A 7-COORDINATE STRUCTURE OF IRON(II)-ETHYLENEDIAMINE-N,N,N',N'-TETRAACETATO COMPLEX AS DETERMINED BY X-RAY CRYSTAL ANALYSIS

A single-crystal X-ray analysis has revealed that the Fe(II)-edta complex, formulated as Na2[Fe(edta)(H2O)].2NaClO4.6H2O, has a seven-coordinate structure close to a mono-capped trigonal prism (C2v-CTP). The crystal data axe as follows: Orthorhombic, Pmnb, a=11.404(1), b=23.573(2), c=9.915(1) angstrom, and Z=4. In the complex anion, edta serves as a hexadentate ligand with its two N atoms at a unique edge and four 0 atoms at the corners of a quadrilateral face, which is capped with a water molecule. The presence of the labile water molecule in the first coordination sphere accounts for the kinetic lability of the Fe(II)-edta complex, which has been frequently pointed out. A qualitative comparison of the molecular structures was made between the seven-coordinate Fe(II)- and Fe(II)-edta complex anions. The steric and electronic requirements for seven-coordination are also discussed concerning the transition-metal edta complexes.