J. Phys. Chem. Lett.

Hydrogen bonds play a key role in the properties of materials. Herein, we report the geometry, strength, and distribution of three types of H-bonds formed in a mixture of an ionic and a molecular liquid. Such a variety of intermolecular interactions may provide solvents with potential application in H-bond-related chemistry.

J. Phys. Chem. Lett. 14, 10, 2684–2691, 2023

J. Phys. Chem. Lett.

The delicate balance of hydrogen bonds between ions of like charge and ions of opposite charge governs the properties of ionic liquids. Herein, we report that cationic cluster formation does not only change the local structures, but also influences the dynamics of the cations in a characteristic way.

J. Phys. Chem. Lett.  14, 17, 4019–4025, 2023



Tunneling driven dynamics for the PD3 group of the octyl phosphonium cation in an ionic liquid has been observed by means of solid-state NMR spectroscopy. Deuteron line-shape analysis and relaxation time measurements provide information about the structure, mobility and rearrangements of the cations in the solid, supercooled and liquid states. Hydrogen bonds of different strengths allow the change in molecular ordering upon phase transformation to be mapped. More information can be found in the Research Article by D. I. Kolokolov, R. Ludwig et al. (Cover Feature)

Chemistry, 28(23), 2022


The Front Cover illustrates the isotope effects for the protic ionic liquid (PIL) triethylammonium methanesulfonate as explored by deuterium solid-state NMR spectroscopy. The 2H NMR line shape analysis provides deuteron quadrupole coupling constants, which are sensitive for hydrogen bonding and allow probing the characteristics of a broad heterogeneous phase. More information can be found in the Research Article by Daniil I. Kolokolov, Ralf Ludwig and co-workers. (Front Cover)

ChemPhysChem, 23, 23, 2022



The Front Cover shows one of the three types of hydrogen bonding observed in hydroxy-functionalized halide salts. Here, the halide anion forms a hydrogen bond to the hydroxy group and interacts with the ring system of the cation at the same time. The versatility of structures demonstrates the importance of non-covalent interactions, in particular the role of hydrogen bonding. (Front Cover)

ChemPhysChem, 22, 1850-1856, 2021

Chem. Methods

The Cover Feature shows that the spectroelectrochemical methods simultaneously record spectral and electrochemical data that often contain more chemical information than can be conveniently analysed. In this work, we present a method for the extraction of individual chemical signatures from single-run spectroelectrochemical measurements. In combination with computational chemistry, this new approach will likely be helpful to better understand the electrochemistry of a wide range of molecular complexes. The cover was designed by J. J. Wending. More information can be found in the full paper by Benedict J. Elvers et al. (Cover Feature)

Chem. Methods, 1, 22-35, 2021



This work nicely shows that attractive local and directional interactions such as hydrogen bonds are able to overcome repulsive long-range and undirected interactions. In the future, we want to show that by forming clusters of ions with like charge, we can control the properties of ionic liquids, such as viscosity, conductivity or phase behavior. (Front Cover)

ChemPhysChem, 2020, Band 21, Ausgabe 21


Angewandte Chemie

The secrets of ionic liquids' properties rely on the delicate balance between Caoulomb interaction, hydrogen bonding and dispersion forces. In their Communication on page 8589 ff. S. P. Verevkin, R. Ludwig et al. show how these different types of interactions contribute to vaporization enthalpies. For the detailed analysis, exclusively experimental methods and a well-suited set of ionic and molecular liquids were used. (Inside Back Cover)

Angew. Chem. Int. Ed., 2019, Band 58, Ausgabe 25

Physical Chemistry Chemical Physics

This paper reports quantum chemical calculations of the kinetic and thermodynamic stability of cationic dimers. With increasing akly chain lenght, cooperative hydrogen bonds overcome the repulsive Coulomb forces. The cationic dimers with longer alkyl chains should be observable in gas phase experiments at low temperatures. (Back Cover)

Phys. Chem. Chem. Phys., 2019, Band 21, Ausgabe 16


Chemistry a European Journal

Understanding the mechanism of photocatalytic water reduction is essential for the development of effective catalysts. A new, self‐assembling, and sulfur‐free [FeFe]‐hydrogenase mimic, which shows good catalytic activity, is described. The action of the visible‐light‐driven iron catalyst within the cycle of H2 production from water is monitored by a combination of in‐situ spectroscopic methods. More information can be found in the Full Paper by R. Ludwig et al.



