Layered alkali propano-ates M + (C 2 H 5 COO) - ; M + = Na + , K + , Rb + , Cs .

The title alkali propano-ates poly[(μ ₅ -propano-ato)alkali(I)], M ⁺ (C ₂ H ₅ COO) ^- , with alkali/ M ⁺ = Na ⁺ , K ⁺ , Rb ⁺ and Cs ⁺ , show close structural similarity, which is manifested by the coordination of the cations by six oxygen atoms in a chessboard motif, forming a bilayer. This bilayer is situated between hydro-phobic layers composed of dangling ethyl chains from the carboxyl-ate groups. Stacking of these two-dimensional sandwiches, which are parallel to (001), forms the title structures. Each metal cation is coordinated by six O atoms in the form of a distorted trigonal prism. One pair of these oxygen atoms belongs to a bridging, bidentately coordinating carboxyl-ate anion, while each of the other four oxygen atoms belongs to different carboxyl-ate groups, which are in a bridging monodentate mode. Despite the close similarity, each of the studied alkali propano-ates crystallizes in a different space group. The atoms are in general positions, except for the cation in K ⁺ (C ₂ H ₅ COO) ^- , which is situated on a mirror plane. Positional disorder of the methyl groups that are disordered over two positions is present in the Na ⁺ and K ⁺ propano-ates, in contrast to the Rb ⁺ and Cs ⁺ propano-ates. In the Na ⁺ compound, the occupational parameters of the disordered methyl groups are different compared to the K ⁺ compound where they are equal. This difference results in doubling of the a unit-cell parameter of the Na ⁺ compound with respect to that of the K ⁺ compound, otherwise the structures are homeotypic. In Cs ⁺ propano-ate, a disorder of the methyl H atoms is observed.
(© Fábry and Samolová 2020.)