Syntheses and Crystal Structures of New Quaternary Ag-Containing Group 5 Chalcogenides: KAg₂M^VSe₄ and K ₃Ag₃M^V₂S₈ (M^V = Nb, Ta)

Four new quaternary Ag-containing group 5 chalcogenides, KAg ₂NbSe₄ (1), KAg₂TaSe₄ (2), K ₃Ag₃Nb₂S₈ (3), and K ₃Ag₃Ta₂S⁸ (4), have been prepared through the use of molten alkali metal polychalcogenides as reactive fluxes and structurally characterized by single-crystal X-ray diffraction techniques. The layer-type structures of 1 and 2 can be regarded as constructed from the basic building block of the incomplete cubane [Ag₃M^VSe ₃], which are corner-shared to form an infinite chain along the a direction. These incomplete cubane chains are interconnected and further bridged by Se atoms along the c direction, leading to a two-dimensional structure. The crystal structure of 3 and 4 consists of one-dimensional triple-metal [Ag₃M^V₂S⁸] ^3- anionic chains seperated by K⁺ cations. The alternate packing of M^VS₄ and AgS₄ tetrahedra via edge-sharing along the b direction leads to mixed-metal sub-chains, every two of which are further linked by AgS₄ tetrahedra along the a direction through edge-sharing to the M^VS₄ tetrahedra, thus yielding the so-called triple-metal chains.