Three tetracoordinate Co(ii) complexes [Co(biq)X₂] (X = Cl, Br, I) with easy-plane magnetic anisotropy as field-induced single-molecule magnets

Abstract

Three mononuclear complexes [Co(biq)X2] (biq = 2,2'-biquinoline; X = Cl, Br, I) were prepared by a solvothermal method and characterized by single-crystal X-ray diffraction. In all three complexes the Co(ii) atom is tetrahedrally coordinated by one biq ligand bonded in a chelate manner and two halogenido ligands. Hydrogen bonding interactions (C-HX) along with the π-π interactions contribute to the stability of the formed packing. Magnetic measurements as well as ab initio calculations revealed that the complexes possess a sizable easy-plane magnetic anisotropy (D > 0). They display a superparamagnetic behaviour in an applied external field that culminates between BDC = 0.2-0.3 T. Two relaxation processes are observed; the faster can be analysed in terms of the direct and Orbach processes yielding U/kB = 42.6 K and τ0 = 1.9 × 10(-10) s for X = Cl, U/kB = 39.6 K and τ0 = 1.2 × 10(-10) s for X = Br and U/kB = 57.0 K and τ0 = 3.2 × 10(-13) s for X = I at BDC = 0.2 T.

Field‐Induced Slow Magnetic Relaxation of GdIII Complex with a Pt−Gd Heterometallic Bond

“…Recently,t here have been af ew reports on field-induced slow magnetic relaxation, which is caused by aK ramers doublet brought about by nuclear spin [5] or the low symmetry of the metal ion. [19] These complexes and the Gd complexes reportedh ere have similar magnetic properties, such as field-induced frequency dependent c"a nd butterfly-type hysteresis, which is observed in magnetizationv ersus field plots. [19] In these cases, the m j states are very close to each other or mixed.H ence, QTM was dominant, and c"w as not frequency dependentw ithoutadc field.…”

“…[19] These complexes and the Gd complexes reportedh ere have similar magnetic properties, such as field-induced frequency dependent c"a nd butterfly-type hysteresis, which is observed in magnetizationv ersus field plots. [19] In these cases, the m j states are very close to each other or mixed.H ence, QTM was dominant, and c"w as not frequency dependentw ithoutadc field. In such complexes, in which transversal interstate transitions block magnetization, direct and Raman process are dominant.…”

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

“…Thus, we performed a search in the CSD database (version 5.37 updated to May 2016) [22] for interesting candidates within the group of [Co(L N ) 2 (Cl) 2 ] compounds, which are readily synthetically available. Furthermore, in the previous works [9,17,23,24,25] the influence of the change in the α angle on D was well documented and therefore, we decided to study a compound with a large β angle, which should also lead to negative δ and D . From the CSD search we know that the average and median β values are both larger (114.1° and 114.4°) than the ideal tetrahedral angle.…”

Field‐Supported Single‐Molecule Magnets of Type [Co(bzimpy)X2]

“…Some systems exhibit a single relaxation path, whereas some show two or three relaxation channels, usually supported by an external magnetic field. [5c], [5f], [6d], [8b], …”