Field-induced slow magnetic relaxation in pseudooctahedral cobalt(ii) complexes with positive axial and large rhombic anisotropy

Abstract

The preparation, X-ray crystal structure, spectroscopic and variable-temperature dc and ac magnetic properties of two six-coordinate cobalt(ii) complexes of formula [Co(bim)4(tcm)2] (1) and [Co(bmim)4(tcm)2] (2) are reported.

Single‐Ion Magnetic Behaviour in an Iron(III) Porphyrin Complex: A Dichotomy Between High Spin and 5/2–3/2 Spin Admixture

“…Owing to the small change in χ M T at high temperature (300–40 K) pointing to a modest extent of spin admixture, the lowest‐lying Kramers doublets can be described by a ZFS model for S= 5/2. Although analysis of the χ M T versus T plot at higher temperatures with the ZFS model is limited, adding a temperature‐independent paramagnetism (TIP) that accounts for a depopulation of the first quartet excited state with decreasing temperature is a useful alternative to the spin‐admixed model [42–44] . Such depopulation on cooling can lead to an increase of the χ M T product and a negative value of the TIP.…”

Single molecule magnets of cobalt and zinc homo- and heterometallic coordination polymers prepared by a one-step synthetic procedure

“…[73][74][75][76] The observed behavior and anisotropic values are similar to other published mononuclear Co(II) complexes in pseudo-octahedral geometry and also in other Co(II) CPs. [77][78][79][80][81][82] Dynamic susceptibility measurements were performed to study the possibility of slow relaxation of the magnetization. Without an applied static dc eld, no c 0 signal was observed; however, when an external dc eld was used, a dependence of c 0 appeared.…”

Trigonally Distorted Hexacoordinate Co(II) Single-Ion Magnets

“…Hexacoordinate Co(II) complexes often tend to possess very large magnetic anisotropies arising from the direct contribution of spin orbit coupling to the ground state. If the coordination geometry is regular octahedron, the ground state is 4 T 1g . Then, angular momentum is the main contributor to the zero-field splitting (ZFS), because the spinorbit coupling operator transforms under t 1g , thus it directly mixes with the ground state.…”

“…The design of highly anisotropic magnetic molecules exploits changing of the regular octahedral geometry, which can be achieved either by elongation/compression of the metal-ligand bonds or by trigonal distortion. Both types of distortion can lead to double orbitally degenerate ground states ( 4 E g for compressed octahedron, D 4h , 4 E for trigonal prism, D 3h ), manifesting themselves again by a large contribution of spin-orbit coupling to the ground state. However, contrary to the 4 T 1g state [3,4], the anisotropy of E-states is of the axial character [5].…”

“…Both types of distortion can lead to double orbitally degenerate ground states ( 4 E g for compressed octahedron, D 4h , 4 E for trigonal prism, D 3h ), manifesting themselves again by a large contribution of spin-orbit coupling to the ground state. However, contrary to the 4 T 1g state [3,4], the anisotropy of E-states is of the axial character [5]. Thus, Co(II) complexes with doubly degenerate ground states are highly interesting for synthesis of single-ion magnets (SIMs), which are a class of singe molecule magnets (SMMs) [6] containing only one paramagnetic center [7].…”