X-Ray crystal structure of the industrial bleaching agent ‘sodium percarbonate’[sodium carbonate–hydrogen peroxide (2/3)]

Abstract

The title compound crystallises in the orthorhombic system. wrth unit-cell dimensions a= 9.183(1), b= 15.745(1), c= 6.730(1)Å, space group Aba2, and Z= 8. Diffractometer data have been used to solve the structure, and least-squares refinement with 486 independent reflections has reached R 0.029. Apart from sodium and carbonate ions. the structure determination has shown the presence of hydrogen peroxide molecules which are hydrogenbonded to the carbonate ions, and therefore the compound is not a true ‘percarbonate.’ Within a strictly ordered ionic environment, the two crystallographically independent hydrogen peroxide sites show disorder. The molecules in the two types of sites are appreciably different. Thus eight molecules in the unit cell are skewed with a dihedral angle (ϕ) of ca. 125°, while the other four appear to be nearly planar (ϕ ca. 170°). Infrared and Raman studies on the normal and ¹³C and ²H isotopically substituted forms of the compound also suggest that there are two types of H₂O₂, one being nearly planar and the other skewed.