Absorption Spectra of Co-ordination Compounds. III. Special Bands of Chromium Complexes

(1) Absorption spectra of several chromic complexes were measured and it was found that the spectrochemical series is coincident with that for cobaltic complexes.(2) From the spectrochemical series was discussed the stability of the chromic complexes and some of the methods of preparation were explained.(3) All the chromic complexes have the first and the second bands. [Cr(NH3)5NCS] (NCS)2has another band in addition, which is due to the group M←N=C (M= a metal-ion of any kind and valency). [Cr(NH3)2(NCS)4]NH4and [Cr(NCS)6]K3have four bands each, the first, the second, the special and the third. The special bands are due to the same origin as that of [Cr(NH3)5NCS]X2and the third bands are attributed to trans-pairing of the anions.(4) Chromate ion, a quadri-coördinate complex, has not the first band, but the second and the third, as could be expected from the author’s hypotheses.(5) Absorption spectra of polynuclear compounds may be analysed into those of component complex radicals. For example [Co(NH3)5CrO4]Cl has three bands, of which one is the first band of the sexa-coördinate cobaltic complex and the other two are mainly the second and the third band of quadri-coördinate chromate radical. The second band of the former is almost entirely covered by the second band of the latter.