A physicochemical study of chromium(III) mononuclear, dinuclear and heteronuclear chelates of triethylenetetraaminehexaacetic acid.

The existence of mononuclear and dinuclear chromium(III) chelates of triethylenetetraaminehexa-acetic acid (ttha) in aqueous solution has been demonstrated by potentiometric pH titration and electronic visible spectroscopy. The isolation of mononuclear, dinuclear and heteronuclear chromium(III) chelates of ttha has been accomplished. Magnetic susceptibility measurements on the isolated solids point to the absence of magnetic exchange coupling in the dinuclear chromium(III) chelate and in the heteronuclear chelate containing chromium(III) and copper(II). However, the differences in the e.s.r. spectra of the mononuclear and dinuclear ttha chelates observed in frozen aqueous solution may arise from some form of magnetic dipolar coupling between the chromium(III) ions in the dinuclear chelate.