Pseudo-micropores formed by one-dimensional framework with hydrogen bonding in CsHSi2O5 observed by synchrotron powder diffraction and solid-state MAS NMR

Abstract

One-dimensional fibrous low dimensional caesium silicate, LDS-1, was synthesized by performing solid-state reactions with dry gels of silica containing tetrabutylammonium and caesium cations. We report the detailed crystal structure of LDS-1 comprising alternating alignments of zigzagged frameworks with four-membered rings and strong hydrogen bonds between adjacent terminal silanols; this structure is very similar to that of CsHSi₂O₅, whereas their crystal symmetries are different. The chain-like frameworks with a Q³ ((SiO)₃SiOH) local structure form an elliptical topology with pseudo-micropores by strong hydrogen bonding. The hydrogen bonding was clearly observed in the electron density distributions analyzed by the maximum entropy method using high-resolution synchrotron powder diffraction data. Solid-state MAS NMR spectroscopy also exhibits strong hydrogen bonding between adjacent oxygen atoms, as indicated by an atomic distance of d(O–O) ≈ 2.45 Å. The elliptical spaces hold large caesium cations.