Experimental and theoretical charge density distribution in two ternary cobalt(III) complexes of aromatic amino acids

Overgaard, J; Waller, MP; Piltz, RO; Platts, JA; Emseis, P; Leverett, P; Williams, PA; Hibbs, DE

Experimental and theoretical charge density distribution in two ternary cobalt(III) complexes of aromatic amino acids

Date

2007-10-11

Authors

Publisher

American Chemical Society

Abstract

The experimental charge density distributions in two optically active isomers of a Co complex have been determined. The complexes are Δ-α-[Co(R,R-picchxn)(R-trp)](ClO4)(2)center dot H2O) (1) and Λ-β(1)-[Co(R,R-picchxn)(R-trp)](CF3SO3)(2)) (2), where picchxn is N,N '-bis(2-picolyl-1,2-diaminocyclohexane) and R-trp is the R-tryptophane anion. The molecular geometries of 1 and 2 are distinguished by the presence in complex 1 of intramolecular pi center dot center dot center dot pi stacking interactions and the presence in complex 2 of intramolecular hydrogen bonding. This pair of isomers therefore serves as an excellent model for studying noncovalent interactions and their effects on structure and electron density and the transferability of electron density properties between closely related molecules. For complex 2, a combination of X-ray and neutron diffraction data created the basis for a X-N charge density refinement. A topological analysis of the resulting density distribution using the atoms in molecules methodology is presented along with,d-orbital populations, showing that the metal-ligand bonds are relatively unaltered by the geometry changes between 1 and 2. The experimental density has been supplemented by quantum chemical calculations on the cobalt complex cations: close agreement between theory and experiment is found in all cases. The energetics of the weak interactions are analyzed using both theory and experiment showing excellent quantitative agreement. In particular it is found that both methods correctly predict the stability of 2 over 1. The transferability between isomers of the charge density and derived parameters is investigated and found to be invalid for these structurally related systems. © 2007, American Chemical Society

Keywords

Electron density, Molecules, Metals, X-ray diffraction, Resolution, Hydrogen, Molecular orbital method, Chemical bonds

Citation

Overgaard, J., Waller, M. P., Piltz, R., Platts, J. A., Emseis, P., Leverett, Williams, P. A., & Hibbs, D. E. (2007). Experimental and theoretical charge density distribution in two ternary cobalt(III) complexes of aromatic amino acids. Journal of Physical Chemistry A, 111(40), 10123-10133. doi:10.1021/jp068621n