Ising-type Magnetic Anisotropy and Slow Relaxation of the Magnetization in Four-Coordinate Amido-Pyridine Fe^II Complexes

Abstract

A family of four-coordinate Fe complexes formed with N,N'-chelating amido-pyridine ligands was synthesized, and their magnetic properties were investigated. These distorted tetrahedral complexes exhibit significant magnetic anisotropy with zero-field splitting parameter D ranging between -17 and -12 cm. Ab initio calculations enabled identification of the structural factors that control the nature of the magnetic anisotropy and the rationalization of the variation of D in these complexes. It is shown that a reduced N-Fe-N angle involving the chelating nitrogen atoms of the ligands is at the origin of the negative D value and that the torsion between the two N-Fe-N planes imposed by steric hindrances further increases the |D| value. Field-induced slow relaxation of magnetization was observed for the three compounds, and a single-molecule magnet behavior with an energy barrier for magnetization flipping (U) of 27 cm could be evidenced for one of them.

Role of Coordination Number and Geometry in Controlling the Magnetic Anisotropy in FeII, CoII, and NiII Single‐Ion Magnets

“…have studied three four‐coordinate complexes, of which [Fe(N2mes) 2 ] complex ( 65 ) (where N2mes=2‐[mesitylamino)methyl]pyridine) exhibited a D value of −13.7 cm −1 (from NEVPT2 calculations) with U eff =27 cm −1 (see Table 2). [64] …”

Magnetic Anisotropy and Field‐induced Slow Relaxation of Magnetization in Tetracoordinate CoII Compound [Co(CH3‐im)2Cl2]

“…Nevertheless, if we consider a special category of SMMs with one paramagnetic center, so called single-ion magnets (SIMs), then the deliberate modulation of the magnetic anisotropy is easier and depends reasonably on the topology and donor atom constitution of the coordination polyhedron [2]. Up to now, several correlations on the relationship between a structure and anisotropy parameters have been reported, namely for tetracoordinate [8,9], pentacoordinate [10,11], hexacoordinate Ni II and Co II compounds [12,13], tetracoordinate Fe II compounds [14] and penta and hexacoordinate Mn III compounds [15,16]. From these, the largest number of complexes exhibiting slow-relaxation of magnetization belongs undoubtedly to the group of tetracoordinate Co II compounds, which we have chosen as an object of the present study.…”

Study of the Electronic Structure of NiGa2S4 and Extraction of the Spin Hamiltonian Parameters from Ab Initio Calculations

“…From this identification, both the relevant operators and the values of their corresponding interactions can be determined rigorously and univocally. Such a procedure has been used successfully to extract subtle interactions such as electron transfer, Coulomb repulsion, isotropic magnetic coupling, zero‐field splitting (ZFS) parameters, double exchange interactions, exchange transfer terms,, , and three‐ and four‐body terms , …”