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)]center dot 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 P2(1)/n, a = 7.004(l) Angstrom, b = 15.958(2) Angstrom, c = 11.046(l) Angstrom, beta = 97.16(l)degrees , and Z = 4. Conformational analysis of the three possible geometrical isomers, trans(H2O,N'), trans(H2O,N-H), 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. (C) 2003 Elsevier B.V. All rights reserved