The crystal structure of [delta]-Na[sub 2]Si[sub 2]O[sub 5]

The crystal structure of [delta]-Na[sub 2]Si[sub 2]O[sub 5] has been solved and refined to an R index of 0.053 for 933 independent reflections. The compound is monoclinic with space group P2[sub 1]/n (a = 8.393(2) [angstrom], b = 12.083(3) [angstrom], c = 4.843(1) [angstrom], [beta] = 90.37(3)[degree], V = 491.1(1) [angstrom][sup 3], M[sub r] = 182.15 u, Z = 4, [lambda](MoK[alpha]) = 0.71073 [angstrom], D[sub x] = 2.46 g/cm[sup 3], [mu](MoK[alpha]) = 8.3 cm[sup [minus]1]). The crystal showed twinning by pseudomerohedry according to 2[sub 100], a feature which the authors took account of in the refinements. The compound belongs to the group of single layer silicates. Individual sheets can be described as being built by the condensation of zweier single chains of SiO[sub 4] tetrahedra parallel to the c-axis or, alternatively, by condensation of vierer single chains parallel to the a-axis. The stacking of the layers parallel to the b-axis results in a three-dimensional structure in which the sodium cations reside between the layers for charge compensation.