Acid-Induced Conversions in Open-Framework Semiconductors: From Cd4Sn3Se136- to Cd15Sn12Se4614-, a Remarkable Disassembly/Reassembly Process

摘要

The assembly of chalcogenides with 3D open frameworks is of considerable scientific interest because, like the zeolites, they have large free spaces. Yet due to their greater chemical, compositional, and structural diversity, the chalcogenides present a wider variety and broader scope of properties. These materials can be relevant in molecular recognition,2a ion conduction,3c environmental remediation, and photocatalysis. The chalcogen elements can impart novel photonic or electronic properties that are not found in zeolites.3 However, the ability of zeolites (for example, H-Y, H-ZSM-5) to act as solid-acid catalysts is not shared by open-framework chalcogenides, because the chalcogenides are more vulnerable to attack by acid. The 3D open framework of K6Cd4Sn3Se13 contains intersecting tunnels that enable fast ion exchange with alkali-metal cations. The observation of efficient ion exchange in K6Cd4Sn3Se13 led to our idea of making proton-exchanged H6Cd4Sn3Se13, which would contain alkali-metal-free tunnels, through the direct reaction of K6Cd4Sn3Se13 with acid. Our attempt to make H6Cd4Sn3Se13 led to the generation of the new 3D anionic framework Cd15Sn12Se4614-, which shows surprising resistance to acids, as well as excellent ion-exchange properties. Although the number of open-framework chalcogenides has been steadily increasing, reactivity studies on these materials have not been emphasized to date. Herein, we give one of the first reports on the reactivity of these compounds.