Ionic liquids (ILs) are organic salts with low melting points and high thermal stability. Due to their
other unique properties, such as high chemical stability, non-flammability, and low toxicity, ILs are being
considered as greener alternatives of conventional organic solvents[1]. Recent applications of
tetramethylguanidinium [TMG] based ILs in the absorption of flue gases have led to an increasing demand
for these ILs. Also studies on the structural properties of these ILs, therefore, gained recent attention to get
a better understanding of the reasons for the apparent affinity to absorb the gases[2]. Crystallization of
ionic liquids [ILs], is of great interest for determining the crystal structure and molecular interactions.
Hydrogen bonding is an important non-covalent interaction, which is related to the properties of ILs. The
importance of hydrogen bonding in ionic liquids (ILs) is critical for the understanding of the modes of
inter-action and conformational influences of IL cations and anions and their general behavior [3]. The Xray
crystal structure of ILs is difficult to study, as they are in the liquid state at room temperature and it is a
challenging task to crystallize them. A modern day technique is used now-a-days for structure
determination of compounds with low melting points by in situ crystallization using optical heating and
crystallization device (OHCD)[4].
In this work, we report the synthesis and characterization of tetramethylguanidinium [TMG] cation based
ILs with different carboxylic acid as anion and the crystal structure of these ILs were determined at low
temperature to understand the interactions and their network formation. Using Hirshfeld surface analysis[5]
the intermolecular interactions in crystal packing of ILs were analyzed and quantified. The
physicochemical properties such as density (ρ), speed of sound (u) viscosity (η) and refractive index (nD)
values were measured as a function of temperature over the range from 293.15 K to 343.15 K at
atmospheric pressure (0.1 MPa). CO2 absorption capacity was studied for even number carboxylic acid
anions TMG][But], [TMG][Hex] and [TMG][Oct].The maximum absorption capacity of CO2 was observed
for [TMG][Oct], which clearly indicated that the increase in chain length increases the absorption capacity.
REFERENCES
1 . N. V. Plechkova and K. R. Seddon, Chem. Soc. Rev., 2008, 37, 123–150.
2. R. W. Berg et al., J. Phys. Chem. B, 2009, 113, 8878–8886.
3. Christian Roth et al., Angew. Chem. Int. Ed, 2010, 49, 10221–10224.
4. Boese, R. Zeitschrift fur Kristallographie - Crystalline Materials 2014, 229 (9), 595–601.
5. Macrae, C. F. et. al., J. Appl.Crystallogr. 2006, 39, 453–457.