Redox-Induced “Zipper” Action in Rb2Bi4Se7 and Cs2Bi4Se7: Coupling of Slabs to a Three-Dimensional Framework through Single-Crystal to Single-Crystal Conversion

An unprecedented and remarkable redox transformation occurs in Rb2Bi4Se7 and Cs2Bi4Se7 in the solid state. The process involves the topotactic oxidative coupling of entire rows of Se2− ions to Se groups in a cooperative way reminiscent of the closing action of a zipper (see figure). This process happens over all the single crystals. It involves the rapid expulsion of alkali ions from the crystals and results in the daughter compounds RbBi4Se7 and CsBi4Se7 in which the original slabs are stitched into a three-dimensional net.