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[Sn₃Se₇]·(HDMMP)₂[Sn₂Se₆]0.5 (1), (C₃C₁Im)₃(HDMMP)[Sn₃Se₇]₂ (2), and their Cs⁺-exchanged derivatives, 1Cs and 2Cs (HDMMP = protonated 2,6-dimethylmorpholine; C₃C₁Im = 1-propyl-3-methyl-imidazolium), all of which are based on 2D-{[Sn₃Se₇]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-[Sn₂Se₆]4– units with higher negative charge density as compared to the 2D-{[Sn₃Se₇]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-{[Sn₃Se₇]2–} substructures. Cation exchange in 1 and 2 with Cs⁺, which in the case of compound 1 is accompanied by an extraction of the molecular anions 0D-[Sn₂Se₆]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 1Cs and 2Cs. Notably, compound 1 not only turned into a conductive material 1Cs, it additionally became slightly more conductive this way than 2Cs. In summary, this work unravels the nonlinear conductive nature of selenido stannates and represents a step forward toward functional materials based on chalcogenido metalates.