The Relation between the Geometrical Configurations of Inorganic Complexes and their Absorption Bands. III. A General Rule for the First and Second Bands of Co (III) Complexes

A survey of the absorption data of the tetrammine- or bisethylenediamine-Co(III) complexes available in previous literature as well as in the author’s measurements has shown that the frequency differences of the first bands (or second bands) of the cis- and trans-isomers are closely related to the spectrochemical series of the ligands which coördinated in cis- or trans-positions. This correlation has been interpreted as the result of a trans-influence of the ligands, i.e., a trans-substitution causes a greater shift of the first band (or second band) than corresponding cis- substitution. The visible and ultraviolet absorption spectra of two isomers of [Co(NH3)4NO2·NCS]+ have been measured and the steric configurations of both ions have been determined.