Structural and theoretical investigations of the Rh(III) and Co(III) complexes containing symmetrical edta-type ligands with mixed carboxylate and diamine rings: Quantum-mechanical/NBO insight into stability of geometrical isomers

摘要

The trans(O5O6) isomer of the Na[Rh(eddadp)]center dot 4H(2)O and the K[Co(eddadp)]center dot 3H(2)O (eddadp = ethylenediamine-N,N'-diacetate-N,N'-di-3-propionate) were synthesized and Na[Rh(eddadp)]center dot 4H(2)O structure was confirmed by X-ray diffraction analysis. The percentage of particular isomers found in reaction equilibrium mixtures of [M(eddadp)](-) complex has been reported. Single crystal X-ray diffraction of the complex revealed an octahedral geometry of the Rh(III) centre. Improved structural distortion analysis of M(III) (M = Rh, Co) complexes with symmetric edta-type of ligands containing mixed carboxylate and diamine rings was made. Structural distortion analysis has determined high values of total deviation of the octahedral angles (Delta(O-h)) for both existing trans(O-5) (34 degrees) and trans(O5O6) (41 degrees) isomers of [Rh (eddadp)](-) complex, while in the case of a similar Co(III) complex, relatively low value (31 degrees) for trans (O-5) has been established. Extensive QM/NBO calculations were made for both systems [M(eddadp)](-) and [M(1,3-pddadp)](-) using different DFT methods (B3LYP/SDD, M06/SDD, MP2/SDD). By correlating the structural parameters obtained from X-ray and DFT optimized 3D structures, the B3LYP/SDD method was used as the method of choice. Based on the correlation between the energies of the optimized systems and the strain parameters, the existence of the trans(O-6) isomer of the [Rh(1,3-pddadp)](-) complex was predicted. NRT (Natural Resonance Theory) analysis gave the best resonances for each isomer. Here the stability of particular isomer has been described in terms of 3-CHB bonds involving metal ions and Second Order Perturbation Theory analysis using Donor/Acceptor energies. Further, to explain the bonding nature of M-edta-type complexes the Natural Coulomb Electrostatics (NCE) analysis has been done as well. The pairwise steric exchange interaction E-I,J(WX) results obtained for the best-ranked resonances of dif