M-Sn-Q (M = Zn, Cd; Q = S, Se) Compounds Templated by (Alkyl)ammonium Species: Synthesis, Crystal Structure, and Sr2+Adsorption Property

Deep investigations on the synthetic and structural chemistry of heterometallic chalcogenidostannates bear fundamental significance for the establishment of the structure-property relationship that would offer guidance on the functional material innovation. Presented here are four ammonium-and/or alkylammonium-directed M-Sn-Q (M = Zn, Cd; Q = S, Se) compounds, namely, [NH4]7[H3O]3Zn4Sn4S17 (1), [ N H4] 5 [ ( CH3)2NH2] Z n4S n5S1 7 (2), [CH3CH2NH3]22Zn16Sn12Se51(H2O)4 center dot 16H2O (3), and [NH4]2CdSnSe4 (4). All four compounds were synthesized in deep eutectic solvents (DESs) or ethylamine aqueous solution, both of which function simultaneously as reaction media and structure-directing agents. Compound 1 consists of discrete P1-[Zn4Sn4S17]10- clusters templated by mixed [NH4]+/[H3O]+ cations. In compound 2, such P1 clusters are bridged by Sn4+ ions in a 4,4-connection mode to form a [Zn4Sn5S17]n6n- framework with three types of cavities (I-III) varying in size. The two smaller cavities (I and II) accommodate NH4+while the larger one(III) is occupied by [(CH3)2NH2]+, reflecting the rational size-dependence of cations on cavities. Compound 3 features an [Zn16Sn12Se51(H2O)4]n22n- open framework constructed from the 4,3-connection of P1-[Zn4Sn4Se17]10- clusters and {Zn(H2O)}2+ bridges. This linkage mode contributes to a large cage-like subunit (inner dimension: 21.99 x 9.06 angstrom 2) and therefore an ultrahigh porosity that are occupied by [CH3CH2NH3]+ cations and water molecules (volume fraction: 57.7%). Compound 4 exists as a stacking of [CdSnSe4]n2n- chains, which are composed of alternatively arranged {CdSe4} and {SnSe4} tetrahedra, in combination with [NH4]+ cations as both charge-compensating and space-filling agents. Detailed synthetic, structural, and topological analyses were performed on these solid materials, coupled with extensive investigations on their optical and thermal properties. Compound 3 exhibits an efficient Sr2+ adsorption performance, featuring ultrafast kinetics (94.69% in 5 min), high removal rate (98.57% in 20 min) at equilibrium, and high capacity (104.17 +/- 23.53 mg g-1).