The translational diffusion constants, D-T, of the bis(maleonitriledithiolato)nickel anion and dianion, Ni(mnt)(2)(-) and Ni(mnt)(2)(2-), respectively, have been measured in acetone and ethyl alcohol solutions drawn through a microcapillary by reduced pressure at 25 degrees C. The translational radius, r(t), obtained from D-T is larger for Ni(mnt)(2)(2-) than for Ni(mnt)(2)(-) in both solvents. The larger r(t) for Ni(mnt)(2)(2-) is attributed to ion pairing with (n-Bu)(4)(N+), while Ni(mnt)(2)(-) does not appear to be ion paired. r(t) for Ni(mnt)(2)(-) has been used to determine the rotational radius, r(o), of this paramagnetic ion; r(o) has been used with ESR results to determine kappa(perpendicular to), the solvent interaction parameter for Ni(mnt)(2)(-) in several solvents. ESR studies of Ni(mnt)(2)(-) in dimethyl phthalate. (DMPT) and tris(2-ethylhexyl) phosphate (TEHP) have also been made. The analysis of the widths shows the reorientation of Ni(mnt)(2)(-) is fastest about its long in-plane axis by a factor of approximate to 3 in both solvents. The temperature dependence of the widths is discussed using the modified Stokes-Einstein-Debye (SED) model and the Vogel-Tammann-Fulcher (VTF) equation. The SED results indicate that Ni(mnt)(2)(-) has relatively weak interactions with both DMPT and TEHP. The ESR VTF parameters are consistent with those from viscosities and produce calculated values of the glass transition temperatures, T-g that are also in general agreement with experiment.