The Cover Feature visualizes how hydrogen bonding can overcome Coulomb repulsion in clusters of like‐charged ions. In their communication Ludwig et al. report kinetically stable cationic clusters with a high net charge up to Q=+6e. Despite strongly repulsive Coulomb forces, the hydroxy‐functionalized N‐(3‐hydroxypropyl)pyridinium cations are trapped by hydrogen bonding in a cyclic hexamer. (Cover Feature)

ChemPhysChem, 2018, Band 19, Ausgabe 14

Chemical Communications

We show that solid state NMR spectroscopy is a suitable method to study spatial and dynamic heterogeneities in ionic liquids. The deuteron spectra provide anisotropic and isotropic signals, which are related to distinct dynamical states in this unique liquid material. (Inside Back Cover)

Chem. Commun., 2018, Ausgabe 25


Angewandte Chemie

Hydrogen bonds between ions are identified by the first deuteron quadrupole coupling constants (DQCCs) for protic ionic liquids (PILs), measured by solid-state NMR spectroscopy. In their Communication (DOI: 10.1002/anie.201708340) D. I. Kolokolov R. Ludwig, et al. show that this NMR parameter is a sensitive probe of the doubly ionic hydrogen bonds present in PILs. The picture shows the NMR spectra as bridges symbolizing the doubly ionic hydrogen bonds between oppositely charged ions in PILs and mimicking the rocky mountains in the background.(Innentitelbild)

Angew. Chem., 2017, Band 129, Ausgabe 45

Chemical Communications

The protonation equilibrium of N-methyl-6-oxyquinolone can be used as a molecular pH meter in molecular solvents and even in ionic liquids. We show that a combination of optical spectroscopy and a mathematical algorithm provides the number of acidic protons.(Rücktitelbild)

Chem. Commun., 2017, Band 53, Ausgabe 78

Physical Chemistry Chemical Physics

This paper reports the calculation of the kinetic and thermodynamic stability of cation clusters with added molecules or counterions. These clusters of like-charged ions are stabilized by cooperative hydrogen bonding between hydroxyl groups overcoming the repulsive Coulomb forces. The cationic clusters show characteristic spectroscopic properties and some of them should be observable in demanding gas phase experiments. (Rücktitelbild)

Phys. Chem. Chem. Phys. , 2017, Band 19, Ausgabe 29

Chemie konkret

Das Foto zeigt ein oktaedrisches THF-Clathrat-Hydrat mit Schulter. Im Beitrag auf S. 59 wird gezeigt, wie sich solche THF-Clathrat-Hydrate mit einfachen Mitteln in einer Unterrichtsstunde herstellen lassen. Methanhydrate können als potentielle fossile Energielieferanten im Unterricht thematisiert werden und Einblicke in ein aktuelles und nicht abgeschlossenes Forschungsthema geben.(Titelbild)

CHEMKON, 2017, Band 24, Ausgabe 2

Physical Chemistry Chemical Physics

This article reports the temperature dependence of the solvation behaviour of light gases in ionic liquids. Extensive molecular dynamics simulations show that the solubility of gases ranging from molecular hydrogen to carbon dioxide is determined by entropy–enthalpy compensation. Our model can provide reliable estimates for the solvation behaviour, where conflicting or no experimental data exist.(Innentitelbild)

