Accessibility of Lithium Cations in VSH-2 Zeotype: Structural Effects and Formation of Protonated Water Clusters

The accessibility of lithium cations in microporous vanadosilicate VSH-2Cs of composition Cs-2(VO)(Si6O14) center dot 3H(2)O was investigated by Single Crystal X-ray Diffraction, Attenuated Total Reflection Fourier Transformed Infrared Spectroscopy and Density Functional Theory calculations. The topological symmetry of VSH-2Cs is described in space group Cmca. After Li-ion exchange, the structure of VSH-2Li adopted monoclinic symmetry (space group C2/c) with a= 17.011(2) angstrom, b= 8.8533(11) angstrom, c= 12.4934(16) angstrom, ss= 91.677(4)degrees, V= 1880.7(4) angstrom(3). The strong interactions between Li ions and oxygen-framework atoms drive the main deformation mechanism, which is based on cooperative rotation of SiO4 and VO5 units around their oxygen atoms that behave as hinges. Exchange of Cs+ by Li+ is incomplete and accompanied by the formation of protonated species to counterbalance the electrostatic charge. The incorporation of protons is mediated by the presence of water dimers in the structural channels. H2O molecules in VSH-2Li account not only as '' space-fillers '' after the removal of large Cs ions but also mediate proton transfer to compensate the negative charge of the host vanadosilicate framework.

Automated summary

The accessibility of lithium cations in microporous vanadosilicate VSH-2Cs was investigated, and the main deformation mechanism driven by strong interactions between Li ions and oxygen-framework atoms was revealed.