Interpretation of EPR and optical spectra of Ni(II) ions in crystalline lattices at ambient temperature

Abstract

Many biologically important paramagnetic metal ions are characterized by electron paramagnetic resonance (EPR) spectroscopy to use as spin probes to investigate the structure and function of biomolecules. Though nickel(II) ions are an essential trace element and part of many biomolecules, the EPR properties are least understood. Herein, the EPR and optical absorption spectra measured at 300 K for Ni(II) ions diluted in two different diamagnetic hosts are investigated and reported. The EPR spectrum of a polycrystalline Ni/Mg (3-methylpyrazole) 6 (ClO 4 ) 2 [Ni/MMPC] shows two transitions at X-band frequency ($9.5 GHz), suggesting the zero-field splitting parameter (D) is larger than the resonance field of the free electron (H o ). This incomplete and complex spectrum is successfully analyzed to obtain EPR parameters. The EPR spectrum of the polycrystalline Ni/Zn(pyrazole) 6 (NO 3 ) 2 [Ni/ZPN] shows a triplet spectrum indicating D < H o . A detailed analysis of single-crystal EPR data yielded the spin Hamiltonian parameters. The optical absorption spectra are deconvoluted to understand the symmetry of the coordination environment in the complex.

Efficient NH3-Tolerant Nickel-Based Hydrogen Oxidation Catalyst for Anion Exchange Membrane Fuel Cells

“…Using the method described by Pearson and co-workers, we determined the occupancies of the 3d electron to be 6.4 for MoNi 4 and 7.5 for Cr-MoNi 4 (inset in Figure d). The increase in the d-band filling of Cr-MoNi 4 over MoNi 4 suggests its electron-rich surface that can restrain the σ N–H → d donation. − Furthermore, electron paramagnetic resonance (EPR) measurements yield signals at a g -factor of 2.1446 for MoNi 4 and 2.1679 for Cr-MoNi 4 (Figure e), both corresponding with metallic Ni. − The slight difference of the g -factor could be the result of Cr incorporation . We compared the double integration intensity of the EPR signals to offer spin density information on the catalysts.…”

Unveiling the atomistic and electronic structure of NiII–NO adduct in a MOF-based catalyst by EPR spectroscopy and quantum chemical modelling

“…Only a very few Ni II -containing materials were characterized employing X-and Q-band EPR spectroscopy for Ni II species having smaller or comparable ZFS to the MW frequency. [64][65][66] In order to overcome these complications, CW high-frequency EPR (HFEPR) spectroscopy techniques, [67][68][69] (B90 GHz to B611 GHz and magnetic fields up to B22 T) and even timedomain terahertz EPR measurements 70 were utilized to acquire the complete triplet spectrum of the S = 1 Ni II species. Furthermore, temperature-and field-dependent magnetic susceptibility measurements also provided spin Hamiltonian parameters for such high-spin Ni II systems.…”

Ligand field design enables quantum manipulation of spins in Ni2+ complexes

“…In the orbitally non-degenerate case, this can be achieved via incorporation of strong eld ligands, as D is inversely proportional to the energetic separation of excited states from the ground state. 25 Previously, the only examples of commercial frequency [26][27][28][29][30][31][32][33] which are exceptionally host-and counterion-dependent, due to the weak eld monodentate ligands and the exible primary coordination sphere. As a result, for a nickel coordination complex with the same coordinating ligands, D can vary by an order of magnitude as a function of counterion.…”