Structural, spectroscopic, and computational studies on Tl4Si5O12: a microporous thallium silicate

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Thallium silicates are a class of inorganic compounds with potential applications in materials science.
• Understanding the crystal structure and properties of novel thallium silicates is crucial for exploring their functionalities.

Purpose of the Study:

• To synthesize and characterize single crystals of a previously unknown thallium silicate, Tl4Si5O12.
• To determine the crystal structure, including symmetry, space group, and unit cell parameters.
• To investigate the structural features, such as framework type, ring sizes, and cation coordination, and relate them to electronic properties.

Main Methods:

• Hydrothermal crystallization of a glassy starting material at 500 °C and 1 kbar.
• Single-crystal X-ray diffraction for structure analysis.
• Raman spectroscopy and Density Functional Theory (DFT) calculations for vibrational and electronic structure investigations.

Main Results:

• Successfully prepared single crystals of Tl4Si5O12 with monoclinic symmetry (space group C2/c).
• Classified the compound as an interrupted framework silicate with Q(3)- and Q(4)-units (2:1 ratio) and identified 4-, 6-, and 12-membered rings.
• Observed a framework density comparable to zeolitic materials and characterized the unique coordination of thallium cations, attributed to a stereochemically active lone pair.

Conclusions:

• The new thallium silicate, Tl4Si5O12, possesses a porous structure with channels suitable for cation location.
• The structural and electronic properties are influenced by the stereochemically active lone pair of thallium cations.
• Combined spectroscopic and computational methods provide a comprehensive understanding of the compound's vibrational and electronic behavior.