Low-temperature structural studies of molecularβ′−Pd(dmit)2conductors

X-ray diffraction investigation was performed at low temperatures in ${\beta }^{\prime }-\left({\mathrm{Et}}_2{\mathrm{Me}}_{2}Z\right)\left[\mathrm{Pd}\right(\mathrm{dmit}{)}_2{]}_2$ and ${\beta }^{\prime }-\left({\mathrm{Me}}_{4}Z\right)\left[\mathrm{Pd}\right(\mathrm{dmit}{)}_2{]}_2\hspace{0.5em}(Z=\mathrm{P},\mathrm{S}\mathrm{b})$ isostructural salts. We measured the thermal contraction of the crystal lattice and performed structural refinements and tight-binding band-structure calculations at room temperature and 8 K. Variations in the electronic band structures are discussed in relation with the structural changes and with the influence of the cation on the crystal structure. We point out the possibility of magnetic frustration within the molecules’ layers at low temperature when the anisotropy of the interactions between the dimers of $\mathrm{Pd}(\mathrm{dmit}{)}_2$ molecules is considered. We also report the existence of superlattice reflections in the ${\mathrm{Et}}_2{\mathrm{Me}}_{2}Z$ salts which correspond to an orientational cation ordering at low temperature.