Heterobinuclear chelates of some transition metal ions with chromium(III)—diethylenetriaminepentaacetato complex

Abstract: The reactions of chromium(III)-DTPA ''chelating agent'' with manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) have been investigated in aqueous solution by potentiometric methods. The heterobinuclear chelates with 1:1:1 metal(II):chromium-(III):DTPA molar ratio have been precipitated and characterized by spectroscopic and thermoanalytical 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 chromium(III)-DTPA complex. The thermal stability depends on the furnace atmosphere (N2 or O2), whereas the nature of the metal(II) ion is less important because the anhydrous complexes begin to decompose at about the same temperature. Exceptions to this rule are the copper(II) and iron(II) complexes, which are less stable.