Rationalization of single-molecule magnet behavior in a three-coordinate Fe(iii) complex with a high-spin state (S= 5/2)

Abstract

A trigonal-planar Fe(iii) complex Fe[N(SiMe3)2]3 with a high spin state (S = 5/2) was investigated by magnetic and HF-EPR measurements, exhibiting distinct dynamic magnetic behaviour.

A “Solvent‐Free” Crystal Structure of [Fe{N(SiMe3)2}3] – Synthesis, Structure and Properties

“…The value of U eff is quite similar to the one obtained by Ge et al. ( U eff =6.91 cm −1 ) from ac measurements at H dc =1600 Oe on crystals obtained by crystallization from solution [39] . In contrast, the pre‐exponential factor for those crystals is higher by one order of magnitude ( τ 0 =3.85 ⋅ 10 −5 s −1 ) when compared with our data for the ‘solvent‐free’ crystals obtained by sublimation (In this context we note that most probably this number in literature is wrong by one order of magnitude and should read τ 0 =3.85 ⋅ 10 −6 s −1 fitting better to the graph and which would then mean a much better agreement with our results).…”

“…For comparison, we performed dc magnetic measurements of 1 , obtained by sublimation, between 2 and 300 K in a field of 0.1 T and magnetization measurements from 0 to 7 T at 2, 3, 4, 6, 10 and 25 K. Similar to the results of Ge et al. the values of χT display a clear deviation from the Curie law below 30 K and, in agreement, the shape of the magnetization curves indicates magnetic anisotropy (Figure S5 and Figure S6, ESI) [39] . However, fits of our data performed with the PHI program [40] lead to slightly different spin Hamiltonian (SH) parameters given and compared in Table 5 (satisfying fits could not be obtained with an isotropic g value).…”

“…The static and dynamic magnetic properties of 1 crystallized from toluene were published in a recent paper [39] . For comparison, we performed dc magnetic measurements of 1 , obtained by sublimation, between 2 and 300 K in a field of 0.1 T and magnetization measurements from 0 to 7 T at 2, 3, 4, 6, 10 and 25 K. Similar to the results of Ge et al.…”

Single‐Ion Magnetic Behaviour in an Iron(III) Porphyrin Complex: A Dichotomy Between High Spin and 5/2–3/2 Spin Admixture

“…A high‐spin 3d 5 complex should be magnetically isotropic ( D =0), but the proximity of the excited quartet ( S= 3/2) states, which depends on the ligand fields, can significantly affect the ground state, inducing anisotropy. Only recently, SIM behaviour (with D <0), was observed for S= 5/2 iron(III) compounds [58–60] . The ground state in iron(III) porphyrins in particular can be tuned by the ligand field, as observed in such complexes showing S= 1/2, 3/2, and 5/2 ground states, [34–36] including those with S= 5/2 and positive and sizable D values [61–63] .…”

Methods and Models of Theoretical Calculation for Single-Molecule Magnets

“…Moreover, the Fe(III) complexes without intermediate spin S = 3/2 show positive D values, while the existence of intervening spin S = 3/2 makes it possible to generate a large negative D value. Our group carried out a detailed study on Fe[N(SiMe 3 ) 2 ] 3 with perfect local D 3h symmetry to explore its magnetic anisotropy (Figure 4) [44]. Three classes of methods were performed to acquire D: least-square fitting toward data from high-frequency EPR (HF-EPR) and ab initio calculation and data fitting based on spin Hamiltonian.…”