Na2Si3O7: an incommensurate structure with crenel-type modulation functions, refined from a twinned crystal

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Crystallography

Background:

• Previous studies incorrectly assigned an orthorhombic space group to Na(2)Si(3)O(7).
• Understanding the precise crystal structure is crucial for its properties and applications.

Purpose of the Study:

• To accurately determine the crystal structure of metastable, incommensurately modulated sodium silicate (Na(2)Si(3)O(7)).
• To clarify the structural discrepancies with prior investigations.

Main Methods:

• Single-crystal X-ray diffraction.
• Analysis using (3 + 1)-dimensional superspace symmetry.
• Application of crenel-type modulation functions.

Main Results:

• The compound crystallizes in a monoclinic system with a pseudo-orthorhombic cell and exhibits twinning.
• An aperiodic sequence of silicate chains is described using modulation functions.
• Sodium cations link [Si(3)O(7)](2-) layers, with distortions in silicate tetrahedra.

Conclusions:

• The correct crystal structure of Na(2)Si(3)O(7) is established as monoclinic, resolving previous ambiguities.
• The study provides detailed insights into silicate chain modulation and cation coordination.
• Crystal chemical relationships to other sodium and lithium silicates are elucidated.