Synthesis, structure and properties of CsHSi3O7, a layered silicate with a chiral structure

The chiral layered silicate CsHSi₃O₇ has been synthesized by hydrothermal techniques, and its structure determined by single crystal X-ray diffraction. The compound crystallizes in the space group P2₁2₁2₁. The silicate single layer consists of both four- and three-connected SiO₄ tetrahedra and may be considered as a member of a series of layer structures with the general formula (Si₄O₉)_m(Si₂O₅)_n. Strong hydrogen bonds occur between the terminal OH⁻ and O²⁻ ions of neighboring layers. The Cs⁺ cations can be ion-exchanged by protons to give a phase of composition H₂Si₃O₇·H₂O with a water molecule occupying the original Cs position, as confirmed by single crystal X-ray diffraction data. The water molecule in H₂Si₃O₇·H₂O can be readily removed without collapse of the crystal structure. Both CsHSi₃O₇ and H₂Si₃O₇·H₂O show SHG (second harmonic generation) efficiencies comparable to that of quartz, and both are not phase-matchable materials.