A mixed molecular salt of lithium and sodium breaks the Hume-Rothery rules for solid solutions

The first molecular solid solution of lithium and sodium ions is reported. In spite of the different chemical and structural properties of the parent compounds, the two cations form a homogeneous mixed phase with the isoorotate ion. Such observation appears in contrast with the Hume-Rothery principles for solid solutions. Furthermore the mixed salts in the series are thermally stable up to 100 °C and non-hygroscopic, which makes them relevant for their potential use as a lithium drug substance. Despite the difference in size and chemistry, lithium and sodium form a solid solution as isoorotate salt. Such behaviour, which represents an exception to the Hume-Rothery rules, can be exploited in the preparation of novel lithium drugs.