a FD-FT THz-EPR study

A combined X-band and frequency-domain Fourier-transform THz electron paramagnetic resonance (FD-FT THz-EPR) approach has been employed to determine heme Fe(III) S = 5/2 zero-field splitting (ZFS) parameters of frozen metHb and metMb solutions, both with fluoro and aquo ligands. Frequency-domain EPR measurements have been carried out by an improved synchrotron-based FD-FT THz- EPR spectrometer. ZFS has been determined by field dependence of spin transitions within the mS = ±1/2 manifold, for all four protein systems, and by zero-field spin transitions between mS = ±1/2 and mS = ±3/2 levels, for metHb and metMb flouro-states. FD-FT THz-EPR data were simulated with a novel numerical routine based on Easyspin, which allows now for direct comparison of EPR spectra in field and frequency domain. We found purely axial ZFSs of D = 5.0(1) cm−1 (flouro-metMb), D = 9.2(4) cm−1 (aquo-metMb), D = 5.1(1) cm−1 (flouro-metHB) and D = 10.4(2) cm−1 (aquo-metHb)

Coordination [CoII2] and [CoIIZnII] helicates showing slow magnetic relaxation

The slow magnetic relaxation of CoII ions in the elusive intermediate geometry between the trigonal prism and antiprism has been studied on the new [Co2L3]4+ and [CoZnL3]4+ coordination helicates [L is a bis(pyrazolylpyridine) ligand]. Solution paramagnetic 1H NMR and solid-state magnetization measurements unveil single-molecule-magnet behavior with small axial anisotropy, as predicted previously

Easy-plane to easy-axis anisotropy switching in a Co(ii) single-ion magnet triggered by the diamagnetic lattice

Single ion magnets SIMs with large magnetic anisotropy are promising candidates for realization of single molecule based magnetic memory and qubits. Creation of materials with magnetically uncoupled spatially separated SIMs requires dilution in a diamagnetic matrix. Herein, we report that progressive dilution of paramagnetic Co II by diamagnetic Zn II in the SIM [CoxZn 1 amp; 8722;x piv 2 2 NH2 Py 2], x 1 0 beyond a threshold of 50 reveals an abrupt structural change, where the distorted tetrahedral Zn coordination structure is superimposed on the remaining Co ions, which were initially in a distorted octahedral environment. Dilution induced structure modification switches the magnetic anisotropy from easy plane D 36.7 cm amp; 8722;1 to easy axis type D amp; 8722;23.9 cm amp; 8722;1 , accompanied by a fivefold increase of the magnetic relaxation time at 2 K. Changes of the static and dynamic magnetic properties are monitored by electron paramagnetic resonance spectroscopy and AC susceptibility measurements. Complementary quantum chemical ab initio calculations quantify the influence of structural changes on the electronic structure and the magnetic anisotropy. Thus, magnetic dilution hits two goals at once, the creation of isolated magnetic centres and an improvement of their SIM propertie