Isomer stabilities of tartrate-bridged binuclear complexes

Abstract

The seven possible isomers for a tetragonal coordination geometry and the twenty-four possible isomers for trigonal-bipyramidal and octahedral geometries are enumerated and described for binuclear tartrate-bridged complexes. Two geometrical parameters corresponding to the strain in the binuclear structure and to the ligand conformation energy have been evaluated as a function of the coordination geometry. Predictions of the relative energies of tartrate-bridged isomers made from these parameters agree with known stability differences when protonation of the tartrate ligand is also considered. An entropy factor of Rln2 contributes to the stabilities of the mixed-ligand isomers. This work indicates that tartrate-bridging may be used to induce known absolute configurations about metal ions for CD studies and for stereochemical correlations and to lock tartrate groups into known conformations for thermochemical determinations of conformational energies.