HETEROBINUCLEAR CHELATES OF SOME TRANSITION-METAL IONS WITH CHROMIUM(III) DIETHYLENETRIAMINEPENTAACETATO COMPLEX

The reactions of chromium(III)-DTPA ''chelating agent'' with manganese (II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) have b een investigated in aqueous solution by potentiometric methods. The he terobinuclear chelates with 1:1:1 metal(II):chromium-(III):DTPA molar ratio have been precipitated and characterized by spectroscopic and th ermoanalytical techniques. All the metal ions are six-coordinated with an octahedral configuration (except the four-coordinated copper(II)) and are covalently bound to the free iminodiacetic group of the chromi um(III)-DTPA complex. The thermal stability depends on the furnace atm osphere (N2 or O2), whereas the nature of the metal(II) ion is less im portant because the anhydrous complexes begin to decompose at about th e same temperature. Exceptions to this rule are the copper(II) and iro n(II) complexes, which are less stable.