Slow magnetic relaxation in structurally similar mononuclear 8-coordinate Fe(ii) and Fe(iii) compounds

Abstract

A pair of structurally-similar and stable 8-coordinate high-spin Fe(ii) and Fe(iii) compounds have been obtained. Both compounds exhibit field-induced slow magnetic relaxation behaviour.

Slow magnetic relaxation in mononuclear octa-coordinate Fe(ii) and Co(ii) complexes from a Bpybox ligand

“…The τ 0 values of the two complexes are within the ordinary range of 10 −7 to 10 −10 s found in reported Fe( ii )- and Co( ii )-containing SIMs with high coordination numbers. 43–53…”

“…Using suitable ligands, some hepta- and octa-coordinated Fe( ii ) and Co( ii ) complexes were found to exhibit unique slow magnetic relaxation properties. 43–53 To date, all the reported examples have been constructed from O4, N4 or N2O2 ligands, indicating that the tetra-dentate ligands are prospective candidates towards octa-coordinate complexes. In particular, the neutral ligands impose a relatively weaker ligand field compared to the anionic ones.…”

Slow magnetic relaxation in Fe(ii)m-terphenyl complexes

“…This is likely due to rapid quantum tunnelling of magnetisation (QTM), which is commonly observed in mononuclear Fe( ii ) species. 20–24,26,27 However, 1–5 exhibit slow magnetic relaxation under an applied DC field. To determine the dependence of τ on field strength, AC susceptibility measurements were performed on 1–5 at 2 K (1–1400 Hz switching frequency) over a range of applied DC fields ( H = 100–5000 Oe).…”

“…13 The challenge for mononuclear 3d SMMs is that the crystal fields exerted on the metal centre by the ligands tend to quench the orbital angular momentum. This can be avoided through careful ligand design, and there have been a number of reports of Fe( i ), 14,15 Fe( ii ), 16–27 Co( ii ), 28–34 Ni( ii ), 35 and Mn( iii ) 36 complexes that display slow magnetic relaxation. Among these, two-coordinate metal centres in linear or near-linear geometries, most notably [Co{C(SiMe 2 O-1-naphthyl) 3 } 2 ], 34 have shown the best performance in terms of magnetic blocking temperature and open hysteresis 15,24,28,34 as their large magnetic anisotropy inhibits quenching of the orbital angular momentum.…”

Slow magnetic relaxation and spin crossover behavior in two mixed-valence Co(ii)/Co(iii) complexes

“…31–33 Searching for well-defined correlations between different structural factors and the magnetic anisotropy in transition metal complexes remains a great challenge and much more work is required to extend our knowledge for the rational design of new magnetic materials. 33–40…”