Varied forms of lamellar [Sn3Se7]n2n− anion: the competitive and synergistic structure-directing effects of metal–amine complex and imidazolium cations

Abstract

Presented are the syntheses, characterizations and properties of a series of selenidostannate compounds directed by metal–amine complex (MAC) cations and/or [Bmmim]⁺ (Bmmim = 1-butyl-2,3-dimethylimidazolium). Mixtures of the ionic liquid (IL) (Bmmim)Cl and amines, such as ethylenediamine (en) and diethylenetriamine (dien), in various ratios were used to ionothermally/solvothermally prepare four selenidostannates, namely, [Mn(en)₃]Sn₃Se₇ (1), [Mn(dien)₂]Sn₃Se₇·H₂O (2), (Bmmim)₃[Mn(en)₃]₂[Sn₉Se₂₁]Cl (3) and (Bmmim)₆[Mn(dien)₂]₂Sn₁₅Se₃₅ (4). Single-crystal X-ray diffraction analyses revealed that these compounds exhibit lamellar anionic [Sn₃Se₇]_n²ⁿ⁻ structures. [Sn₃Se₇]_n²ⁿ⁻ layers in all 1–4 possess a {6³} net, considering [Sn₃Se₁₀] semi-cube unit as a 3-connected node; however, diverse multi-membered rings exist there. In compounds 1 and 2, all the [Sn₃Se₁₀] units are 3-connected nodes interlinking with each other via edge-sharing two Se atoms to produce six-membered rings. However, in compound 3, the insertion of two [Sn₃Se₉] units into a six-membered ring results in a novel eight-membered heart-shaped ring, which has never been observed before in the family of chalcogenidostannates. More interestingly, the [Sn₃Se₇]_n²ⁿ⁻ layer in compound 4 consists of mixed six- and eight-membered rings. The phase composition is strongly dependent on the ratio of IL to MAC in the syntheses, e.g., 1 and 2 were obtained with IL : MAC ratios less than 3 : 1 and 4 : 1, while 3 and 4 were obtained when the ratios were increased to 4 : 1 and 5 : 1, respectively. The structural variation from 1 to 4 clearly indicates the competitive and synergistic effects between MAC and IL cation on the formation of lamellar selenidostannates. A synthetic approach via varying the ratio of IL to MAC cation as solvent and structure-directing agent will be attractive in the synthesis of novel chalcogenidometallates.