Cation symmetry

Reduction in cation symmetry (ideally to Cl) lowers the freezing point and markedly expands the range of room-temperature liquid salts. Table 3.1-4 shows the effect of symmetry for a series of [NR4]X salts, in which all the cations contain 20 carbon atoms in the allcyl substituents [44]. 

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Table 3.1-4 Effects of cation symmetry on the melting points of isomeric tetraalkylammonium salts. In each case the cation (designated [N op] ) has four linear alkyl substituents, together containing a total of 20 carbons. Salts that are liquid at room temperature are indicated by /.

WIU1AM L JORGENSEN AND LIONEL SALEM 37. Cyclopropenium Cation Symmetry D3h... 

By X-ray crystallography it was shown that the monoclinic red-black crystals of Se6IAsF6 contain the homocyclic Se6I+ cation (symmetry C8 (87). The exocyclic iodine atom bridges neighboring See rings, the two Sel distances (273.6 pm) being equivalent and of bond order 0.5 (see Fig. 11). 

ILs viscosity iuCTeased when the chain lengA of the side chain increases, the side chain is composed of fluoride or an imidazole ring in position 2 methylation, or there is increased cation symmetry. Generally, when the cation is composed of the thermally stable imidazolium ion, the anion determines the thermal stability of the entire IL, increasing in the order TfjN >BF >PF ">halogen ions. Minami et al. [18] studied thermo-oxidative stability and volatility of ILs and found that ILs have greater thermal stability than conventional synthetic lubricants. It was also found that the stability of an ILs depends on the structures of both the anion and the cation. For example, the stability of 1, 3-dialkyl-imidazoUum is more stable than quaternary ammonium. 

Most of these methods are based on correiations of the observed equilibrium constant with properties like atomic number of the cation, type of cation, type of anion, type of ligand, p T of the ligand if it is a weak acid or weak base, crystallographic radii, solvated radii, electrostatic interaction energies, ionisation energies of the cation, symmetry of the ligand and more exotic properties. 

Note that as we change crystal structures in the other alkaline earth pyrophosphates, changes in lattice symmetry, and cation coordination occur, even though the local cation symmetry remains the same, i.e.- Ci =... 

Xiao, D., Hines, L.G.J., Li, S., Bartsch, R.A., Quitevis, E.L., Russina, O. and Triolo, A., Effect of cation symmetry and allq l chain length on the structure and intermolecular dynamics of 1,3-diallqrlimidazolium bis(trifluoromethanesulfonyl)ainide ionic liquids, J. Phys. Chem. B 113, 6426-6433 (2009). 

Rocha M, Neves CMSS, Freire MG, Russina O, Triolo A, Coutinho JAP, Santos LMNBF (2013) Alkylimidazolium based ionic liquids impact of cation symmetry on their nanoscale structural organization. J Phys Chem B 117 10889-10897... 

Effect of cation symmetry and alkyl chain length on the structure and intermolecular dynamics of 1,3-dialkylimidazolium... 

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