Headgroups versus symmetry in congruent ion pairs: which one does the job in mesomorphic aryl guanidinium and aryl imidazolium sulphonates?

Butschies, Martin; Mansueto, Markus; Haenle, Johannes Christian; Schneck, Christof; Tussetschläger, Stefan; Gießelmann, Frank

doi:10.1080/02678292.2014.885600

Cited by 16 publications

(18 citation statements)

References 100 publications

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“…Cl with spacer lengths , C10 showed monotropic phase behaviour, forming small SmA phases upon first cooling (entries 5, 7). As recently reported, [35] bending of the cationic core by meta-substitution (m-3a . Cl) decreased melting and clearing points compared with the para-substituted analogue p-3a .…”

Section: Mesomorphic Properties Of Guanidinium Ilcsmentioning

confidence: 64%

“…[1][2][3][4][5] With high thermal stability, the ease of charge delocalization and coordination properties as well as the possibility to attach up to six different substituents on the guanidine moiety has driven research activities in diverse directions, resulting in their use as superbases, [6,7] ligands for coordination complexes, [8][9][10][11] organocatalysts, [12][13][14][15][16] stimuli-responsive materials, [17] hydrogels, [18] anion exchange polymer electrolytes for fuel cells, [19] and biologically active compounds [20][21][22][23][24][25][26][27][28][29] for drug development. Furthermore, guanidinium salts have also entered the field of ionic liquid crystals (ILCs) [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] as an alternative cationic head group to the imidazolium-derived ILCs, which have dominated this research area so far. …”

Section: Introductionmentioning

confidence: 99%

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Cyanobiphenyl versus Alkoxybiphenyl: Which Mesogenic Unit Governs the Mesomorphic Properties of Guanidinium Ionic Liquid Crystals?

et al. 2014

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A series of phenylguanidinium salts 3 . X, which are linked via an alkoxy spacer either to a 4-decyloxy-or 4-cyanosubstituted biphenyl mesogen, was prepared and the mesomorphism studied. A decyloxybiphenyl core and a spacer of at least C6 chain length were required for mesophase formation. Replacement of the chloride counterion by other anions like bromide or tetrafluoroborate improved the thermal stability of the mesophase. A comparison of substitution pattern (meta v. para) on the phenyl ring revealed decreased melting and clearing points for the bent cationic head group. All guanidinium ionic liquid crystals 3 displayed only smectic A (SmA) phases. A packing model is assumed where the molecules in a bilayer stack over each other in opposite direction with interdigitated terminal decyloxy groups and spacers.bromides 9 giving the tethered compounds p-10a,b and m-10b-e in 78-88 % yield. N-Boc-deprotection to derivatives p-11a,b and m-11b-e was achieved very cleanly with methane sulfonic acid in CHCl 3 . Derivative m-11a was obtained in 94 % yield by acidic hydrolysis [62] of acetamide m-7a. The aniline derivatives 11 were finally treated with chloro-N,N,N 0 ,N 0tetramethylformamidinium chloride [63] and either NEt 3 or NaHCO 3 . Workup strictly required an inert gas atmosphere to provide the neat target guanidinium salts 3 . Cl in 70-98 % yield. To further study the anion effect, decyloxybiphenyl guanidinium chloride m-3a . Cl was submitted to salt metathesis with NaBr, KI, NaOTf, NaBF 4 , KPF 6 , KOAc, and KSCN yielding the corresponding guanidinium ILCs m-3a . X (Scheme 2). Anion Effect in Guanidinium ILCsComparison of the 1 H NMR spectra of phenylguanidinium salts m-3a . X revealed a significant downfield shift of the N-H signal from ,7.5 to 12.0 ppm in the following order: PF 6 , BF 4 , OTf , I , SCN , Br ECl (Fig. 1).This correlation between the anion and the N-H proton shift indicates the presence of contact between the ion pairs that also led to small chemical shifts of the aromatic protons of the phenylguanidinium moiety (Fig. 1, grey). To estimate the effect of concentration on the N-H signal, 1 H NMR measurements of m-3b . Cl with concentrations varying from 0.83 to 2.50 mg mL À1 were carried out. The N-H signal shift of 0.1 ppm turned out to be negligible with respect to the strong dependence of the NH signal on the anion (see Supplementary Material for details). This effect rather might be due to either the interaction of the anion with the anisotropic cone of the aryl ring than due to the conjugation between the guanidinium cation and the aryl ring. Previous DFT calculations of several guanidinium salts revealed no or only very little conjugation, i.e. the guanidinium moiety behaves like an isolated cation. [39] In agreement with these studies, the N-H signal shifted upfield with increasing anion radii [64,65] with an almost linear correlation (Fig. 2).

