Temperature-dependent crystal structures and unusual dielectric property in [Me2NH2]2[Ni(mnt)2]

• The novel salt, [(CH3)2NH2]2[Ni(mnt)2], shows a 0 dimensional cation–anion structure.
• The variation of hydrogen bonds affects the temperature-dependent structure of the complex.
• The structural changes are reflected in the reversible dielectric transition.

The title compound bis(dimethylammonium) bis(dicyanoethene-1,2-dithiolato)-nickel (II) undergoes a reversible dielectric transition occurring at about 260 K. The variable-temperature X-ray structural determinations reveal that both phases are monoclinic, space group C2/c with a = 16.383(3), b = 9.521(5), c = 13.631(3) Å, β = 118.28(3)°, V = 1872.5(8) Å3 at the room temperature (293 K), and with a = 15.885(5), b = 9.418(0), c = 13.771(3) Å, β = 116.89(3)°, V = 1837.4(8) Å3 at the low temperature (93 K). The [Ni(mnt)2]2 − anions form a non-uniform stacking pattern and interact with the [Me2NH2]+ cations by N–H∙∙∙S, N–H∙∙∙N hydrogen bonds, for the two phases. With temperature increasing, the cations and anions are shifting and thus result in the significant changes of the hydrogen bonds. The effect of these shifts is reflected in the dielectric behavior of the [Me2NH2]2[Ni(mnt)2] salt (mnt2 − = maleonitriledithiolate).

The novel complex bis(dimethylammonium) bis(dicyanoethene-1,2-dithiolato)-nickel (II), [Me2NH2]2[Ni(mnt)2], has been synthesized and investigated its temperature-dependent crystal structures and dielectric property. With temperature increasing from 93 K to 293 K, both the cations and anions are shifting in the stack and result in the significant changes of the hydrogen bonds, however, with no change in the space group. These structural changes are reflected in the reversible dielectric transition.Figure optionsDownload as PowerPoint slide