Spectroscopic Evidence for Clusters of Like‐Charged Ions in Ionic Liquids Stabilized by Cooperative Hydrogen Bonding

Knorr, Anne; Stange, Peter; Fumino, Koichi; Weinhold, Frank; Ludwig, Ralf

doi:10.1002/cphc.201501134

Cited by 117 publications

(118 citation statements)

References 42 publications

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“…doubly-ionic B + ⋯H-A + or B -⋯H-Abinding between ions of like charge. cyclic tetramers [98]. But despite such strong electrostatic opposition, AEHB species are found to achieve robust kinetic stability upon reaching typical H-bond distance to form a distinctive attractive well with significant dissociation barrier (e.g.…”

Section: Mutually Consistent Correlations For Characterising H-bondingmentioning

confidence: 99%

What is NBO analysis and how is it useful?

Weinhold

Landis

Glendening

2016

International Reviews in Physical Chemistry

671

391

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Natural bond orbital (NBO) analysis is one of many available options for 'translating' computational solutions of Schrödinger's wave equation into the familiar language of chemical bonding concepts. In this Review, we first address the title questions by describing characteristic features that distinguish NBO from alternative analysis methodologies (e.g. of QTAIM or EDA type) and answering criticisms that have been raised in specific chemical applications. We then address the general 'usefulness' of NBO analysis in the context of widely accepted philosophical criteria, including (i) broad consistency, both internally and with respect to known experimental data, (ii) multi-faceted predictive capacity, including numerical model predictions of specific properties, general correlative and statistical regression relationships, and 'risky' falsifiable predictions of previously unknown chemical phenomena, and (iii) general pedagogical value, promoting organisation, unification, and orderly rationalisation of chemical knowledge. Specific chemical topics chosen for discussion include controversial H⋯H 'bond lines' in bay-type hydrocarbon species; carbene ligation of coinage metals; resonance-type bonding of noble gas hydrides; NBO descriptors in Hammett-type quantitative structure-activity relationships; nature of conventional and 'anti-electrostatic' hydrogen bonding interactions; multi-centre bonding in 'aromatic' Al ð2ÀÞ 4 , Lewis-like hybridisation picture of non-VSEPR geometry and high-order multiple bonding in transition metal species; resonance origin of the '18e rule'; and localised (symmetry-independent) prediction of Jahn-Teller effects in free radical chemistry. We conclude with hints of some directions for future extensions of NBO methods.

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Section: Mutually Consistent Correlations For Characterising H-bondingmentioning

confidence: 99%

What is NBO analysis and how is it useful?

Weinhold

Landis

Glendening

2016

International Reviews in Physical Chemistry

671

391

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“…[27] They are supported by the layered structure (see Figure 2) and the stacking clearly compensates for the anionic repulsive forces.T he situation is similar to that in ILs in which H-bonds can overcome the repulsion between like-charged ions. [28][29][30][31][32][33] TheX -ray structural features are strongly supported by B3LYP/6-311G** and B3LYP-D3/6-311G** calculations on dimers and tetramers of ion-pairs. [34][35][36] Cut-outs of the X-ray structures are used as starting geometry.Only if the dispersion correction is taken into account do the optimized structures resemble the X-ray structures,which are mainly characterized by the stacking between the rings of N-methyl-6-hydroxyquinolinium cations and the hydrogen bond between the hydroxy proton and the sulfonyl oxygen atom (see SI7).…”

Section: Introductionmentioning

confidence: 95%

Large Stokes Shift Ionic‐Liquid Dye

et al. 2017

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Abstract:We have incorporated the dye N-methyl-6-oxyquinolone [6MQz] in its protonated form as acation into an ionic liquid (IL) and thus to synthesize an IL dye.T he IL dye N-methyl-6-hydroxyquinolinium bis(trifluoromethylsulfonyl) imide [6MQc][NTf 2 ]w as characterized by NMR, ATRI R spectroscopya nd X-ray crystallography.T he fluorescence of the IL dye has al arge Stokes shift of Dl = 116 nm and aq uantum yield of f F = 0.56 in acetonitrile.C haracteristic solvent dependent shifts can be detected in the emission spectra. In other ILs,acetonitrile and THF we observe abathochromic shift of up to 28 nm compared to the pure IL dye at 467 nm. Forstronger polar solvents the fluorescence signals are strongly red-shifted to 650 nm indicating proton transfer to the solvent molecules in the excited state.T his underlines the importance of the IL building block [ MQc] + as photo acid.Fluorescent dyes are important tools in many branches of chemistry related sciences,s uch as biological chemistry, [1][2][3][4][5][6][7][8] materials science, [9][10][11] or solar-energy conversion. [12,13] Attractive fluorescent dyes are characterized by their extended spectral range,h igh emission quantum yields,p hotostability and good solubility in the solvent. Thef luorescent dye N-methyl-6-oxyquinolone [6MQz] was used for studying solvation phenomena. Thec olor of this solvatochromatic dye molecule depends strongly on the polarity of the surrounding,a st he permanent dipole moments strongly change upon excitation from the ground to the excited state.T hus [6MQz] has been used as dye for understanding solvation processes and proton transfer to solvents. [14][15][16][17][18][19][20][21][22] In some cases the polarity probe was incorporated into biomolecules such as sugars or enzymes for probing the chemical environment and providing biocompatibility. [10,11,18,19] Whereas other dyes have been extensively applied to probe the polarity of ionic liquids,t he protonated form of [6MQz] has never been used as moiety of an ionic liquid itself. [23,24] Thus,t he goal of our work was to incorporate the dye N-methyl-6-oxyquinolone [6MQz] in its protonated form as acation into an ionic liquid (IL) and thus to synthesize an IL dye.T he resulting ionic liquid dye N-methyl-6-hydroxyquinolinium bis(trifluoromethylsulfonyl) imide ]involves anion metathesis reaction and is shown in Scheme 1. Initial N-methyl-6-hydroxyquinolinium iodide was prepared using ak nown procedure which is also described in the Supporting Information (SI0). [25,26] Then, equimolar amounts of N-methyl-6-hydroxyquinolinium iodide (287 mg, 1mmol) and silver bis(trifluoromethylsulfonyl)imide (388 mg, 1mmol) were dissolved in 15 mL water each. Thet wo solutions were combined and the reaction mixture was stirred for 15 min. Silver iodide,which precipitates instantly,was filtered off and discarded. Them other liquor was removed on ar otary evaporator and the residue was dissolved in 25 mL ethanol to carry out ah ot-filtration with activated charcoal. After filtration, the solvent wa...

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“…In Figure 7, we observe no discontinuous jump in frequency for the mixture after five washes. It is known that the hydrogen bond cooperativity due to concerted charge transfer can greatly enhance the strength of the individual hydrogen bonds involved in the coupling [25]. Hydrogen-bonding non-additivity and the size of clusters are suggested to be responsible for the enhancement of hydrogen bonding [25,26].…”

Section: Resultsmentioning

confidence: 99%

“…It is known that the hydrogen bond cooperativity due to concerted charge transfer can greatly enhance the strength of the individual hydrogen bonds involved in the coupling [25]. Hydrogen-bonding non-additivity and the size of clusters are suggested to be responsible for the enhancement of hydrogen bonding [25,26]. Thus, the anomalous jump in frequency at 0.4 GPa can be attributed to both the cooperative and geometric effects of blue-shifting hydrogen bonds.…”

Section: Resultsmentioning

confidence: 99%