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Section: Mesomorphic Properties Of Guanidinium Ilcsmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Cyanobiphenyl versus Alkoxybiphenyl: Which Mesogenic Unit Governs the Mesomorphic Properties of Guanidinium Ionic Liquid Crystals?

et al. 2014

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“…The counter ion provides an additional tool to efficiently modify the mesophase behavior of an ILC, but also other physical properties, including for instance viscosity [ 51 ]. To illustrate this, recent studies on the dimensional effects of anions (and cations) showed, in fact, that one should consider ILCs to be composed of “congruent ion pairs” rather than studying them independently [ 52 ]. Previous work did study the anion independently from the mesogenic cation, albeit the authors drew similar conclusions.…”

Section: Materials Development In Ionic Liquid Crystalsmentioning

confidence: 99%

Key Developments in Ionic Liquid Crystals

Fernandez

Kouwer²

2016

IJMS

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Ionic liquid crystals are materials that combine the classes of liquid crystals and ionic liquids. The first one is based on the multi-billion-dollar flat panel display industry, whilst the latter quickly developed in the past decades into a family of highly-tunable non-volatile solvents. The combination yields materials with a unique set of properties, but also with many challenges ahead. In this review, we provide an overview of the key concepts in ionic liquid crystals, particularly from a molecular perspective. What are the important molecular parameters that determine the phase behavior? How should they be introduced into the molecules? Finally, which other tools does one have to realize specific properties in the material?

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“…Hence, the influence of chain lengths, type of head group and counterion on the mesomorphic properties of ILCs has been investigated by several groups. [2][3][4]17,18] Furthermore, recent work by Tschierske, Cheng [19,20] and Laschat [21] has shown that by increasing the number of alkyloxy side chains on the same mesogenic unit the whole range of mesophase types from smectic A (SmA) to columnar (Col) and even cubic (Cub) could be obtained from structurally similar compounds. The effect of bending of the mesogenic core, however, has been explored much less, although it is well known from typical organic crystals (e.g.…”

Section: Introductionmentioning

confidence: 97%

Ionic liquid crystals derived from guanidinium salts: induction of columnar mesophases by bending of the cationic core

Antill¹,

Neidhardt²,

Kirres³

et al. 2014

Liquid Crystals

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2014) Ionic liquid crystals derived from guanidinium salts: induction of columnar mesophases by bending of the cationic core, Liquid Crystals, 41:7, 976-985, Meta-alkyloxyguanidinium salt-based ionic liquid crystals 3-5, 7 and 9 were synthesised and investigated with respect to the influence of meta-substitution of the cation on the mesomorphic properties. As expected, bending of the mesogenic cation in ion pairs with simple counterions (3-5) decreased melting points irrespective of the anion, but clearing points were influenced by the anion radii. SmA mesophases were formed in all cases. The mesophase formation in guanidinium sulphonates 7 and 9, however, depended not only on meta-substitution but also on the anion, the respective difference between alkyl chain lengths in cation and anion and the number of alkyloxy substituents on the sulphonate, for which a change of mesophase type from smectic to columnar phases was observed. For two derivatives, 7e and 9b, room temperature SmA and Col h mesophases could be obtained that were stable for a temperature range of 91 K and 55 K, respectively. A packing model for both smectic and columnar phases based on powder XRD data was proposed.

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Headgroups versus symmetry in congruent ion pairs: which one does the job in mesomorphic aryl guanidinium and aryl imidazolium sulphonates?

Cited by 16 publications

References 100 publications

Cyanobiphenyl versus Alkoxybiphenyl: Which Mesogenic Unit Governs the Mesomorphic Properties of Guanidinium Ionic Liquid Crystals?

Cyanobiphenyl versus Alkoxybiphenyl: Which Mesogenic Unit Governs the Mesomorphic Properties of Guanidinium Ionic Liquid Crystals?

Key Developments in Ionic Liquid Crystals

Ionic liquid crystals derived from guanidinium salts: induction of columnar mesophases by bending of the cationic core

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