Complexes of meso- and dl-2,3-diaminobutane-N,N,N′,N′-tetraacetic acid with rare earth cations

Abstract

A spectrophotometric method is described by which the stabilities of 1 : 1 complexes of the coloured rare earth cations Pr 3+ and Nd 3+ with meso- and dl-2,3-diaminobutane-N,N,N′,N′-tetraacetic acid (DIMEDTA: H 4Y) can be determined. The proton affinities of each of these complexes is also reported. Spectrophotometric determinations of the position of equilibrium in the reaction Ln 3 + MY − ⇌ LnY − + M 3+ (where M = Pr or Nd and Ln is a colourless lanthanon) have been carried out and enable the stability constants of complexes of all the remaining lanthanons to be determined. All results are valid for 20·0°C and μ = 0·1 M (NaClO 4). The stability of the Cd 2+- meso-DIMEDTA complex was also measured by this procedure and the value (log K CdY = 16·74) compared with the results of spectrophotometric (16·86) polarographic (16·77) and potentiometric (16·59) procedures. The new data are discussed in terms of the possible stereochemistry of the complexes and the effect of steric hindrance by the methyl groups.