At 270/295 K the carbonate groups still hold the former low-temperature position to 60/46%, whereas 40/54% are disordered into at least two different positions with large and strongly smeared anisotropic displacement parameters of the carbonate O atoms. The CO3 position is constrained by hydrogen bonds, involving at least three H bonds per acceptor oxygen atom. The CO3 molecules are perfectly ordered at 110 K and show almost isotropic ADPs of the carbonate O atoms.

The structure is pseudo-centric, only the carbonate groups and four H atoms violating a centric symmetry. O⋯O > 2.73 Å) in a NaCl-like arrangement. These units are connected by hydrogen bonds (d The structure is composed of pairs of edge-sharing Na(H2O)6 octahedra forming Na2(H2O)10 units, and CO3 molecules. In contrast to the previous structure description, even the hydrogen atoms were located and refined with isotropic displacement parameters. Whereas the crystal structure of natron at room temperature had first been published in 1969 with R = 18%, in the present investigation the non-centrosymmetric structure was solved by direct methods and refined subsequently to R1 = 1.9% (110 K), 2.5% (270 K), and 3.5% (295 K).

A single-crystal fragment was measured on a CCD X-ray four-circle diffractometer at 110, 270 and 295 K. ♬rystals of natron, Na2CO3♱0H2O, were grown by slow evaporation of a saturated sodium carbonate solution at room temperature.

Natron nahco3