Phys. Chem. Chem. Phys.,2017, Band 19, Ausgabe 3


Physical Chemistry Chemical Physics

Ludwig et al. describe a method for the accurate determination of deuteron quadrupole coupling constants and reorientational correlation times in protic ionic liquids by means of NMR relaxations time experiments, DFT-calculations and molecular dynamics simulations. (Titelbild)

Phys. Chem. Chem. Phys., 2016, Band 18, Ausgabe 27


Cyclic tetramer of hydrogen-bonded cations in the 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ionic liquid. Weinhold, Ludwig et al. could assign the observed vibrational modes in the infrared spectra to DFT-calculated frequencies of clusters of like-charged ions. More information can be found in the Cummunication by F. Weinhold, R. Ludwig et al. on page 458 in Issue 4, 2016 (Titelbild)

ChemPhysChem, 2016, Band 17, Ausgabe 4


Physical Chemistry Chemical Physics

This communication reports the ‘jumping and pecking’ motion of the cholinium cation in ionic liquids. The counterintuitive phenomenon of like-charge attraction is observed by infrared spectroscopy and supported by DFT calculations. The cation–cation hydrogen bond is as strong as that in the ethanol dimer. Although not thermodynamically favoured, the like-charge clusters are stabilized kinetically. This information is useful to understand the competition between like-charge repulsion and hydrogen bond attraction and its infl uence on transport properties. (Rücktitelbild)

Phys. Chem. Chem. Phys., 2015, Band 17, Ausgabe 46


Hydrogen bonding governs the vibrational dephasing in ionic liquids. Time-resolved coherent anti-Stokes Raman scattering (CARS) and theoretical studies show that this process takes place on the fs-to-ps timescale. More information can be found in the Full Paper by R. Ludwig, S. Lochbrunner, O. Kühn et al. on p. 2519. (Rücktitelbild)

ChemPhysChem, 2015, Band 16, Ausgabe 12



Physical Chemistry Chemical Physics

This communication reports the competition between hydrogen bonding and dispersion interaction in protic ionic liquids. It is shown that dispersion forces can be as strong as hydrogen bonds and that they influence vibrational frequencies in the far infrared to different extents. This information is useful to understand the subtle balance between Coulomb interaction, hydrogen bonding and dispersion forces and the effect on the properties of these Coulomb dominated systems. (Rücktitelbild)

Phys. Chem. Chem. Phys., 2015, Band 17, Ausgabe 21

Angewandte Chemie

The secrets of ionic liquid properties rely on the subtle energy balance between Coulomb interaction, hydrogen bonding, and dispersion forces. In their Communication, R. Ludwig et al. show that far-infrared spectroscopy is suitable to study the competition between hydrogen bonding and dispersion interactions in these Coulomb-dominated liquids. Characteristic spectral signatures allow the transition between both types of noncovalently bound “ion pairs” to be quantified. (Innentitelbild)

Angew. Chem., 2015, Band 54, Ausgabe 9


Physical Chemistry Chemical Physics

Low vibrational spectroscopy provides detailed information on the strength and type of interaction and their influence on the properties of ionic liquids.(Titelbild)

Phys. Chem. Chem. Phys., 2014, Band 16, Ausgabe 40

ACS Catalysis

In situ spectroscopic investigations on homogeneous iridium catalysts for the hydroformylation of olefins. HP-FTIR and NMR spectroscopy have been applied for the characterization and quantification of an equilibrium mixture of iridium hydrido complexes.  Spectroscopic data were analyzed by chemometric methods, and FTIR spectra have been compared with calculated spectra obtained by DFT methods.(Titelbild)

ACS Catal., 2014, Band 4, Ausgabe 7

Chemistry A European Journal

Happy birthday, ethylammonium nitrate! The first widely known ionic liquid, studied by Paul Walden, turns 100 years old. Some important properties of EAN have been addressed properly for the first time. In their Communication on page 11640 ff., R. Ludwig, S. Verevkin et al. show that ethylammonium nitrate evaporates as contact-ion pairs at low temperatures (<419 K). Above that temperature, neutral molecules dominate over ion pairs, resulting in the relatively low boiling point of 513 K.(Innentitelbild)

