chromate nickel(II) chromium(VI) oxide
Identifiers
CAS Number	14721-18-7 N
3D model (JSmol)	Interactive image
ChemSpider	55656 N
ECHA InfoCard	100.035.227
EC Number	238-766-5
PubChem CID	61767
CompTox Dashboard (EPA)	DTXSID201027437
InChI InChI=1S/Cr.Ni.4O/q;+2;;;2*-1 Key: QGAXAFUJMMYEPE-UHFFFAOYSA-N
SMILES [O-][Cr](=O)(=O)[O-].[Ni+2]
Properties
Chemical formula	NiCrO4
Molar mass	174.71 g/mol
Appearance	dark maroon-colored powder
Solubility in water	very slightly soluble in water[1]
Solubility	soluble in hydrochloric acid
Hazards
Flash point	Non-flammable
Related compounds
Other anions	nickel(II) molybdate 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). N verify (what is YN ?) Infobox references

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)

Related

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]