Compositional effects on Si-OH bond length in hydrous silicates with implications for trends in the SiOH acidity

作者：Zarubin Dmitri P^*

来源：Journal of Solid State Chemistry, 2014, 212: 30-36.

DOI：10.1016/j.jssc.2014.01.002

• Hydrogen silicate
• Bond length
• Bronsted acidity
• Silanol group
• Silica acidity

Theoretical calculations of the structure and Bronsted acidity of SiOH groups in silica clusters have never addressed the question if these vary with the degree of SiOH deprotonation. In this connection, a statistical analysis is presented of Si-OH bond lengths in crystalline hydrogen silicates with well-determined structures with a special emphasis placed on effects of the silicate composition. It is found that among hydrogen silicates of large cations with low charges the Si-OH bonds are always longer than terminal Si-O bonds in the same anion and correlate in length with the anionic charge per tetrahedron. The findings are explained by steric limitations on charge balancing at oxygen atoms by hydrogen bonds and/or cations. It is suggested that similar limitations and imbalances may underlie the well-known trends in the Bronsted acidity of silicic acids and silicas in aqueous media: decreased acidity with increased SiOH deprotonation and increased acidity with increased tetrahedra connectivity.

• 出版日期2014-4