Structural characterization and conformational analysis of (aqua)(ethylenediamine-N,N,N′-triacetato)chromium(III) monohydrate complex. Crystal structure of the cis-equatorial isomer of [Cr(ed3a)(H2O)]·H2O

The structure of the cis-equatorial isomer of [Cr(ed3a)(H2O)]·H2O (ed3a=ethylenediamine-N,N,N′-triacetate ion) was determined by X-ray diffraction method. The complex crystallizes in the monoclinic space group P21/n, a=7.004(1) Å, b=15.958(2) Å, c=11.046(1) Å, β=97.16(1)°, and Z=4. Conformational analysis of the three possible geometrical isomers, trans(H2O,N′), trans(H2O,NH), and trans(H2O,O) of [Cr(ed3a)(H2O)] moiety, performed using the consistent force field (CFF) program with the recently developed parameters for EDTA-type complexes, yielded structural details and energies of the minimized form for each of the isomers. Calculated energies showed that the cis-eq isomer is the most stable one, with the geometry in a very good agreement with the crystallographic structure. Comparison of the molecular mechanics calculations with those for the analogous [Cr(ed3p)(H2O)]·H2O (ed3p=ethylenediamine-N,N,N′-tripropionate ion) revealed some general patterns for the conformational preference of EDTA-type complexes.