Carbonate hydrates of the heavy alkali metals: Preparation and structure of Rb2CO3 center dot 1.5 H2O and Cs2CO3 center dot 3H(2)O

Rb2CO3 . 1.5 H2O and Cs2CO3 . 3 H2O were prepared from aqueous solution and by means of the reaction of dialkylcarbonates with RbON and CsOH resp. in hydrous alcoholes. Based on four-circle diffractometer data, the crystal st ructures were determined (Rb2CO3 . 1.5 H2O: C2/c (no.15), Z = 8, a = 1237.7 (2) pm, b = 1385.94(7) pm, c = 747.7(4) pm, beta = 120.133(8)degrees, V-EZ = 1109.3(6) . 10(6) pm(3); Cs2CO3 . 3 H2O: P2/c (no. 13), Z = 2, a = 654.5( 2) pm, b = 679.06(6) pm, c = 886.4(2) pm, beta = 90.708(14)degrees, V-EZ = 393.9(2) 10(6) pm(3)). Rb2CO3 . 1.5 H2O is isostructural with K2CO3 . 1.5 H 2O. In case of Cs2CO3 . 3 H2O no comparable structure is known. Both struct ures show (1)(infinity)[(CO32-)(H2O)]-chains, being connected via additiona l H2O forming columns (Rb2CO3 . 1.5 H2O) and layers (Cs2CO3 . 3 H2O), respe ctively.