Properties of N${\mathrm{H}}_4$${\mathrm{N}\mathrm{i}\left[{\mathrm{S}}_2{\mathrm{C}}_2\mathrm{}\right(\mathrm{CN}\left)\right]}_2$. ${\mathrm{H}}_2$O

Single crystals of N${\mathrm{H}}_4$ ${\mathrm{N}\mathrm{i}\left[{\mathrm{S}}_2{\mathrm{C}}_2{\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_2\right]}_2$. ${\mathrm{H}}_2$O have been grown. The single-crystal resistivity in the high-conductivity direction ($\rho \simeq 20$ Ω cm) is the lowest observed for salts formed with the anion ${\left\{{\mathrm{N}\mathrm{i}\left[{\mathrm{S}}_2{\mathrm{C}}_2{\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_2\right]}_2\right\}}^{-}$. A phase transition is observed in both resistivity and magnetic susceptibility in the temperature range 200 > T > 130 K. This transition is paralleled by several temperature-dependent absorptions in the infrared (IR). Resonance Raman spectroscopy suggests that these absorptions may be associated with $A_g$ modes which become infrared active via a vibronic interaction. These observations are consistent with a dimerization on the anion stack with decreasing temperature.