<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Single crystals of Rb<sub>2</sub>H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>·2H<sub>2</sub>O are obtained from an equimolar aqueous solution of H<sub>4</sub>P<sub>2</sub>O<sub>6</sub> and Rb<sub>2</sub>CO<sub>3</sub> at 4 °C.</p> </abstract>