Magnetic Anisotropy in Pentacoordinate Ni^II and Co^II Complexes: Unraveling Electronic and Geometrical Contributions

Abstract

The magnetic properties of the pentacoordinate [M (Me cyclam)N ] (Me cyclam=tetramethylcyclam; N =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 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 direction perpendicular to the Ni(Me cyclam) mean plane, whereas for M=Co it lies in the Co(Me cyclam) mean plane and thus perpendicular to the Co-N 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 (NCH) ] and [Co (NCH) ] 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 cyclam macrocycle. Moreover, the orientation of the anisotropy axes is mainly dependent on the geometry of the complexes.

From Heptacoordinated CrIII Complexes with Cyanide or Isothiocyanate Apical Groups to 1D Heterometallic Assemblages with All‐Pentagonal‐Bipyramid Coordination Geometries

“…The D value is consistent with positive parameters previously reported for Ni II square‐pyramidal complexes. [3c], The ferromagnetic Cr–Ni interaction in 9 lies within the range observed for Cr III and Ni II spin carriers bridged by cyanides …”

A Bis‐Binuclear NiII Complex with Easy and Hard Axes of Magnetization: Complementary Experimental and Theoretical Insights

“…It is important to note that T1 and T2 are very close in energy, whereas T3 is much higher (Table ). This energy spectrum is similar to that of Ni II in our recently reported complex [Ni(Me 4 cyclam)N 3 ] + , in which Ni II lies in a square‐pyramidal (spy) environment . Ni2 has its longest bond length with the oxygen atom belonging to the nitrate bridging the two binuclear complexes (Table ); it thus behaves from an electronic point of view as if it had a spy geometry with its hard anisotropy axis along the principal axis of the spy, as for [Ni(Me 4 cyclam)N 3 ] + .…”

Magnetic Anisotropy Switch: Easy Axis to Easy Plane Conversion and Vice Versa

“…Crystal Indexing : The crystals, of mass 57, 174, and 63 µg ( Tb , Ho , and Er , respectively), were indexed using a method previously described on a Single Crystal diffractometer Xcalibur3 with a Mo source (Kα, λ = 0.71 Å). Xcalibur3 is a 4 cycles kappa geometry diffractometer equipped with a Sapphire 3 CCD detector.…”