Electronic Structure of [NiS4]-Investigated by Single-Crystal EPR and Density Functional Theory

Abstract

To understand the electronic structure of <TEX>$[NiS_4]^-$</TEX> complex ions, two complexes with such <TEX>$[NiS_4]^-$</TEX> core, <TEX>$FcCH=CHPymCH_3[Ni(dmit)_2]$</TEX> (Pym = pyridinium, <TEX>$dmit^{2-}$</TEX> = 2-thioxo-1,3-dithiole-4,5-dithiolate) and <TEX>$FcCH=CHPymCH_3[Ni(dddt)_2]{\cdot}{\frac{1}{2}}H_2O$</TEX> (<TEX>$dddt^{2-}=5,6-dihydro-1,4-dithiin-2,3-dithiolato$</TEX>), were synthesized to be characterized by X-ray crystallography, single crystal electron paramagnetic resonance (EPR) and density functional theory (DFT) calculation. Powder EPR spectra show narrow g-anisotropy but the anisotropy is bigger in <TEX>$[Ni(dmit)_2]^-$</TEX> than in <TEX>$[Ni(dddt)_2]^-$</TEX>, indicating bigger spin density in Ni(III) d-orbital of <TEX>$[Ni(dmit)_2]^-$</TEX> than in <TEX>$[Ni(dddt)_2]^-$</TEX>, which is consistent to DFT results. EPR studies of the crystals of the complexes surprisingly suggest that the <TEX>$g_y$</TEX>-axis of <TEX>$[Ni(dddt)_2]^-$</TEX> is approximately on or perpendicular to the <TEX>$[NiS_4]^-$</TEX> plane while the <TEX>$g_y$</TEX>-axis of <TEX>$[Ni(dmit)_2]^-$</TEX> is on the plane, though DFT study of the complexes of this study and previously reported <TEX>$[NiS_4]^-$</TEX> complexes indicate that the <TEX>$g_y$</TEX>-axis is on the <TEX>$[NiS_4]^-$</TEX> plane.