Chem. Eur. J., 2014, Band 20, Ausgabe 37



On p. 3102 ff., Ludwig et al. report infrared measurements on trace amounts of water dissolved in ionic liquids. Using water as a sensitive probe they show that ionic liquids can be more hydrophobic than molecular liquids. This is a surprising result, given that the liquid material consists solely of ions. (Innentitelbild)

ChemPhysChem, 2012, Band 13, Ausgabe 13


Angewandte Chemie

Um zu verstehen, wie die photokatalytische Wasserspaltung abläuft, ist für die rationale Entwicklung effektiver Katalysatoren essenziell. In ihrer Zuschrift nutzten R. Ludwig, M. Beller, A. Brückner et al. eine Kombination aus drei pektroskopischen In-situ-Methoden, um das Zusammenspiel von Iridium- und Eisenkatalysatoren im Zyklus der H2-Produktion aus Wasser zu verfolgen, und konnten so den Reaktionsmechanismus bestätigen. (Rücktitelbild)

Angew. Chem., 2011, Volume 123, Issue 43



The determination of enthalpies of vaporization for ionic liquids is a real challenge. R. Ludwig et al. show on p. 1623 that this important thermodynamic property can be estimated from low vibrational bands in the far infrared spectra of this new liquid material. (Innentitelbild)

ChemPhysChem, 2010, Band 11, Ausgabe 8


The rhodium-catalyzed hydroformylation of 3,3-dimethyl-1-butene is monitored by in situ, high-pressure FTIR spectroscopy, as pictured, giving time-dependent concentration profiles of organic components and metal-organic reaction intermediates. In their paper on page 287 ff., Selent et al. offer an improved perception of mono- and diphosphite-modified catalysis. (Innentitelbild)

ChemCatChem, 2010, Band 2, Ausgabe 3

Angewandte Chemie

Die Bedeutung von Wasserstoffbrücken in ionischen Flüssigkeiten (ILs) war bislang umstritten. In ihrer Zuschrift auf S. 459 ff. zeigen R. Ludwig et al. nun, dass die Wechselwirkung zwischen Anionen und Kationen durch lokale und gerichtete Wasserstoffbrücken verstärkt werden kann. Ferninfrarotspektren ausgesuchter ILs lassen darauf schließen, dass die Frequenzverschiebungen der intermolekularen Streckschwingungen auf unterschiedlichen Möglichkeiten zur H-Brückenbildung beruhen. (Innentitelbild)

Angew. Chem., 2010, Band 122, Ausgabe 2



The cover picture shows water molecules in different hydration shells at the surface of the model protein ubiquitin. The properties of proteins and the role of solvent in conformational dynamics is a central topic to the DFG-Foschergruppe (FOR 436) which forms the basis of this special issue. The polymorphism, dynamics and function of water at molecular interfaces is discussed with contributions from R. Winter (p. 2715, 2779), Ludwig (p. 2722, 2731), Geiger and Paschek (p. 2722, 2737, 2742), Brovchenko (p. 2660, 2695), Tolan (p. 2809), Marx (p. 2703, 2751, 2759), and Weingärtner (p. 2794, 2802). (Titelbild)

ChemPhysChem, 2008, Band 9, Ausgabe 18



The cover picture shows a snapshot from a molecular dynamics (MD) simulation of the nanostructured ionic liquid [C2mim][NTf2]. In their article on page 2464 Köddermann et al. have developed an atomic-detail molecular force field for ionic liquids of type [Cnmim][NTf2] (n=2,4,6,8). This is the first time such a model is capable of correctly describing structural, dynamical and thermodynamical properties of these ionic liquids over a wide temperature range.. (Titelbild)

ChemPhysChem, 2007, Band 8, Ausgabe 17