Anion and cation effects on imidazolium salt melting points: a descriptor modelling study.

The challenge of predicting the melting point of ionic liquids is outlined. A descriptor modelling approach for two separate sets of ionic liquids is presented. In each case, the cations and the anions are modelled separately, using quantitative structure-property relationships. Both models include constitutional, topological and geometric descriptors as well as quantum mechanical ones. This approach gives access to (nxm) ionic liquids using only (n+m) calculations. The protocol is tested and validated for predicting the melting points of two sets, comprised of 22 and 62 imidazolium-based ionic liquids, respectively. Good correlations and predictions are obtained in both cases. Within the data set selected (only monopositive and mononegative ions are studied, and so total charge was not a factor), the degree of sphericity is the most important variable for the anion, while for the cation the main descriptors pertained to three radial distribution functions that describe three different sections in the cation. These characterise the ionic interactions, the symmetry-breaking region, and the length of the side chains.

[1]  Ritu Jain,et al.  QSPR Correlation of the Melting Point for Pyridinium Bromides, Potential Ionic Liquids , 2002, J. Chem. Inf. Comput. Sci..

[2]  R. Singer,et al.  Ionic Liquids: The Neglected Issues , 2005 .

[3]  Alan R. Kennedy,et al.  Ionic liquid crystals: hexafluorophosphate salts , 1998 .

[4]  Hongyan He,et al.  Prediction of the melting points for two kinds of room temperature ionic liquids , 2006 .

[5]  C. Hardacre,et al.  Small-Angle X-ray Scattering Studies of Liquid Crystalline 1-Alkyl-3-methylimidazolium Salts , 2002 .

[6]  Roberto Todeschini,et al.  Handbook of Molecular Descriptors , 2002 .

[7]  Maykel Pérez González,et al.  In silico studies using Radial Distribution Function approach for predicting affinity of 1α,25-dihydroxyvitamin D3 analogues for Vitamin D receptor , 2006, Steroids.

[8]  João Aires-de-Sousa,et al.  Estimation of melting points of pyridinium bromide ionic liquids with decision trees and neural networks , 2005 .

[9]  Johann Gasteiger,et al.  Deriving the 3D structure of organic molecules from their infrared spectra , 1999 .

[10]  Robin D. Rogers,et al.  Ionic liquids as green solvents : progress and prospects , 2003 .

[11]  R. Sheldon,et al.  Biocatalytic transformations in ionic liquids. , 2003, Trends in biotechnology.

[12]  Roger A. Sheldon,et al.  Biocatalysis in ionic liquids. , 2002, Chemical reviews.

[13]  Paola Gramatica,et al.  3D-modelling and prediction by WHIM descriptors. Part 9. Chromatographic relative retention time and physico-chemical properties of polychlorinated biphenyls (PCBs) , 1998 .

[14]  Peter Wasserscheid,et al.  Ionic Liquids in Synthesis , 2002 .

[15]  F. Endres,et al.  Air and water stable ionic liquids in physical chemistry. , 2006, Physical chemistry chemical physics : PCCP.

[16]  K. R. Seddon,et al.  Nanoclusters in ionic liquids: evidence for N-heterocyclic carbene formation from imidazolium-based ionic liquids detected by (2)H NMR. , 2005, Journal of the American Chemical Society.

[17]  Gadi Rothenberg,et al.  Topological Mapping of Bidentate Ligands: A Fast Approach for Screening Homogeneous Catalysts , 2005 .

[18]  Martin A. Abraham,et al.  Clean solvents : alternative media for chemical reactions and processing , 2002 .

[19]  Robin D. Rogers,et al.  Ionic liquids : industrial applications for green chemistry , 2002 .

[20]  Robin D. Rogers,et al.  Ionic Liquids IIIB: Fundamentals, Progress, Challenges, and Opportunities: Transformations and Processes , 2005 .

[21]  Ruth Pachter,et al.  Prediction of Melting Points for Ionic Liquids , 2005 .

[22]  J. Dupont,et al.  Synthesis and Characterization of Pt(0) Nanoparticles in Imidazolium Ionic Liquids , 2006 .

[23]  M. Karelson,et al.  QSPR: the correlation and quantitative prediction of chemical and physical properties from structure , 1995 .

[24]  K. R. Seddon,et al.  The phase behaviour of 1-alkyl-3-methylimidazolium tetrafluoroborates; ionic liquids and ionic liquid crystals , 1999 .

[25]  M. Karelson,et al.  Quantum-Chemical Descriptors in QSAR/QSPR Studies. , 1996, Chemical reviews.

[26]  R. P. Swatloski,et al.  pH-Dependent partitioning in room temperature ionic liquids provides a link to traditional solvent extraction behavior , 2000 .

[27]  Frank Endres,et al.  Electrodeposition of nanoscale silicon in a room temperature ionic liquid , 2004 .

[28]  Erik Johansson,et al.  Multivariate design and modeling in QSAR , 1996 .

[29]  Ritu Jain,et al.  Correlation of the Melting Points of Potential Ionic Liquids (Imidazolium Bromides and Benzimidazolium Bromides) Using the CODESSA Program , 2002, J. Chem. Inf. Comput. Sci..

[30]  R. Pachter,et al.  Quantitative Structure-Property Relationships for Melting Points and Densities of Ionic Liquids , 2005 .

[31]  Suzanne Johnson,et al.  Crystal polymorphism in 1-butyl-3-methylimidazolium halides: supporting ionic liquid formation by inhibition of crystallizationElectronic supplementary information (ESI) available: packing diagrams for I and II; table of closest contacts for I, I-Br and II. See http://www.rsc.org/suppdata/cc/b3/b304 , 2003 .

[32]  Joan F. Brennecke,et al.  Predicting melting points of quaternary ammonium ionic liquids , 2003 .

[33]  大野 弘幸,et al.  Electrochemical aspects of ionic liquids , 2005 .

[34]  D. Macfarlane,et al.  Thermal Degradation of Ionic Liquids at Elevated Temperatures , 2004 .

[35]  Dan Hancu,et al.  Green processing using ionic liquids and CO2 , 1999, Nature.

[36]  K. R. Seddon,et al.  Crystal and liquid crystalline polymorphism in 1-alkyl-3-methylimidazolium tetrachloropalladate(II) salts , 2001 .