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Magnetic Anisotropy in Pentacoordinate Ni II and Co II Complexes: Unraveling Electronic and Geometrical Contributions
Author(s) -
Cahier Benjamin,
Perfetti Mauro,
Zakhia Georges,
Naoufal Daoud,
ElKhatib Fatima,
Guillot Régis,
Rivière Eric,
Sessoli Roberta,
Barra AnneLaure,
Guihéry Nathalie,
Mallah Talal
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201604872
Subject(s) - cyclam , anisotropy , magnetic anisotropy , chemistry , magnetization , crystallography , coordination geometry , geometry , condensed matter physics , magnetic field , metal , physics , molecule , optics , hydrogen bond , mathematics , organic chemistry , quantum mechanics
The magnetic properties of the pentacoordinate [M II (Me 4 cyclam)N 3 ] + (Me 4 cyclam=tetramethylcyclam; N 3 =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 −1 for 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−N azido direction perpendicular to the Ni(Me 4 cyclam) mean plane, whereas for M=Co it lies in the Co(Me 4 cyclam) mean plane and thus perpendicular to the Co−N azido direction. 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 [Ni II (NCH) 5 ] 2+ and [Co II (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 Me 4 cyclam macrocycle. Moreover, the orientation of the anisotropy axes is mainly dependent on the geometry of the complexes.