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

• Main Authors: Jan Fábry, Erika Samolová
• Format: Article
• Language: English
• Published: International Union of Crystallography 2020-09-01
• Series: Acta Crystallographica Section E: Crystallographic Communications
• Subjects: crystal structure; hydrogen bonding; carboxylates; the cambridge structural database; positional disorder; occupational disorder
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S2056989020011469

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 the a unit-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.