Tuning the magnetic ground state of a tetranuclear nickel(II) molecular complex by high magnetic fields

Abstract

Electron spin resonance and magnetization data in magnetic fields up to 55 T of a novel multicenter paramagnetic molecular complex [L2Ni4(N3)(O2C Ada)4](Cl O4) are reported. In this compound, four Ni centers each having a spin S = 1 are coupled in a single molecule via bridging ligands (including a µ4-azide) which provide paths for magnetic exchange. Analysis of the frequency and temperature dependence of the ESR signals yields the relevant parameters of the spin Hamiltonian, in particular the single ion anisotropy gap and the g factor, which enables the calculation of the complex energy spectrum of the spin states in a magnetic field. The experimental results give compelling evidence for tuning the ground state of the molecule by magnetic field from a nonmagnetic state at small fields to a magnetic one in strong fields owing to the spin level crossing at a field of ∼ 25 T.

High-Frequency EPR Instrumentation

“…BWOs are used by several groups mainly focused on the study of molecular magnetism [46][47][48][49]. These oscillators combine a relatively high power with excellent frequency tuning possibilities.…”

“…The MVNA developed by the company ABmm has an unrivaled dynamic range and has been used in several laboratories involved in multi-high-frequency EPR [45,49,57,73]. The sources up to 300 GHz are based on YIG oscillators in combination with harmonic generators.…”

“…Brunel et al [43][44][45] realized a multifrequency HF-EPR spectrometer, which is optimized for the study of high-spin systems and radical species. Several laboratories followed similar schemes and developed multi-high-frequency instruments dedicated to a particular class of samples [46][47][48][49]. These setups do not need to be particularly sensitive and are less suited for work on diluted species and double resonance experiments.…”

Interplay of Magnetic Exchange Interactions and NiSNi Bond Angles in Polynuclear Nickel(II) Complexes

“…HF-ESR in static magnetic fields was studied with a Millimeterwave Vector Network Analyzer (AB Millimetré) used for generation of millimeter-and submillimeter microwaves and phase locked detection of a signal. [35] The measurements have been performed in the frequency range from 80 GHz up to 350 GHz and in magnetic fields up to 15 T. The analysis and the simulation of the ESR spectra were done by means of the EasySpin toolbox for Matlab. [58] The analysis and the simulation of the temperature dependence of the magnetic susceptibility (T) were done by means of the julX simulation program.…”

“…These methods have already been proven as powerful tools for the investigation of magnetic interactions and spin states of molecular Ni(II) complexes. [35][36][37] …”