title: Conformational analysis and vibrational circular dichroism of tris(ethylenediamine)ruthenium(II) complex: a theoretical study.
abstract: The conformational preferences and vibrational circular dichroism of tris(ethylenediamine)ruthenium complex in two main configurations (Lambda) and (Delta), have been performed using density functional theory. We find that for the free [Ru(en)(3)](2+) ion in the Delta-configuration, the conformational stability order is Delta(deltadeltadelta) > Delta(lambdadeltadelta) > Delta(lambdalambdadelta) > Delta(lambdalambdalambda) and that for the Lambda-configuration it is Lambda(deltadeltadelta) < Lambda(lambdadeltadelta) < Lambda(lambdalambdadelta) < Lambda(lambdalambdalambda). The energy differences between the four conformers for both the configurations Delta and Lambda are relatively small, but the activation barriers for ring inversion from one conformation to another are significant, as compared to other such systems. We trace the origin of these results to the lower oxidation state of Ru and relatively larger Ru-N bond length. We have also studied the effect of counterions on the conformational stability for Ru(en)(3)Cl(2.) Our results indicate a reverse stability order for the associated complex, Ru(en)(3) Cl(2) and higher activation barriers for ring inversion as compared to the free complex ion Ru(en)(3)(2+). It is because of larger hydrogen bonding interactions between the three N-H bonds and the chloride ion in these two conformers as compared to other conformations, which is also evident from the VCD spectra of N-H stretching modes. We also investigate IR spectra for all conformations in Delta- and Lambda-configurations and together with energetics and VCD spectra elucidate the spectroscopic characteristics of Ru(en)(3)(2+) complexes with and without the associated counterions.
authors.affiliation: Department of Chemistry, University of Kashmir, Srinagar, Kashmir, India.
authors.forename: Altaf Hussain
authors.initials: AH
authors.lastname: Pandith
authors.forename: Swapan K
authors.initials: SK
authors.lastname: Pati
mesh_terms: D002942:Circular Dichroism; D003198:Computer Simulation; D005029:Ethylenediamines / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D014732:Vibration
chemical_list: D005029:Ethylenediamines; D009942:Organometallic Compounds; D012428:Ruthenium