A charge transfer salt consisted of bis(maleonitriledithiolato)zincate dianion and 1,1'-didecyl-4,4'-bipyridinium exhibiting uncommon nematic mesophase behavior

Ionic Liquid Crystals: Versatile Materials

“…We would like to emphasize that many compounds that have been discussed in previous sections could also be termed "ISA compounds", in the sense that a charged functional component is converted into a LC material by combining it with a suitable, oppositely charged building block. This is, for example, the case for the [Eu(tta) 4 ] − , 122 [UO 2 Br 4 ] 2− , 115,116 438 and [Ni(mnt) 2 ] −870 metal complexes; redox-active ionic 4,4′-bipyridinium complexes with sulfonate surfactant molecules; 162,904,905 luminescent LC 1,10-phenanthrolinium compounds with a central propylene or ethylene bridge and with sulfate and sulfonate counterions; 161 and the thermotropic ionic LC receptor−anion complexes of the Maeda group. 391,420,985,989−993 A possible cooperative binding mechanism, which should be typical for ISA (see section 4.1; particularly in cases involving polyelectrolytes), was however not investigated in these reports, but one could argue that this can also be said about many reports focused specifically on socalled "ISA materials".…”

“…In continuation of their work on ionic compounds with a metal-containing anion with maleonitriledithiolato ligands (see section 8.1, 247), Ren and co-workers prepared a 1,1′-bis(nd e c y l ) -4 , 4 ′ -b i p y r i d i n i u m s a l t w i t h t h e b i s -(maleonitriledithiolato)zincate(II) ([Zn(mnt) 2 ] 2− ) anion (300). 438 This is a 2-fold negatively charged anion, which can form a 1:1 complex with the 4,4′-bipyridinium cation. In contrast to [Ni(mnt) 2 ] − , the [mnt] 2− ligands are tetrahedrally coordinated to the zinc(II) center in [Zn(mnt) 2 ] 2− , so that it is not a flat anion.…”

“…115 Ren and co-workers reported on the nonmetal-centered luminescence by a 1,1′-bis(n-decyl)-4,4′-bipyridinium salt with the bis(maleonitriledithiolato)zincate(II) ([Zn(mnt) 2 ] 2− ) anion (300). 438 Ziessel, Camerel, and co-workers synthesized SmA-and Col hex -forming photoluminescent tris(8-hydroxyquinoline-5sulfonato)aluminum(III) complexes (385-(cation + ) 3 ). 1004 Their work nicely illustrates the use of ISA to transform watersoluble fluorophores into compounds that are soluble in nonpolar volatile organic solvents.…”

“…This is not only due to the “straightening” of these chains by metal ion complexation; the stacking into columns also originates from the sequential electrostatic interactions between the ionic moieties in the direction of the columnar axes. Nevertheless, several examples of low molar mass thermotropic ILCs displaying a nematic phase, or a (not commonly observed) columnar nematic phase, can be found in the literature. ,,,,,− [Remark: The quaternary ammonium halide salts based on tris­( n -octadecyl)­amine that were originally claimed to show a nematic phase were later reported to show a SmA phase. , ] Veber and co-workers proposed that the formation of the N C phase by some tricatenar dithiolium salts can be rationalized by the fact that the columns in the lower-temperature Col hex and Col rec phases are stabilized by ionic interactions, so that the 2D hexagonal lattice can “melt” without complete destruction of the columns. , Several neutral nematogenic calamitic LCs with a crown ether moiety and/or short oligo­(ethylene oxide) chains were found to dissolve large amounts of LiBF 4 , NaOTf, or sodium picrate (with complexation of the alkali metal cations by the crown ether moiety if present) and still exhibit a nematic phase. − On the other hand, mesomorphism was lost upon addition of small amounts of LiBF 4 to some derivatives with a lower shape anisotropy . Yoshio et al mentioned a short-range nematic phase for an equimolar mixture of an IL ([C 2 mim]­[BF 4 ]) with a neutral, hydroxyl-terminated LC .…”

Ionic Liquid Crystals Based on Pyridinium Salts

“…Moreover, the nematic phase is commonly used in electrooptical devices. The nematic phase is quite rare in the case of ILCs, several examples have been reported so far for ammonium [43,44], imidazolium [45][46][47][48], pyridinium-based ILC [49], or miscellaneous type of ILC [50][51][52][53][54]. Generally, as the smectic phases are the most common phases for ILCs, especially due to electrostatic interactions, the nematic phase can be seen rather as an exception.…”