title: Tuning Magnetic Anisotropy Through Ligand Substitution in Five-Coordinate Co(II) Complexes.
abstract: Understanding the origin of magnetic anisotropy and having the ability to tune it are essential needs of the rapidly developing field of molecular magnetism. Such attempts at determining the origin of magnetic anisotropy and its tuning are still relatively infrequent. One candidate for such attempts are mononuclear Co(II) complexes, some of which have recently been shown to possess slow relaxation of their magnetization. In this contribution we present four different five-coordinated Co(II) complexes, 1-4, that contain two different "click" derived tetradentate tripodal ligands and either Cl-or NCS-as an additional, axial ligand. The geometric structures of all four complexes are very similar. Despite this, major differences are observed in their electronic structures and hence in their magnetic properties as well. A combination of temperature dependent susceptibility measurements and high-frequency and -field EPR (HFEPR) spectroscopy was used to accurately determine the magnetic properties of these complexes, expressed through the spin Hamiltonian parameters: g-values and zero-field splitting (ZFS) parameters D and E. A combination of optical d-d absorption spectra together with ligand field theory was used to determine the B and Dq values of the complexes. Additionally, state of the art quantum chemical calculations were applied to obtain bonding parameters and to determine the origin of magnetic anisotropy in 1-4. This combined approach showed that the D values in these complexes are in the range from -9 to +9 cm-1. Correlations have been drawn between the bonding nature of the ligands and the magnitude and sign of D. These results will thus have consequences for generating novel Co(II) complexes with tunable magnetic anisotropy and hence contribute to the field of molecular magnetism.
authors.affiliation: Institut für Chemie und Biochemie, Freie Universität Berlin , Fabeckstraße 34-36, D-14195 Berlin, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Schweinfurth
authors.affiliation: National High Magnetic Field Laboratory, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: J
authors.initials: J
authors.lastname: Krzystek
authors.affiliation: Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.|Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences , 1113 Sofia, Bulgaria.
authors.forename: Mihail
authors.initials: M
authors.lastname: Atanasov
authors.affiliation: Institut für Chemie und Biochemie, Freie Universität Berlin , Fabeckstraße 34-36, D-14195 Berlin, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Klein
authors.affiliation: Institut für Chemie und Biochemie, Freie Universität Berlin , Fabeckstraße 34-36, D-14195 Berlin, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Hohloch
authors.affiliation: Department of Biological, Chemical, and Physical Sciences, Roosevelt University , Chicago, Illinois 60605, United States.
authors.forename: Joshua
authors.identifier: http://orcid.org/0000-0003-3307-2556
authors.initials: J
authors.lastname: Telser
authors.affiliation: Universität Göttingen , Institut für Anorganische Chemie, Tammanstraße 4, D-37077 Göttingen, Germany.
authors.forename: Serhiy
authors.initials: S
authors.lastname: Demeshko
authors.affiliation: Universität Göttingen , Institut für Anorganische Chemie, Tammanstraße 4, D-37077 Göttingen, Germany.
authors.forename: Franc
authors.identifier: http://orcid.org/0000-0002-8613-7862
authors.initials: F
authors.lastname: Meyer
authors.affiliation: Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.affiliation: Institut für Chemie und Biochemie, Freie Universität Berlin , Fabeckstraße 34-36, D-14195 Berlin, Germany.
authors.forename: Biprajit
authors.identifier: http://orcid.org/0000-0003-4887-7277
authors.initials: B
authors.lastname: Sarkar