The chemistry of chromium(V): the preparation and properties of tetra-chlorobis(ethanoic acid)chromates(III) and related complexes

Abstract

The preparations and characterisation of the chromium(V) species [A][CrOCl₄](A = pyridinium, quinolinium, isoquinolinium, NMe₄, NEt₄, or AsPh₄). [H₂B][CrOCl₅](B = 2,2′- or 4,4′-blpyridine), and Cs₂[CrOCl₅] are described, and their i.r. and electronic spectra are reported. The two lowest-energy bands in the electronic spectra of [A][CrOCl₄](ca. 13 000 and 18 000 cm^–1) are assigned to d_xy→d_xz,yz and Cr–O(π)→ Cr–O(σ*) transitions, respectively. The experimental data are incompatible with the energy of the band at 18 000 cm^–1 being equated with 10Dq for the in-plane ligands. A recently reported preparation of [H₂–2,2′-bipy][CrOBr₅] is shown to be non-repeatable. A novel series of chromium(III) complexes, containing the anions [CrX₄-(HO₂CMe)₂]^– and [CrX₅(HO₂CMe)]^2–(X = Cl or Br), has also been prepared, and these undergo ligand-exchange reactions to form complexes containing the anions [CrCl₄(NCMe)₂]^– and [CrCl₅(NCMe)]^2–.