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

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 (ClO₄ )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 (NO₃ )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.

Effect of Co(2+) and Ni(2+)-doped zinc borate nano crystalline powders by co-precipitation method

A simple co-precipitation method has been used for the synthesis of Co(2+) and Ni(2+)-doped zinc borate nanopowders. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV/Vis absorption, Scanning electron microscope (SEM) with EDS and photoluminescence (PL) spectroscopies techniques has been employed for their characterization. Powder X-ray diffraction data reveals that the crystal structure belongs to monoclinic for both as-prepared samples. SEM images showed surface morphology of the prepared samples. Optical absorption spectra showed the characteristic bands of doped ions in octahedral site symmetry. From the optical absorption data crystal field and inter-electronic repulsion parameters are evaluated. The FT-IR spectra showed the characteristic vibrational bands related to ZnO, BO3 and BO4 molecules. Photoluminescence spectra exhibited the emission bands in ultraviolet and blue regions.

EPR and optical studies of Nickel(II) at 300 K

Single crystal EPR studies of Ni(II) in hexaimidazolecobalt(II) dichloride tetrahydrate have been carried out at ambient temperature to obtain g and zero-field tensors, making it one of the very few systems having room temperature EPR data. The results show rhombic distortion around the Ni(II) ion, with the ion being entered the lattice substitutionally in place of Co(II). The optical data suggest trigonally distorted electronic structure around Ni(II) and collaboration with EPR data provided a few bonding parameters.