The program Mercury, developed by the Cambridge Crystallographic Data Centre, is designed primarily as a crystal structure visualization tool. A new module of functionality has been produced, called the Materials Module, which allows highly customizable searching of structural databases for intermolecular interaction motifs and packing patterns. This new module also includes the ability to perform packing similarity calculations between structures containing the same compound. In addition to the Materials Module, a range of further enhancements to Mercury has been added in this latest release, including void visualization and links to ConQuest, Mogul and IsoStar.

Mercury CSD 2.0 – new features for the visualization and investigation of crystal structures

The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in the composition of moving water and by the effects of particulate suspended material. Some constituents are unstable and require onsite determination or sample preservation. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents

Study and Interpretation of the Chemical Characteristics of Natural Water

From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids.

The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

The hydrogen bond in the solid state.

Carbon dioxide in water and seawater: the solubility of a non-ideal gas

Whereas much of organic chemistry has classically dealt with the preparation and study of the properties of individual molecules, an increasingly significant portion of the activity in chemical research involves understanding and utilizing the nature of the interactions between molecules. Two representative areas of this evolution are supramolecular chemistry and molecular recognition. The interactions between molecules are governed by intermolecular forces whose energetic and geometric properties are much less well understood than those of classical chemical bonds between atoms. Among the strongest of these interactions, however, are hydrogen bonds, whose directional properties are better understood on the local level (that is, for a single hydrogen bond) than many other types of non-bonded interactions. Nevertheless, the means by which to characterize, understand, and predict the consequences of many hydrogen bonds among molecules, and the resulting formation of molecular aggregates (on the microscopic scale) or crystals (on the macroscopic scale) has remained largely enigmatic. One of the most promising systematic approaches to resolving this enigma was initially developed by the late M. C. Etter, who applied graph theory to recognize, and then utilize, patterns of hydrogen bonding for the understanding and design of molecular crystals. In working with Etter's original ideas the power and potential utility of this approach on one hand, and on the other, the need to develop and extend the initial Etter formalism was generally recognized. It with that latter purpose that we originally undertook the present review.

Patterns in Hydrogen Bonding: Functionality and Graph Set Analysis in Crystals

The Ionization Constant of Carbonic Acid in Water and the Solubility of Carbon Dioxide in Water and Aqueous Salt Solutions from 0 to 50

Wahrend sich die klassische Organische Chemie bisher weitgehend mit der Synthese individueller Molekule und der Untersuchung ihrer Eigenschaften beschaftigte, gewinnen nunmehr zunehmend Forschungsaktivitaten an Bedeutung, die sich mit dem Verstandnis und dem Ausnutzen von Wechselwirkungen zwischen Molekulen befassen. Zwei fur diese Entwicklung reprasentative Gebiete sind die supramolekulare Chemie und die molekulare Erkennung. Die Wechselwirkungen zwischen Molekulen werden durch intermolekulare Krafte bestimmt, deren energetische und geometrische Eigenschaften viel weniger gut verstanden sind als die von klassischen chemischen Bindungen zwischen Atomen. Zu den starksten dieser Wechselwirkungen gehoren die H-Brucken, deren gerichtete Eigenschaften auf lokalem Niveau (d. h. fur nur eine H-Brucke) besser als die vieler anderer Typen nichtbindender Wechselwirkungen verstanden werden. Trotzdem ist noch weithin ungeklart, wie man vorgehen muste, um die Konsequenzen der Bildung vieler H-Brucken zwischen Molekulen und den daraus folgenden Aufbau von molekularen Aggregaten (im mikroskopischen Bereich) oder von Kristallen (im makroskopischen Bereich) zu charakterisieren, zu verstehen und vorherzusagen. Einer der vielversprechendsten systematischen Ansatze, um dieses Problem zu losen, wurde ursprunglich von der inzwischen verstorbenen M. C. Etter entwickelt. In den letzten Jahren wurden ihre Ideen von anderen ubernommen und angewendet. Diese Arbeiten bewiesen einerseits die Bedeutung und die potentielle Nutzlichkeit der ursprunglichen Ideen und Ansatze, zeigten andererseits aber auch die Notwendigkeit auf, Etters Formalismus zu erweitern. Gerade letzteres war der Ausloser fur die hier vorgestellten Arbeiten.

Raymond E. Davis

Papers

Patterns in Hydrogen Bonding: Functionality and Graph Set Analysis in Crystals

The Ionization Constant of Carbonic Acid in Water and the Solubility of Carbon Dioxide in Water and Aqueous Salt Solutions from 0 to 50

Muster aus H‐Brücken: ihre Funktionalität und ihre graphentheoretische Analyse in Kristallen

Interpretation of the pseudocontact model for nuclear magnetic resonance shift reagents. I. Agreement factor, R

Interpretation of the pseudocontact model for nuclear magnetic resonance shift reagents. II. Significance testing on the agreement factor