Crystal and molecular structure and spectra of K4[Ni(NO2)6]·H2O and K3[Ni(NO2)4(O2N)]

Abstract

The crystal structure of the orange compound K₄[Ni(NO₂)₆]·H₂O has been determined. It shows that this contains an octahedral [Ni(NO₂)₆]^4– complex anion with six N-bonded nitrite ligands and a water of crystallization. Dehydration at 100 °C produces a mixture of red K₃[Ni(NO₂)₄(O₂N)] and KNO₂, with the latter occurring as microcrystallites ≈ 100 Å in size. Rehydration of the hygroscopic mixture at ≈ 20 °C causes K₄[Ni(NO₂)₆]·H₂O to be reformed. The nickel(II) in K₃[Ni(NO₂)₄(O₂N)] has a distorted octahedral ligand environment, with four nitrites co-ordinated via nitrogen, and a fifth chelating. The infrared and electronic spectra of the compounds are discussed in terms of the difference in nitrite co-ordination.