Conformational analysis of edta-type rhodium(III) complexes with mixed five- and six-membered chelate rings. Structural analysis of conformational flexibility in rhodium(III) complexes containing 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate liga

Conformational analysis of the three possible geometrical isomers: trans(O5), trans(O5O6) and trans(O6) of the sexidentate [Rh(1,3-pddadp)]− complex, and of the 10 possible isomers: four cis-equatorial, four cis-polar and two trans-equatorial of the quinquedentate [Rh(1,3-pddadp)Cl]2− complex was performed using the consistent force field (CFF) method, with the parameters developed previously for edta-type complexes of chromium(III) and supplemented with new parameters for rhodium(III). The force field is of maximally diagonal type. The energy-minimized structure of the cis-polar,trans(Cl,O5) isomer, having the same absolute configuration at the nitrogen atoms and 5-6-6 ring system in the G plane, represents the global minimum for the quinquedentate [Rh(1,3-pddadp)Cl]2− species. In the case of sexidentate [Rh(1,3-pddadp)]− complex the lowest energy conformer corresponds to the trans(O5O6) configuration. CFF calculations reproduced very well all crystallographically characterized structures: trans(O5)-[Rh(1,3-pddadp)]−, trans(O5O6)-[Rh(1,3-pddadp)]− and cis-polar,trans(Cl,O5)-[Rh(1,3-pddadp)Cl]2−. Comparison of the present molecular mechanics results with those for the analogous complexes revealed some general patterns for the conformational preferences of edta-type complexes.