Proton behavior within the hydrogen bond (HB) networks of five molecular complexes of the proton sponge DMAN and different organic acids is investigated by single crystal neutron diffraction. The complexes form with either 2:1 (acid:DMAN) or 1:1 stoichiometric ratios and contain common structural motifs. All show proton transfer from an acid to DMAN forming a DMANH + moiety and hydrogen bonded acid dimers; complexes with halobenzoic acids have acid molecules linked by short, strong, charge-assisted HBs, while all complexes contain a short, strong, intramolecular N-H•••N HB in DMANH +. The hydrogen atom behavior within the short, strong HBs, accurately described from the neutron data, is rationalized in terms of weak interactions in the local crystal environment, with the position of the proton within both sets of short, strong HBs affected by a combination of the weak interactions in the vicinity of the HBs. A correlation is also found between the thermal motion of the bound proton in the N-H•••N HB of DMANH + and nearby oxygen atoms when they are sufficiently close to one another. This work shows that all interactions in the local environment combine to determine the behavior of protons within short, strong HBs and that by taking these interactions into account further control over the crystal structure and properties may be achievable.

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The hydrolysis of the chlorides and nitrates, etc., of calcium, magnesium, strontium and barium employed in the study of this problem, is so small that it alone cannot account for the results obtained. (3) Salts with water of crystallization increase the velocity of the saponification of an ester to a greater extent than salts with no water of crystallization. (4) On dilution, the effect with salts having water of crystallization decreases more rapidly than with salts without crystal water, which shows that the result cannot be due to hydrolysis alone. (5) The curves for the saponification of methyl formate are very similar to those for methyl acetate. (6) The large effect of salts with water of crystallization is probably due, in part, to their being hydrated, combined water being more highly ionized than free water. (7) The amount of the saponification, and, therefore, the position of the curve seems to be due to the combined effect of both cation and anion. (8) It is probable that anions as well as cations are somewhat hydrated. (9) The hydration of cations is inversely proportional to their atomic volumes. (IO) There seems to be a dilution of maximum saponification for each salt, (11) Hydrated salts show a large temperature coefficient, notwithstanding the decomposition of hydrates with rise in temperature, probably due in part to hydrolysis. (12) Decomposition of hydrates may play an important role in the increased velocity of chemical reactions with rise in temperature. (13) The chemical differences between free and combined water are analogous to the physical differences. Further work is riow in progress in this laboratory on this problem. Certain apparent discrepancies in this preliminary communication are being further investigated, and other lines of attack opened up. BALTIMORE. MD. [CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY OF THE JOHNS HOPKINS UNIVERSITY.

Developments in energetic materials are currently focused on the requirements for safer, yet still powerful materials for uses within mining, munitions and rocket propulsion systems One strategy that can be used to achieve these desirable properties is to synthesise new molecules, but this is both time-consuming and resource-intensive. Instead, another strategy is to crystallise energetic molecules with other molecules to form salts or cocrystals. This approach has been used extensively within the pharmaceutical industry in order to enhance desirable properties, e.g. solubility and bioavailability. To date, however, there has been very little research on the cocrystallisation of energetic materials. Examples include trinitrotoluene (TNT) with pyrene, naphthalene, and CL-20. To start this design process, the relationships between the types and strengths of interactions within a crystal structure and materials properties need to be established. Once these structure-property relationships have been established, the engineering of new and improved energetic materials can be achieved. The main focus of this work is on the energetic material 3-nitro-1,2,4-triazol-5-one (NTO) and the characterisation of a selection of new salts and cocrystals. NTO is an insensitive high explosive that has a similar performance to the more widely used explosive, RDX, yet is more stable, less prone to accidental detonation, and more soluble in water. Its high solubility in water is a major issue, as NTO is biologically active and represents a potential risk to the environment. There are only a few known salts of NTO and no published cocrystals, so the design and preparation of the first NTO cocrystals is a key objective. A selection of crystal structures of salts and cocrystals of NTO with nitrogen-rich aromatic systems has been obtained and the results are presented here. Interesting trends between pKa, functional groups, and intermolecular interactions have been observed.

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