title: Six-coordinate Co(2+) with H(2)O and NH(3) ligands: which spin state is more stable?
abstract: Octahedral, six-coordinate Co(2+) can exist in two spin states. For biological ligands, H(2)O and NH(3), the most stable spin state is high spin (S = (3)/(2)). The difference in energy between high and low spin is dependent upon the ligand mix and coordination stereochemistry. High spin optimized geometries for these model compounds give structures close to octahedral symmetry. Low spin permits significant Jahn-Teller distortion. H(2)O ligands preferentially assume axial positions. Continuum solvent has a greater effect on low spin Co(2+), and it reduces the energy difference between the two spin states. For some ligand combinations optimized in the presence of solvent, there is no significant difference in energy between spin states.
authors.affiliation: Penn State University, Abington College, 1600 Woodland Road, Abongton, PA 19001, USA. ams@psu.edu
authors.forename: Ann M
authors.initials: AM
authors.lastname: Schmiedekamp
authors.forename: M Dominic
authors.initials: MD
authors.lastname: Ryan
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Deeth
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003035:Cobalt / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D007202:Indicators and Reagents; D008024:Ligands; D008956:Models, Chemical; D008968:Molecular Conformation; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D007202:Indicators and Reagents; D008024:Ligands; D000644:Quaternary Ammonium Compounds; D014867:Water; D003035:Cobalt