title: Origin of the Zero-Field Splitting in Mononuclear Octahedral Mn(IV) Complexes: A Combined Experimental and Theoretical Investigation.
abstract: The aim of this work was to determine and understand the origin of the electronic properties of Mn(IV) complexes, especially the zero-field splitting (ZFS), through a combined experimental and theoretical investigation on five well-characterized mononuclear octahedral Mn(IV) compounds, with various coordination spheres (N6, N3O3, N2O4 in both trans (trans-N2O4) and cis configurations (cis-N2O4) and O4S2). High-frequency and -field EPR (HFEPR) spectroscopy has been applied to determine the ZFS parameters of two of these compounds, MnL(trans-N2O4) and MnL(O4S2). While at X-band EPR, the axial-component of the ZFS tensor, D, was estimated to be +0.47 cm(-1) for MnL(O4S2), and a D-value of +2.289(5) cm(-1) was determined by HFEPR, which is the largest D-magnitude ever measured for a Mn(IV) complex. A moderate D value of -0.997(6) cm(-1) has been found for MnL(trans-N2O4). Quantum chemical calculations based on two theoretical frameworks (the Density Functional Theory based on a coupled perturbed approach (CP-DFT) and the hybrid Ligand-Field DFT (LF-DFT)) have been performed to define appropriate methodologies to calculate the ZFS tensor for Mn(IV) centers, to predict the orientation of the magnetic axes with respect to the molecular ones, and to define and quantify the physical origin of the different contributions to the ZFS. Except in the case of MnL(trans-N2O4), the experimental and calculated D values are in good agreement, and the sign of D is well predicted, LF-DFT being more satisfactory than CP-DFT. The calculations performed on MnL(cis-N2O4) are consistent with the orientation of the principal anisotropic axis determined by single-crystal EPR, validating the calculated ZFS tensor orientation. The different contributions to D were analyzed demonstrating that the d-d transitions mainly govern D in Mn(IV) ion. However, a deep analysis evidences that many factors enter into the game, explaining why no obvious magnetostructural correlations can be drawn in this series of Mn(IV) complexes.
authors.affiliation: Center for Chemistry, Institute of Chemistry, Technology and Metallurgy, University of Belgrade , Njegoševa 12, P.O. Box 815, 11001 Belgrade, Serbia.
authors.forename: Matija
authors.initials: M
authors.lastname: Zlatar
authors.affiliation: Faculty of Chemistry, University of Belgrade , Studentski trg 12-16, 11001 Belgrade, Serbia.
authors.forename: Maja
authors.initials: M
authors.lastname: Gruden
authors.affiliation: Department of Chemistry, Taras Shevchenko National University of Kyiv , 64/13 Volodymyrska str., Kyiv 01601, Ukraine.
authors.forename: Olga Yu
authors.initials: OY
authors.lastname: Vassilyeva
authors.affiliation: Department of Chemistry, Taras Shevchenko National University of Kyiv , 64/13 Volodymyrska str., Kyiv 01601, Ukraine.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Buvaylo
authors.affiliation: Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf (HZDR), D-01328 Dresden, Saxony, Germany.
authors.forename: A N
authors.initials: AN
authors.lastname: Ponomarev
authors.affiliation: Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf (HZDR), D-01328 Dresden, Saxony, Germany.
authors.forename: S A
authors.initials: SA
authors.lastname: Zvyagin
authors.affiliation: Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf (HZDR), D-01328 Dresden, Saxony, Germany.|Institut für Festkörperphysik, Technische Universität Dresden , D-01062 Dresden, Saxony, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Wosnitza
authors.affiliation: National High Magnetic Field Laboratory (NHMFL), Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: J
authors.initials: J
authors.lastname: Krzystek
authors.affiliation: Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria , Avenida de los Castros s/n, 39005 Santander, Cantabria, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Garcia-Fernandez
authors.affiliation: Département de Chimie Moléculaire, Université Grenoble Alpes/CNRS, UMR-5250 , BP-53, 38041 Grenoble Cedex 9, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Duboc