Crystal data for potassium and rubidium propanoates: C₂H₅COOK and C₂H₅COORb

Powder patterns are reported for all the phases stable between 130 K and the melting points. Potassium propanoate, K⁺.C₃H₅O₂, is monoclinic between 258 and 353 K [a = 3.971 (3), b = 5.799 (4), c = 11.476 (7) Å, β = 91.42 (1)° at 322.0 K] and orthorhombic at higher temperatures [a = 4.051 (5), b = 5.772 (7), c = 11.706 (15) Å at 414.0 K]. Rubidium propanoate, Rb⁺.C₃H₅O₂, shows two orthorhombic phases above 317 K: a = 4.235 (2), b = 5.951 (3), c = 11.557 (6) Å at 371.5 K and a = 4.335 (2), b = 5.920 (3), c = 11.767 (5) Å at 573.2 K.