Determination of Large Zero-Field Splitting in High-Spin Co(I) Clathrochelates

Abstract

Zero-field splitting (ZFS) of three high-spin Co­(I) (S = 1) clathrochelate complexes was determined by frequency-domain Fourier-transform THz-EPR (FD-FT THz-EPR). The following axial and rhombic ZFS values (D and E, respectively) were determined: [N­(n-Bu)4]­CoI(GmCl2)3(BPh)2 (1, D/hc = +16.43(1) cm–1, E/hc = 0.0(1) cm–1), [P­(Me2N)4]­CoI(GmCl2)3(BPh)2 (2, D/hc = +16.67(4) cm–1, E/hc = 0.0(1) cm–1), and [P­(C6H5)4]­CoI(GmCl2)3(BPh)2 (3, D/hc = +16.72(2) cm–1, E/hc = 0.24(3) cm–1). Complementary susceptibility χT measurements and quantum chemistry calculations on 1 revealed hard-axis-type magnetic anisotropy and allowed for a correlation of ZFS and the electronic structure. Increased rhombicity of 3 as compared to 1 and 2 was assigned to symmetry changes of the ligand structure induced by the change of the counterion. 1 and 3 exhibited temperature-dependent ZFS values. Possible reasons for this phenomenon, such as structural changes and weak chain-like intermolecular antiferromagnetic interactions, are discussed.

Single‐Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain

“…This can be rationalized by the AF magnetic ordering of the chains, which means that additional energy is required for the excited spin to overcome the interchain interaction below the critical temperature T c .I narecent FD-FT THz-EPR study on mononuclearh igh-spin cobalt(I) clathrochelate complexes, a similar phenomenonw as observed in the form of an increase of the zero-field resonance energy with temperature. [19] It was interpreted in terms of weak AF interactions, however,b etween single molecules instead of 1D chains.…”

A Trigonal Prismatic Cobalt(II) Complex as a Single Molecule Magnet with a Reduced Contribution from Quantum Tunneling

“…At conventional frequencies, they are almost always EPR-silent, as the transition M S = À S↔ + S is forbidden by the selection rules for large S, and high-lying M S = � 1/2 Kramer's doublet is unpopulated. At extremely high frequencies, however, THz-EPR spectroscopy can access the inter-Kramer's transition M S = � S↔ � (SÀ 1) and therefore directly measure the ZFS value, [23][24][25][26][27][28] which is the key characteristic of an SMM related to the energy U of the magnetization reversal barrier U = 2|D| with D being a zero-field splitting energy.…”

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

“…Better estimates of ZFS parameters were obtained from field‐dependent FD‐FT THz‐EPR, which allows for an accurate determination of large ZFS even in integer spin ‘EPR silent’ transition metal ions. [ 68 , 69 , 70 ] The instrument at BESSY II[ 61 , 62 ] detects EPR in the frequency domain via FTIR transmission spectroscopy on samples that can be exposed to strong external magnetic fields and cryogenic temperatures; technical details are included in the Supplementary Information. Simulations were performed in EasySpin,[ 71 , 72 ] assuming a pure S =1 spin Hamiltonian: …”