Chromium(II) chemistry. Part IX. Ferromagnetic and antiferro-magnetic chlorochromates(II)

Abstract

The new chromium(II) complex chlorides M₂[CrCl₄(OH₂)₂][M = NH₄, Hpy (pyridiniurm). Rb,orCs] are magnetically dilute, high-spin compounds with reflectance spectra of the type expected for tetragonally distorted octahedral anions [CrCl₄(OH₂)₂]^2–. Several compounds are isomorphous with their copper(II) analogues of known structure. Thermal dehydration gives compounds M₂[CrCl₄](M = NH₄, Rb, or Cs), which are ferromagnetic as is K₂[CrCl₄] obtained from a hydrate too unstable to be completely characterized. The reflectance spectra again indicate tetragonal six-co-ordination, and hence the anhydrous compounds have polymeric structures which permit the ferromagnetic interaction through 180° coupling. Unusually intense spin-forbidden absorptions are found in the reflectance spectra of these compounds. The complex Cs[CrCl₃(OH₂)₂] is weakly antiferromagnetic and presumably has a similar structure to Li[CuCl₃(OH₂)₂]. Chloride-bridged structures in [Hpy]₂[CrCl₄] and M[CrCl₃](M = Hpy, Me₄N, or Cs) produce antiferromagnetic behaviour which leads to slight intensification of the spin-forbidden bands.