The ion-exchange chromatographic separation of the components of the product mixture resulting from reaction of trans-dichlorobis (ethylenediamine) cobalt (III) chloride with thiocyanate ion

摘要

The object of the research was to study, by means of ion-exchange chromatography, the product mixture resulting from reaction of trans-[Co(en)₂Cl₂]Cl and SCN¬⁻. Cis-and trans-[Co(en)₂(NCS)Cl]Cl had previously been obtained as products of this reaction. However, the possibility of the presence of other products consistent with the nature of the reactants could not be dismissed. These include the dichlora, dithiocyanato, and aqua complexes. The constituents of the solution resulting from the reaction were separated on a column of Dowex 50W-X8 resin by elution with hydrochloric acid. The eluted fractions were evaporated at room temperature in order to obtain crysta1s to be used for infrared spectral analysis and identification. Three primary fractions were eluted from the column. The first, eluted with 0.5 M HCl, was identified as trans-[Co(en)₂(NCS)Cl]Cl by analysis of the infrared spectrum. Two types of crystals were obtained from the second fraction which was eluted with 1 M HCL. The first crystals to form in this solution were orange in color and were identified by examination of the infrared spectrum as cis-[Co(en)₂(NCS)Cl]Cl. The second crystals obtained from the same fraction were shown to be cis-[Co(en)₂(NCS)Cl]Cl. The crystals isolated from the third fraction, eluted with 3 M¬¬ HCl, were also identified as cis [Co(en)₂(NCS) Cl]Cl. On the basis of observations of the column elution and an analysis of the ultraviolet spectra of’ the eluted fractions, it was concluded that band #2 was cis-[Co(en)₂(NCS)Cl] Cl and band #3 was cis-[Co(en)₂(NCS)(H₂0)]Cl₂. Aquation of cis-[Co(en)₂(NCS)Cl]⁺ was observed to occur on the column as well as in the eluted solution. In addition, rechlorination of the aquated compound was found to occur in the eluted fraction so that after elution the second and third fractions were mixtures of the unaquated and aquated complexes. No crystals of dithiocyanato or dichloro compounds were obtained in the separation so that the reaction was demonstrated to be essentially1:1 between the complex and thiocyanate. Trans-[Co(en)₂(NCS)Cl]Cl was found to comprise forty-nine percent of the typical product mixture. Since other products were present only in very low concentrations, the combined cis-[Co(en)₂(NCS)Cl]Cl and cis-[Co(en)₂(NCS)(H₂0)]Cl₂ contents was estimated at roughly fifty mole percent.