StructuralCharacterization of 1,1,3,3-Tetramethylguanidinium Chloride IonicLiquid by Reversible SO2Gas Absorption.

A uniquenew ionic liquid–gas adduct solid state compound formed between1,1,3,3-tetramethylguanidinium chloride ([tmgH]Cl) and sulfur dioxidehas been characterized by X-ray diffraction and Raman spectroscopy.The structure contains SO2molecules of near normal structurekept at their positions by Cl–S interactions. The crystalsbelong in the orthorhombic system, space group Pbcn, with unit cell dimensions of a= 15.6908(10) Å, b= 9.3865(6) Å, and c= 14.1494(9)Å, angles α = β = γ = 90°, and Z= 8 at 120 K. The [tmgH]Cl has a very high absorptioncapacity of nearly 3 mol of SO2per mol of [tmgH]Cl at1 bar of SO2and at room temperature. However, part ofthe absorbed SO2was liberated during the crystallization,probably because the crystal only accommodates one molecule of SO2per [tmgH]Cl. The nature of the high absorption capacityof [tmgH]Cl as well as of the homologous compounds with bromide andiodide are discussed. Some of these salts may prove useful as reversibleabsorbents of SO2in industrial flue gases. [ABSTRACT FROM AUTHOR]