Layered alkali propanoatesM+(C2H5COO)−;M+= Na+, K+, Rb+, Cs+

Abstract

The title alkali propanoates poly[(μ5-propanoato)alkali(I)],M+(C2H5COO)−, 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 hydrophobic layers composed of dangling ethyl chains from the carboxylate 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 carboxylate anion, while each of the other four oxygen atoms belongs to different carboxylate groups, which are in a bridging monodentate mode. Despite the close similarity, each of the studied alkali propanoates crystallizes in a different space group. The atoms are in general positions, except for the cation in K+(C2H5COO)−, 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+propanoates, in contrast to the Rb+and Cs+propanoates. 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 theaunit-cell parameter of the Na+compound with respect to that of the K+compound, otherwise the structures are homeotypic. In Cs+propanoate, a disorder of the methyl H atoms is observed.