title: Magnetic Anisotropy in Pentacoordinate NiIIand CoIIComplexes: Unraveling Electronic and Geometrical Contributions.
abstract: The magnetic properties of the pentacoordinate [MII(Me4cyclam)N3]+(Me4cyclam=tetramethylcyclam; N3=azido; M=Ni, Co) complexes were investigated. Magnetization and EPR studies indicate that they have an easy plane of magnetization with axial anisotropy parameters D close to 22 and greater than 30 cm-1for the Ni and Co complexes, respectively. Ab initio calculations reproduced the experimental values of the zero-field splitting parameters and allowed the orientation of the anisotropy tensor axes with respect to the molecular frame to be determined. For M=Ni, the principal anisotropy axis lies along the Ni-Nazidodirection perpendicular to the Ni(Me4cyclam) mean plane, whereas for M=Co it lies in the Co(Me4cyclam) mean plane and thus perpendicular to the Co-Nazidodirection. These orientations match one of the possible solutions experimentally provided by single-crystal cantilever torque magnetometry. To rationalize the geometry and its impact on the orientation of the anisotropy tensor axis, calculations were carried out on model complexes [NiII(NCH)5]2+and [CoII(NCH)5]2+by varying the geometry between square pyramidal and trigonal bipyramidal. The geometry of the complexes was found to be the result of a compromise between the electronic configuration of the metal ion and the structure-orienting effect of the Me4cyclam macrocycle. Moreover, the orientation of the anisotropy axes is mainly dependent on the geometry of the complexes.
authors.affiliation: Institut de Chimie Moléculaire et des Matériaux O'Orsay, CNRS, Université Paris Sud 11, Université Paris Saclay, 91405, Orsay Cedex, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Cahier
authors.affiliation: Dipartimento di Chimica "U. Schiff", Università degli studi di Firenze & INSTM UdR Firenze, Via della Lastruccia 3-13, 50019, Sesto Fiorentino, Italy.|Universität Stuttgart, Institut für Physikalische Chemie, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Mauro
authors.initials: M
authors.lastname: Perfetti
authors.affiliation: Institut de Chimie Moléculaire et des Matériaux O'Orsay, CNRS, Université Paris Sud 11, Université Paris Saclay, 91405, Orsay Cedex, France.
authors.forename: Georges
authors.initials: G
authors.lastname: Zakhia
authors.affiliation: Laboratoire de Chimie de Coordination Inorganique et Organométallique, LCIO, Université Libanaise, Faculté des Sciences I, Hadath, Lebanon.
authors.forename: Daoud
authors.initials: D
authors.lastname: Naoufal
authors.affiliation: Institut de Chimie Moléculaire et des Matériaux O'Orsay, CNRS, Université Paris Sud 11, Université Paris Saclay, 91405, Orsay Cedex, France.
authors.forename: Fatima
authors.initials: F
authors.lastname: El-Khatib
authors.affiliation: Institut de Chimie Moléculaire et des Matériaux O'Orsay, CNRS, Université Paris Sud 11, Université Paris Saclay, 91405, Orsay Cedex, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Guillot
authors.affiliation: Institut de Chimie Moléculaire et des Matériaux O'Orsay, CNRS, Université Paris Sud 11, Université Paris Saclay, 91405, Orsay Cedex, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Rivière
authors.affiliation: Dipartimento di Chimica "U. Schiff", Università degli studi di Firenze & INSTM UdR Firenze, Via della Lastruccia 3-13, 50019, Sesto Fiorentino, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Sessoli
authors.affiliation: Laboratoire National des Champs Magnétiques Intenses, UPR CNRS 3228, Université J. Fourier, 25, avenue des Martyrs, B.P. 166, 38042, Grenoble Cedex 9, France.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Barra
authors.affiliation: Laboratoire de Chimie et Physique Quantiques, Université de Toulouse III, 118, route de Narbonne, 31062, Toulouse, France.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Guihéry
authors.affiliation: Institut de Chimie Moléculaire et des Matériaux O'Orsay, CNRS, Université Paris Sud 11, Université Paris Saclay, 91405, Orsay Cedex, France.
authors.forename: Talal
authors.identifier: http://orcid.org/0000-0002-9311-3463
authors.initials: T
authors.lastname: Mallah
keywords: EPR spectroscopy; ab initio calculations; cobalt; magnetic properties; nickel