Abstract
The structure of the title compound, [K2(C4H7O2)2(H2O)] n , is composed of stacked sandwiches, which are formed by cation-oxygen bilayers surrounded by methyl-ethyl hydro-phobic chains. These sandwiches are held together by van der Waals inter-actions between the methyl-ethyl groups. The methyl-ethyl groups are disordered over two positions with occupancies 0.801 (3):0.199 (3). The potassium cations are coordinated by seven O atoms, which form an irregular polyhedron. There is a water mol-ecule, the oxygen atom of which is situated in a special position on a twofold axis (Wyckoff position 4e). The water H atoms are involved in Owater-H⋯Ocarbox-yl hydrogen bonds of moderate strength. These hydrogen bonds are situated within the cation-oxygen, i.e. hydro-philic, bilayer.
Highlights
The structures of simple alkali 2-methylpropanoates have not been determined so far
The phases of isobutyrate salts are supposedly prone to undergo phase transitions due to the ordering of voluminous hydrophobic methylethyl chains by analogy to the phase transitions observed in alkali propionates and 2-methylpropanoates (Ferloni et al, 1975)
A rather tedious structure determination can be expected in alkanoates where the number of carbon atoms is greater than two because the organic chains tend to be positionally disordered and tend to exert large thermal agitation
Summary
The structures of simple alkali 2-methylpropanoates (isobutyrates) have not been determined so far (as shown by a search of the Cambridge Structural Database, version 5.41, update of November 2019; Groom et al, 2016). The structure determinations of 2-methylpropanoates as well as those of chemically related compounds with carboxylates other than the formates and acetates show that their structures share the same tendency for the separation of metal cations, carboxylate groups and sometimes water molecules on the one hand from the organic chains on the other. The former groups are hydrophilic while the latter are hydrophobic. Standing the structural features in simple alkali carboxylates with CnH2n+1COOÀ, n > 2, and related structures
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