Studies on Dimethylglyoximato cobalt (III) Complexes. II Absorption Spectra of Bis-(dimethylglyoximato)- and Bis-(mono-O-methyl-dimethylglyoximato)-cobalt (III) Complexes

Abstract Two new compounds, [Co(NH3)2(DCH3)2]Cl and H[Co(DCH3)2(NO2)2] have been synthesized as the first examples of tervalent-cobalt complexes of dimethylglyoxime-mono-methylether. Absorption spectra of the compounds and several bis-(dimethylglyoximato)-cobalt (III)-complexes in solution have been measured. The absorption curves of bis-(dimethylglyoximato)-cobalt (III)-complexes, generally, consist of three inflations and one maximum. The inflation in the visible region is the vestige of the first absorption band, and the two other inflations and one maximum in the ultraviolet region are the specific absorption bands which are due mainly to the dimethylglyoximate ions in coördination. As for the first absortion bands, the results of the measurements can successfully be elucidated on the basis of the spectrochemical- and hyperchromic-series found by Tsuchida et al. For NH4[Co(DH)2(NO2)2], is also the specific band originated from the nitro-groups in coördination remarkable. The isolated maxima on the curves of H[Co(DH)2Cl2] and H[Co(DH)2Br2] in the longer wave-length region are nothing but the first absorption bands which are shifted towards red owing to the bathochromic effect of the two halogenide ions. In the dibromo-complex, the third absorption band is conspicuous. It has never been recognized clearly in the other complexes with dimethylglyoxime. The absorption curves of bis-(mono-O-methyl-dimethylglyoximato)-complexes, as a whole, resemble those of corresponding dimethylglyoximato-complexes, but the bathochromic shift of the specific absorption bands from that of free ligand molecule amounts to a considerable degree in comparison with the cases of dimethylglyoximato-complexes. And this phenomenon is elucidated in connexion with the O-H-O hydrogen bonds. From comparison of the reactions for preparing the bis-(mono-O-methyl-dimethylglyoximato)- and bis-(dimethylglyoximato)-complexes, the high stability of the latter was discussed.