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 Se^2-ions to Se₂^2- 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.