Structural and Magnetic Investigations on the CT Ion-Radical Salt (p-(Dimethylamino)phenyl)dimethylammonium Bis(maleonitriledithiolato)nickelate(III)

A detailed study of (TMPD)Ni(mnt)₂ by a variety of physical methods X-ray crystallography, electronic absorption spectroscopy, magnetic susceptibility, electrical conductivity, and EPR has been carried out. Though Ni(mnt)₂- and TMPD⁺ form segregated stacks along the “a” axis in the triclinic modification P1, a number of short contacts between the units facilitate charge transfer from TMPD⁺ to Ni(mnt)₂”. Both susceptibility and EPR studies indicate two temperature regions, T < 100 K and T > 100 K. In the T < 100 K region, where the behavior is Curie-Weiss type, the decomposition of total susceptibility shows that at 4.2 K about 90% of the contribution comes from the Ni(mnt)₂- stack. A value of exchange (~ 120 cm^″1) has been found from the dependence of χ on temperature in the T > 100 K region. Powder EPR studies yielded a ratio of D_c J to be 1.94 × 10^″2. Single-crystal EPR studies at 77 K clearly indicate a change in the principal axis cosines and from line width analysis in the plane perpendicular to “a” give the best fit for J = -6.5 cm^-1, De = -0.13 cm^″1, and p = 5. The line shape analysis shows low-dimensional behavior for B\\a and nearly Lorentzian behavior for Ba.