Di‐ and Tricationic Organic Salts: An Overview of Their Properties and Applications

Abstract

During recent years growing interest has been devoted to the synthesis and applications of polycationic organic salts. Among them, di‐ and tricationic organic salts can be considered the natural evolution of monocationic ones. These last have given rise to the large class of ionic liquids. In the cases of di‐ and tricationic organic salts, the potential to change their structural features simply by varying the properties either of the charged heads or of the spacers separating them provides the opportunity to obtain materials suitable for different applications. This review article highlights recent progress in the study of the properties of di‐ and tricationic organic salts, as well as in some of their uses as solvent systems, receptors for anion recognition, ionic liquid crystals, low‐molecular‐weight gelators, additives for dye‐sensitized solar cells, and so on.

Liquid crystals based on silver carbene complexes derived from dimeric bis(imidazolium) bromide salts

“…Repetead recrystallisations from a mixture of dichloromethane and ethyl ether, accompanied by charcoal decolorisation to remove the silver excess, gave the desired compounds as white or light yellow-brown products. Indeed, the 10 1 H-NMR spectroscopy showed no signal higher than 8 ppm, confirming the successful deprotonation of the carbenic protons of bis(imidazolium) 2a-c salts. In the absence of X-ray structural studies on single-crystal and based on NMR and IR spectroscopy data together with elemental analysis results, these silver 15 complexes can be described by a [Ag 2 (NHC)Br 2 ] general formula, while the existence of a polymeric structure similar to the one described by Chiu et al 23 could not be ruled out.…”

“…Powder Xray diffraction studies were performed on cooling the samples from the isotropic liquid to the mesophase with the exception of 5 cholesteryl-based compounds, 2c and 3c, when the isotropic state could not be reached due to some decomposition at temperatures above 135 o C. For these two compounds the powder X-ray patterns were recorded on heating, before reaching the decomposition temperatures. All silver complexes show 10 diffraction pattern typically observed for mesophases in the temperature range of liquid crystal phase and frozen, glassy mesophases. The powder X-ray diffraction data for componds 2ac and the related silver carbene complexes are shown in Table 2.…”

“…Mesophases were assigned by their optical texture and powder X-ray diffraction data. The powder X-ray diffraction measurements were made on a D8 Advance diffractometer (Bruker AXS GmbH, Germany), in 10 parallel beam setting, with monochromatised Cu-K α1 radiation (λ=1.5406 Å), scintillation detector, and horizontal sample stage. The measurements were performed in symmetric (θ-θ) geometry in the 2θ range from 1. control of the samples during measurements was achieved by adapting a home-made heating stage to the sample stage of the diffractometer.…”

Synthesis of tetracationic organic salt from 4,4'-bipyridine

“…These have been widely used as alternative reaction media to conventional organic solvents [4][5][6] and in electrochemistry [7,8]. Evolved from the latter, di-, tri-and tetracationic organic salts have become ideal materials in solving several problems [9]. This is due to the potential to change their structural features simply by: varying the nature of the cation and/or the anion; tuning them by introducing small structural changes in the constituting ions, or of the spacers separating them provides the opportunity to obtain materials with sets of desired properties suitable for different applications.…”

“…This is due to the potential to change their structural features simply by: varying the nature of the cation and/or the anion; tuning them by introducing small structural changes in the constituting ions, or of the spacers separating them provides the opportunity to obtain materials with sets of desired properties suitable for different applications. They have been applied as a chemical anchorage on a solid support [10], starting materials for the synthesis of molecular devices [11,12], reaction media or catalysts, immobilization of catalysts [9], reaction media for high-temperature organic reactions [13,14], catalysts [15], receptors for anion recognition [16], low-molecular-weight gelators [17], fluorescent organic salts [18,19], energetic materials [20,21], for use in the preparation of solid films for organic electronic applications [22] and electrowetting materials [23]. Heteromolecules including imidazole, 1,10-phenanthroline, pyridine and others have been used as the starting materials for the synthesis of polycationic organic salts.…”