Single-ion magnet behaviour in homoleptic Co(ii) complexes bearing 2-iminopyrrolyl ligands

Abstract

Four-coordinate distorted tetrahedral bis(2-iminopyrrolyl)cobalt(ii) complexes behave as Single-Ion Magnets (SIMs) in the absence of an external magnetic field.

Enhancing SIM behaviour in a mononuclear tetrahedral [Co(N,N′-2-iminopyrrolyl)2] complex

“…The elongated tetrahedral geometry in this compound (ligand bite angles y of 84.38(15) and 84.43(15)1), the large value of the angle f and the relatively low value of angle o contribute all together to the observed negative value of D (À42.6(4) cm À1 ), in agreement with the magnetostructural analysis previously carried out. 10 Additionally, the QTM process at zero field exhibits a residual value in complex 1, as confirmed by the similar behaviour observed with and without an applied magnetic field, and in agreement with the theoretical calculations. This is attributed to a lower value of the zero-field splitting parameter E (0.4(2) cm À1 ).…”

“…Up to now, there have been few tetrahedral Co(II) complexes displaying SIM behaviour in the absence of an external magnetic field. [3][4][5][6][7][8][9][10] With ligand fields of the highest symmetry (T d ) their second-order zero-field splitting (ZFS) should be strictly zero even if there is significant spin-orbit coupling (SOC), but under lower symmetries, e.g. using bidentate ligands, these complexes may acquire significant ZFS.…”

“…9 Recently, we reported a comprehensive study of a series of four homoleptic mononuclear neutral bis(2-iminopyrrolyl) Co(II) complexes, comprising structural, magnetic, spectroscopic and theoretical studies, proving their SIM behaviour. 10 All the compounds presented elongated tetrahedral geometries, which were responsible for the large and negative values of D. The study of their molecular structures by X-ray diffraction revealed that the increase of the ligand bulkiness leads to a geometry closer to tetrahedral (confirmed by the corresponding t 4 11 parameters and the chelating ligands interplanar angles f), resulting in the appearance of frequency-dependent maxima in both the in-phase and out-of-phase components of the AC magnetic susceptibility (w 0 and w 0 , respectively) vs. T plots, without the application of a DC field. In view of these observations, we were still challenged by the steric limits of the 2iminopyrrolyl framework.…”

“…In view of these observations, we were still challenged by the steric limits of the 2iminopyrrolyl framework. Thus, we considered whether it would be synthetically possible to employ a chelating ligand of this family bulkier than that of the highly hindered and previously synthesised 1-adamantyl derivative, 10 Magnetic studies were also carried out, namely room temperature magnetic susceptibility measurements in solid state using both static (DC) and dynamic (AC) measurements.…”

“…By keeping the energy barrier fixed to U eff = 85 cm À1 (corresponding to (S 2 À 1/4)|D| = 2|D|, for S = 3/2 using the experimental value of D = À42.6(4) cm À1 ), the remaining parameters were obtained as C = 0.040(9) K Àn s À1 , n = 5.1(1) and t 0 = 2.1(1) Â 10 À9 s, where n is within the values calculated for other Co(II) complexes reported in the literature. 8,10,17 Up to a field H DC of 1200 Oe no changes in the magnetic relaxation parameters were observed since, by overlaying the ln(t) vs. T À1 plots, both curves remain almost superimposable (Fig. S11, ESI †).…”