Magnetostructural relations from a combined ab initio and ligand field analysis for the nonintuitive zero-field splitting in Mn(III) complexes

Abstract

The zero-field splitting (ZFS) of a model monometallic Mn(III) complex is theoretically studied as function of a systematic symmetry lowering. First, we treat the octahedral case for which the standard S.D.S model Hamiltonian cannot be applied due to a zero-field splitting in the absence of anisotropy induced by the spin-orbit coupling between the two spatial components of the (5)E(g) state at second-order of perturbation. Next, the symmetry is lowered to D(4h) and D(2h) and the anisotropic spin Hamiltonian is extracted using effective Hamiltonian theory. A simple relation is derived between the ratio E//D/ and the applied rhombic and axial distortions. Moreover, it is shown that close to O(h) symmetry, the orbital mixing due to spin-orbit coupling can be accurately described with Stevens fourth-order operators. The calculated tendencies are interpreted within a refined Racah plus ligand field model and it is shown that the ZFS parameters in Mn(III) complexes follow special rules that are nonintuitive compared to other d(n) configurations. Finally, some angular distortions are applied to study their effect on the anisotropy.

Zero-field splitting in nickel(II) complexes: A comparison of DFT and multi-configurational wavefunction calculations

“…Similar conclusions for other Mn(III) systems were reached in other papers from Neese's group. 26,79,80 Moreover, some model Mn(III) complexes were the topic of an ab initio study by Maurice et al 81,82 The conclusion of this discussion might be that the difficult systems, with spatially nearly degenerate states, require the use of the most advanced theoretical tools, such as the NEVPT2/QDPT combination. What is surprising, to a certain extent, is the fact that our calculations for the apparently "easy" case of nickel(II), with the triplet ground state quite far below the excited states, show the same trend as the "difficult" ions.…”

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

“…Nevertheless, if we consider a special category of SMMs with one paramagnetic center, so called single-ion magnets (SIMs), then the deliberate modulation of the magnetic anisotropy is easier and depends reasonably on the topology and donor atom constitution of the coordination polyhedron [2]. Up to now, several correlations on the relationship between a structure and anisotropy parameters have been reported, namely for tetracoordinate [8,9], pentacoordinate [10,11], hexacoordinate Ni II and Co II compounds [12,13], tetracoordinate Fe II compounds [14] and penta and hexacoordinate Mn III compounds [15,16]. From these, the largest number of complexes exhibiting slow-relaxation of magnetization belongs undoubtedly to the group of tetracoordinate Co II compounds, which we have chosen as an object of the present study.…”

Effect of Second‐Order Spin–Orbit Coupling on the Interaction between Spin States in Spin‐Crossover Systems

“…[13] This transformation from the real space to the time domain implies great computational savings andh as been successfully applied to determinei ntersystem crossing rates in moleculesr elevant to singlet fission, [14] photorelaxation of nucleobases, [15] spin crossoveri nF e II and Fe III complexes, [16,17] and the photophysicso fi ridium-based organic light-emitting diods (OLEDs), [18] among other applications. (2)]: [26][27][28] There is av ast literature on how to efficientlyc alculate accurate relative electronic energies.…”

“…This involves the indirect interaction between the states mediated by other (excited) electronic states as reflected in the second term of the expression derived from the quasi degenerate perturbation theory (QDPT) of the spin–orbit coupling between the states i and j [Eq. ]: …”