Large easy-axis magnetic anisotropy in a series of trigonal prismatic mononuclear cobalt(ii) complexes with zero-field hidden single-molecule magnet behaviour: the important role of the distortion of the coordination sphere and intermolecular interactions in the slow relaxation

Abstract

The complexes [Co(L)]X·S (X = CoCl42- , S = CH3CN (1); X = ZnCl42- , S = CH3OH (2)), [Co(L)]X2·S (X = ClO4-, S = 2CH3OH (3) and X =...

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

“…By keeping the energy barrier fixed to U eff = 85 cm −1 (corresponding to ( S 2 − 1/4)| D | = 2| D |, for S = 3/2 using the experimental value of D = −42.6(4) cm −1 ), the remaining parameters were obtained as C = 0.040(9) K − n s −1 , n = 5.1(1) and τ 0 = 2.1(1) × 10 −9 s, where n is within the values calculated for other Co( ii ) complexes reported in the literature. 8,10,17…”

Impact of Spin-Phonon Coupling on Magnetic Relaxation of a Co(II) Single-Molecule Magnet

“…Out of curiosity, we included the extended double d-shell in the active space CAS(7,10) and found a consistent positive sign of D both in CASSCF and NEVPT2 calculations (Table S4 in SI). To come to an end, it has been deduced that the dynamical correlations play major role in determining the accurate sign of D. Additionally, the extended double d-shell in active space may also be advantageous to have consistent sign of D. This kind of ambiguity has been reported by Singh et al 54 earlier and by Gereka et al 31 only recently suggesting the requirement of specific theoretical calculations or the experimental techniques like HFEPR to determine the magnetic anisotropy for this kind of complex reliably. The lowest spin-free energies for all the complexes along with the corresponding contribution to D and E values are enlisted in Table 3.…”

“…Besides, this Co(II) system owing to Kramers ground state, is presumed not to relax largely via direct and under-the-barrier QTM process, in the vicinity of zero external magnetic field. 31 Consequently, it is deduced to have slow magnetic relaxation, likely in absence of any field, and is anticipated to demonstrate magnetic hysteresis. The number at each arrow corresponds to mean absolute value of the corresponding matrix element of the transition magnetic moment.…”

“…[28][29][30] Into the bargain, Gereka and co-workers have explained the impact of the distortion of the coordination sphere on the slow relaxation for Co II N 6 trigonal prismatic cationic complexes. 31 Hitherto there are many reports available in the published literature regarding poly-coordinated Co(II) complexes yet theoretical work focused on an in-depth study on low-coordinated Co(II) complexes is limited. Besides, the low-coordinate metal complexes are more efficacious towards SMMs due to their controllable symmetry around the metal ions, which eventually leads to larger barrier heights for magnetization reversal.…”

Advanced Spectroscopic and Computational Studies of a Cobalt(II) Coordination Polymer with Single-Ion-Magnet Properties

“…Far-IR magneto-spectroscopy (FIRMS) ,− and frequency-domain Fourier transform terahertz EPR are two other direct methods to determine magnetic excited states, including a recent work by Lu, Nelson, and co-workers using terahertz time-domain EPR through a simple tabletop approach to probe the transitions between the spin levels in transition-metal complexes . Brackett and Richards have shown that electronic spin transitions (Δ m S = 0, ±1) between the ground and the excited KDs (Figure ) are magnetic-dipole-allowed by symmetry and selection rules in far-IR spectroscopy. , FIRMS has been used to study transitions between the two KDs, ,,− ,− giving, e.g., the energy gap 2 D ′ = 2­( D 2 + 3 E 2 ) 1/2 in S = 3/2 complexes. For high-spin Co II complexes with large ZFS (>30 cm –1 ), HFEPR operating in the sub-THz frequency range gives E / D ratio and g values. ,,,,− The combined use of FIRMS, EPR, and inelastic neutron scattering (INS) has been adopted recently to give ZFS parameters for such complexes. ,,,,− This approach is still at its early stage, requiring additional studies to understand its scope and applicability.…”