Nonlinear Conductive Behavior of 2D-Selenido Stannates

Chalcogenido metalates have long been regarded as cluster-based semiconductors, yet their conductive nature has not been studied in detail, although such compounds do bear potential for use in electronics. Herein, we introduce four new compounds, (HDMMP)$_2$[Sn$_3$Se$_7$]·(HDMMP)$_2$[Sn$_2$Se$_6$]$_{0.5}$ (1), (C$_3$C$_1$Im)$_3$(HDMMP)[Sn$_3$Se$_7$]$_2$ (2), and their Cs$^+$-exchanged derivatives, 1$^{Cs}$ and 2$^{Cs}$ (HDMMP = protonated 2,6-dimethylmorpholine; C$_3$C$_1$Im = 1-propyl-3-methyl-imidazolium), all of which are based on 2D-{[Sn$_3$Se$_7$]$^{2–}$} anionic substructures. Detailed current–voltage measurements on single crystals of 1 and 2 as well as their ion-exchanged derivatives were undertaken that indicated complex nonlinear and highly structure-dependent conductive properties. For 1, the studies demonstrate that intercalation of molecular 0D-[Sn$_2$Se$_6$]$^{4–}$ units with higher negative charge density as compared to the 2D-{[Sn$_3$Se$_7$]$^{2–}$} networks creates open circuits that lead to nonconductive characteristics. In contrast, the I–V measurements carried out on 2 suggest a combination of electrical and ionic conductivity along horizontal and vertical directions of this compound based exclusively on the 2D-{[Sn$_3$Se$_7$]$^{2–}$} substructures. ... mehrCation exchange in 1 and 2 with Cs$^+$, which in the case of compound 1 is accompanied by an extraction of the molecular anions 0D-[Sn$_2$Se$_6$]$^{4–}$, confirms this suggestion: a set of I–V characteristics, including I–V hysteresis and chronoamperometry traces, demonstrate that both compounds are now conductive, with ionic conductivity dominating along both vertical and horizontal directions of 1$^{Cs}$ and 2$^{Cs}$. Notably, compound 1 not only turned into a conductive material 1$^{Cs}$, it additionally became slightly more conductive this way than 2$^{Cs}$. In summary, this work unravels the nonlinear conductive nature of selenido stannates and represents a step forward toward functional materials based on chalcogenido metalates.