Revisiting cobaloxime(II) chemistry and clearing misconceptions of cobaloxime(II) in diamagnetic Ni(II) and Pd(II)...

Co(II) was doped into the diamagnetic one-dimensional framework of bis(dimethylglyoximato) Ni(II) and Pd(II) complexes [Ni/Pd^II(Hdmg)₂] (Hdmg = dimethylglyoximate anion) (hereafter referred to as Co@Ni and Co@Pd samples) to study magnetic properties as a potential spin qubit. In a previous report of electron paramagnetic resonance (EPR) spectroscopy of this compound prepared using the same doping strategy in the Ni matrix, a spectrum assigned to S = 1/2 Co(II) with g = 2.58, g = 2.26 g = 1.98 was observed. The relatively large g value, compared to those typically observed in [Co(Hdmg)₂B] complexes (B = Lewis base ligand, x = 1 or 2), which fall within the ranges g = 2.1-2.4, g = 2.0-2.2 and g ≈ 2.01, led to the interpretation of this species to be Co(Hdmg)₂ with an extremely axial interaction. However, our EPR analysis, combined with SQUID (superconducting quantum interference device) and XANES (X-ray absorption near-edge structure) analyses, revealed that the previously identified species are μ-O bridged dimers: [Co(Hdmg)(μ-Hdmg)]₂ and [Co(Hdmg)(μ-Hdmg)][Ni/Pd(Hdmg)(μ-Hdmg)]. Furthermore, our liquid-helium temperature EPR spectra revealed a Co species with much greater axial g anisotropy (g = 4.75 g ≈ 0.75 for Co@Ni and g = 4.2 g ≈ 1.33 for Co@Pd). We assign this species to the truly planar Co(Hdmg)₂ with negligibly weak axial interaction, which might have been overlooked in previous EPR studies.