Nickel(II) chromate is an inorganic compound with the chemical formula (NiCrO<sub>4</sub>). It is red-brown in color and has a high heat tolerance. It is very slightly soluble in water and soluble in acid. It and the ions that compose it (nickel(II) and chromate) have been linked to tumor formation and gene mutation, particularly to wildlife.
Nickel(II) chromate can be formed in the lab by heating a mixture of chromium(III) oxide and nickel oxide at between 700 ðC and 800 ðC under oxygen at 1000 atm pressure. It can be produced at 535 ðC and 7.3 bar oxygen, but the reaction takes days to complete. If the pressure is too low or temperature too high but above 660 ðC, then the nickel chromium spinel NiCr<sub>2</sub>O<sub>4</sub> forms instead.
It is claimed it can be made using a hydrothermal technique.
Precipitates of Ni<sup>2+</sup> ions with chromate produce a brown substance that contains water.
The structure of nickel chromate is the same as for chromium vanadate, CrVO<sub>4</sub>. Crystals have an orthorhombic structure with unit cell sizes a = 5.482 ÃÂ , b = 8.237 ÃÂ , c = 6.147 ÃÂ . The cell volume is 277.6 ÃÂ <sup>3</sup> with four formula per unit cell.
Nickel chromate is dark in color, unlike most other chromates which are yellow. The infrared spectrum of nickel chromate show two sets of absorption bands. The first includes lines at 925, 825, and 800 cm<sup>âÂÂ1</sup> 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<sup>âÂÂ1</sup> produced from Ni-O stretching.
When heated at lower oxygen pressure around 600 ðC, nickel chromate decomposes to the nickel chromite spinel, nickel oxide and oxygen.
Nickel chromates can also crystallize with ligands. For instance, with 1,10-phenanthroline it can form: