Hexadentate chromium(III) complexes containing unsymmetrical edta-type ligands

Abstract Structural data are given for two recently reported hexadentate chromium(III) complexes: trans(O5)-Na[Cr(ed3ap)]·3H2O (A) and Na[Cr(u-eddadp)]·3H2O (B) (ed3ap=ethylenediamine-N,N,N′-triacetate-N′-3-propionate ion; u-eddadp=ethylenediamine-N-diacetate-N′-di-3-propionate ion). Only one, the favored (trans(O5)) isomer of the complex A was resolved. Also, the complex A was found to be spontaneously resolved. The absolute configuration around the chromium(III) ion in the crystal A has been determined to be Λ(ΛΔΛ). The complexes crystallize in the space group P212121 (for A) and Pna21 (for B) of the orthorhombic crystal system. Final R values are 0.045 for A and 0.078 for B. The conformations of the chelate rings are found to be the envelope for the glycinate rings (R relatively flat and G with a significant deviation) and distorted skew-boat (half-chair) for the β-alaninate rings. Structural parameters and strain analysis data of complexes A and B and related [Cr(edta-type)]− chelates are compared and discussed in relation to the structure of the ligand and octahedral distortion of complexes. The CD spectra of the Λ-(−)589-trans(O5)-[Cr(ed3ap)]− (A) and the other edta-type Cr(III) complexes have been correlated and discussed.