CRYSTAL-STRUCTURE AND EPR-SPECTRUM OF BISPYRIDINIUM BIS(CITRATO)CHROMIUM(III) TETRAHYDRATE

Citric acid reacts with chromium(VI) in aqueous solution leading to the formation of chromium(V), easily detectable by EPR. However, the redox reaction goes further with the formation of a chromium(III) citrate complex. This has been crystallized as the pyridinium salt and analysed by EPR and X-ray diffraction. The structure contains discrete Cr(Cit)2(2-) units, in which the chromium atom is octahedrally coordinated by two tridentate citrate anions. The anions and the solvate water molecules are linked by an extensive set of hydrogen bonds. The X-band and Q-band EPR spectra are well resolved, showing a large and highly anisotropic zero-field splitting.