The crystal structures of solvent-free alkali-metal squarates from powder diffraction data

Abstract

Abstract The crystal structures of solvent-free lithium, sodium, rubidium, and cesium squarates have been determined from high resolution synchrotron and X-ray laboratory powder patterns. Crystallographic data at room temperature of Li2C4O4: a = 7.1073(3) Å, b = 9.5627(4) Å, c = 3.2973(1) Å, β = 101.11(1)°, V = 219.91(1) Å3, monoclinic, C2/m, Z = 2, Na2C4O4: a = 3.4925(1) Å, b = 6.8152(1) Å, c = 10.3525(2) Å, β = 91.56(1)° V = 246.32(1) Å3, monoclinic, P21/c, Z = 2; Rb2C4O4: a = 10.7908(5) Å, b = 6.8494(3) Å, c = 4.4521(2) Å, β = 92.39(0), V = 328.77(4) Å3, monoclinic, C2/m, Z = 2; Cs2C4O4: a = 11.1768(3) Å, b = 7.0453(2) Å, c = 4.7424(1) Å, β = 92.89(1)°; V = 372.97(4) Å3, monoclinic, C2/m, Z = 2. The packing features of lithium squarate can be deduced from the AlB2 structure type, while sodium, rubidium, and cesium squarate are related to the CdI2 type. The relation between the two types of crystal structures of the squarate dianion is discussed.