Thioaluminogermanate M (AlS₂)(GeS₂)₄ (M = Na, Ag, Cu): Synthesis, Crystal Structures, Characterization, Ion-Exchange and Solid-State ²⁷Al and ²³Na NMR Spectroscopy

The new thioaluminogermanate Na(AlS₂)(GeS₂)₄ (1) was successfully synthesized by a direct combination reaction. The compound crystallizes in the monoclinic space group P2₁/n (no. 14) with unit cell parameters a = 6.803(3) Å, b = 38.207(2) Å, c = 6.947(4) Å, and β = 119.17(3)°. The crystal structure is composed of a [(AlS₂)(GeS₂)₄]^- 3D polyanionic network, in which Al and Ge atoms share the atomic positions and Na cations occupy the channels and voids formed by the connection of (Ge/Al)S₄ tetrahedra. The title compound shows a cation-exchange property with monovalent Ag⁺ and Cu⁺ ions at room temperature in solvent media, resulting in the formation of the isostructural compounds Ag(AlS₂)(GeS₂)₄ (2) and Cu(AlS₂)(GeS₂)₄ (3), respectively. The ion-exchange products Ag(AlS₂)(GeS₂)₄ (2) and Cu(AlS₂)(GeS₂)₄ (3) show higher air stability and narrower bandgap energies compared to those of the parent compound Na(AlS₂)(GeS₂)₄ (1).