Water is of fundamental importance for human life and plays an important role in many biological and chemical systems. Although water is the most abundant compound on earth, it is definitely not a simple liquid. It possesses strongly polar hydrogen bonds which are responsible for a striking set of anomalous physical and chemical properties. For more than a century the combined importance and peculiarity of water inspired scientists to construct conceptual models, which in themselves reproduce the observed behavior of the liquid. The exploration of structural and binding properties of small water complexes provides a key for understanding bulk water in its liquid and solid phase and for understanding solvation phenomena. Modern ab initio quantum chemistry methods and high-resolution spectroscopy methods have been extremely successful in describing such structures. Cluster models for liquid water try to mimic the transition from these clusters to bulk water. The important question is: What cluster properties are required to describe liquid-phase behavior?

Hydrogen bonds are very important in chemistry and biology. [1][2][3] The properties of liquids and solutions consisting purely of neutral molecules are characteristically determined by the strength and number of hydrogen bonds. When water freezes to form ice, each water molecule forms four strong hydrogen bonds to its neighbors in tetrahedral fashion giving a periodical H-bond network.[4] In nonpolar solvents peptides retain their helical secondary structure up to very high temperature as a result of intramolecular H bonds.[5] Nucleic acids when neutralized in aqueous electrolyte solutions build the famous double-helical structure on the basis of strong two-and threefold hydrogen bonds between base pairs. [6] What all these important structures have in common is that they are stabilized by hydrogen bonds; they usually become more rigid and less flexible with increasing strength and number of H bonds.In this study we show that the opposite behavior can be found for ionic liquids (ILs), which are composed solely of ions rather than neutral molecules. ILs constitute a remarkably promising class of technologically useful and fundamentally interesting materials. [7][8][9][10][11][12] Herein we show that strong and directional H bonds formed between cations and anions destroy the charge symmetry and thus can fluidize ionic liquids. H bonds introduce "defects" into the Coulomb network of ILs and increase the dynamics of the cations and anions, resulting in decreased melting points and reduced viscosities. Thus the properties of ILs can be altered by adjusting the ratio between Coulomb forces and van der Waals interactions represented by H bonds. This possibility is demonstrated by FTIR measurements of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C 2 mim]-[NTf 2 ] (1) and 1-ethyl-2,3-dimethylimidazolium bis(trifluoro methylsulfonyl)imide [C 2 C 1 mim][NTf 2 ] (2), wherein characteristic H-bond contributions can be switched off by methylation at C(2).Recently, we presented low-frequency vibrational spectra of imidazolium-based ionic liquids in the range between 30 and 300 cm À1 obtained by far-infrared spectroscopy.[13] We could show that the absorptions at wavenumbers above 150 cm À1 can be assigned to intramolecular bending and wagging modes of cations and anions in the ionic liquid. The contributions below 150 cm À1 were assigned to the intermolecular interactions between cations and anions that describe the bending and stretching vibrational modes of hydrogen bonds. This assignment was supported by DFT calculations which gave wavenumbers for the bending and stretching modes of ion pairs and ion-pair aggregates in this frequency region. Further proof of the intermolecular interactions came from a nearly linear relation between the average binding energies of calculated IL aggregates and the measured wavenumbers for maxima of the low-frequency vibrational bands for a series of ionic liquids containing the same imidazolium cation but different anions. Although this assignment is supported by recent THz...

Hydrogen is one of the essential reactants in the chemical industry, though its generation from renewable sources and storage in a safe and reversible manner remain challenging. Formic acid (HCO(2)H or FA) is a promising source and storage material in this respect. Here, we present a highly active iron catalyst system for the liberation of H(2) from FA. Applying 0.005 mole percent of Fe(BF(4))(2)·6H(2)O and tris[(2-diphenylphosphino)ethyl]phosphine [P(CH(2)CH(2)PPh(2))(3), PP(3)] to a solution of FA in environmentally benign propylene carbonate, with no further additives or base, affords turnover frequencies up to 9425 per hour and a turnover number of more than 92,000 at 80°C. We used in situ nuclear magnetic resonance spectroscopy, kinetic studies, and density functional theory calculations to explain possible reaction mechanisms.

The parameterization of a new force-field and its validation for the liquid description of five imidazolium-based ionic liquids [C(n)mim][NTf2] (n=1,2,4,6,8) are described. The proposed force-field is derived to reproduce densities, self-diffusion coefficients for cations and ions as well as NMR rotational correlation times for cations and water molecules in [C(2)mim][NTf2]. The temperature dependence and the cation chain-length dependence of these properties is described well. Very good agreement between simulated and experimental values for the heats of vaporization, shear viscosities and NMR rotational correlation times is also achieved. All properties are crucial for understanding the nature and interaction of ionic liquids. The good performance of the new force-field suggests that the Lennard-Jones interactions previously were strongly overestimated. The given force-field now allows us to investigate other important properties of this class of ionic liquids such as the micro segregation of ionic liquids, ion pair formation, lifetimes of ion pairs and the solvent dependency of these properties.