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

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) ų, 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) ų, 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) ų, 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) ų, 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.