The concept of buckminsterfullerene-like topology as a molecular-level structural motif has a long history in water cluster chemistry.[1] While carbon-based analogues have a well-established experimental foundation, "bucky-water" clusters remain largely conjectural species in the theoretical descriptions of pure water. Fullerene-like topologies are distinguished by the pattern of tricoordinate vertices in pentagonal and hexagonal facets that close to a convex polyhedron in three dimensions. They require exactly 12 pentagons and any number n hex of hexagons to form a polyhedron of 2n hex + 20 vertices. While pentagonal and hexagonal facets are well-known structural elements of all known crystalline forms of ice, [2] the intact Bucky-water polyhedra are principally recognized as elements in certain clathrate-type hydrates, such as the pentagonal dodecahedral (H 2 O) 20 (n hex = 0) and tetrakaidecahedral (H 2 O) 24 units (n hex = 2) of chlorine hydrate. [3] Today, gas hydrates are among the most well-known clathrate structures. These nonstoichiometric, crystalline compounds are found in natural-gas pipelines, on the ocean floor, and in permafrost environments, [4,5] deep ice cores, [6] rock inclusions, [7] comets, and certain outer planets. [8] There are three known types of natural-gas hydrates: the two cubic structures I and II, [9] and a hexagonal structure H.[ Recently, we extended a quantum statistical model of liquid water to include larger ice-like clusters, such as tetrahedral and fullerene-like clusters with up to 26 water molecules.[11] A low-energy tetrakaidecahedral (H 2 O) 24 cluster leads to a new low-temperature phase that bounds both liquid and vapor regions in first-order transition lines and gives rise to a true triple point. We characterized the microstructural composition and macroscopic properties of this "Bucky-ice" phase. Although it differs significantly from physical ice I h (for example, the melting point is 20 K too high and the molar volume is 5 % too low), it manifests qualitatively correct thermodynamic features of true ice polymorphs, which suggests an important role of voluminous clusters in the liquid/solid transition region. Thus understanding the structure and stability of such water clusters is of crucial importance for studying clathrate hydrates and hydration phenomena.The aim of this work is to investigate properties of larger water clusters including up to 60 water molecules. Some key questions will be addressed: Which of the calculated water clusters present minimum structures? How important are cooperative effects with increasing cluster size? Can hydrophobic guest molecules promote structure formation? Are larger clathrate structures than those known experimentally reasonable based on energetic considerations?The calculated bucky-water clusters having between 20 and 60 water molecules are shown in Figure 1. The variety of water cage structures comprises the dodecahedral (H 2 O) 20 cluster (n hex = 0), the tetrakaidecahedral (H 2 O) 24 cluster (n hex = 2), the hexakaidecahed...

The interest in ionic liquids (ILs) is steadily increasing because of their fascinating physicochemical properties and because of their broad range of applications in synthesis, separation, catalysis and electrochemistry. However, the multiplicity of their uses strongly depends on a molecular understanding of their exceptional properties. One key to a better understanding of their unique properties are spectroscopic studies of ionic liquids in conventional organic solvents in combination with DFT calculations and molecular dynamics simulations. Therefore we investigated the mixtures of the imidazolium-based ionic liquid [C(2)mim][NTf(2)] with methanol. Caused by the amphiphilic character of methanol both liquids are miscible over the whole mixture range. The scope of this work is to study the changes in the IL network upon dilution and to investigate the formation of methanol clusters embedded in the IL matrix. The mixtures were studied by FTIR spectroscopy in the mid-infrared region. The formation of methanol clusters was studied from the OD stretching vibrational bands between 2300 and 2800 cm(-1). The cluster populations of methanol could be derived from molecular dynamics simulations for the same mixtures. Weighting the DFT calculated frequencies by the cluster populations we could reproduce the measured spectra in the OD stretching region up to X(MeOH)=0.5. Above X(MeOH)=0.8, strong formation of self-methanol clusters takes place resulting in increasing diffusion coefficients related to decreasing dynamical heterogeneities. Thus we obtained a deep understanding of the solute-solvent and solute-solute interactions as well as information about the presence of microheterogeneities in the mixtures.

Fast-field-cycling relaxometry is a nuclear magnetic resonance method growing in popularity; yet, theoretical interpretation is limited to analytical models of uncertain accuracy. We present the first study calculating fast-field-cycling dipolar coupling directly from a molecular dynamics simulation trajectory. In principle, the frequency-resolved dispersion contains both rotational and translational diffusion information, among others. The present joint experimental/molecular dynamics study demonstrates that nuclear magnetic resonance properties calculated from the latter reproduce measured dispersion curves and temperature trends faithfully. Furthermore, molecular dynamics simulations can verify interpretation model assumptions by providing actual diffusion coefficients and correlation times.

The heterogeneity in dynamics has important consequences for understanding the viscosity, diffusion, ionic mobility, and the rates of chemical reactions in technology relevant systems such as polymers, metallic glasses, aqueous solutions, and inorganic materials. Herein, we study the spatial and dynamic heterogeneities in ionic liquids by means of solid state NMR spectroscopy. In the H spectra of the protic ionic liquid [TEA][OTf] we observe anisotropic and isotropic signals at the same time. The spectra measured below the melting temperature at 306 K could be simulated by a superposition of the solid and liquid line shapes, which provided the transition enthalpies between the rigid and mobile fractions. Consequently, we measured the spin-lattice relaxation times T for the anisotropic and the isotropic signals for the temperature range between 203 and 436 K. Both dispersion curves could be fitted to models including rotational correlation times, activation barriers and rate constants. This approach allowed determining the rotational correlation times for the N-D molecular vector of the [TEA] cation in differently mobile environments. The mobility is only slightly different, as indicated by small differences in activation energies for these processes. The NMR correlation times for the highly mobile phase are linearly related to measured viscosities, which supports the applicability of the Stokes-Einstein-Debye relation.

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