PSSP, a computer program for the crystal structure solution of molecular materials from X-ray powder diffraction data

This work describes the computer program PSSP (powder structure solution program) for the crystal structure solution of molecular solids from X-ray powder diffraction data. This direct-space structure solution program uses the simulated annealing global optimization algorithm to minimize the difference between integrated intensities calculated from trial models and those extracted in a Le Bail fit of the experimental pattern, using a cost function for dealing with peak overlap through defined intensity correlation coefficients, computationally faster to calculate than R(wp). The methodology outlined is applicable to organic solids composed of moderately complex rigid and flexible molecules, using diffraction data up to relatively low resolution. PSSP performance tests using 11 molecular solids with six to 20 degrees of freedom are analyzed

Outstanding Advantages, Current Drawbacks, and Significant Recent Developments in Mechanochemistry: A Perspective View

Although known since antiquity, mechanochemistry has remained dormant for centuries. Nowadays, mechanochemistry is a flourishing research field at the simultaneous stages of gathering data and (often astonishing) observations, and scientific argumentation toward their analysis, for which the combination of interdisciplinary expertise is necessary. Mechanochemistry’s implementation as a synthetic method is constantly increasing, although it remains far from being fully exploited, or understood on the basis of fundamental principles. This review starts by describing many remarkable advantages of mechanochemical reactions, simplifying and “greening” chemistry in solutions. This description is followed by an overview of the current main weaknesses to be addressed in the near future toward the systematic study of its energetics and chemical mechanisms. This review finishes by describing recent breakthrough experimental advances, such as in situ kinetics monitoring using synchrotron X-ray powder diffraction and Raman spectroscopy, plus equally significant computational chemistry approaches, such as quantum mechanochemistry, used for the understanding of covalent or hydrogen bond ruptures in biomolecules or mechanophores in polymers at the single-molecule level. Combined with new technologies to control temperature and pressure in ball mills, these appealing new methods are promising tools for establishing the fundamental knowledge necessary for the understanding of mechanochemical reactivity and mechanisms

Outstanding Advantages, Current Drawbacks, and Significant Recent Developments in Mechanochemistry: A Perspective View

Although known since antiquity, mechanochemistry has remained dormant for centuries. Nowadays, mechanochemistry is a flourishing research field at the simultaneous stages of gathering data and (often astonishing) observations, and scientific argumentation toward their analysis, for which the combination of interdisciplinary expertise is necessary. Mechanochemistry’s implementation as a synthetic method is constantly increasing, although it remains far from being fully exploited, or understood on the basis of fundamental principles. This review starts by describing many remarkable advantages of mechanochemical reactions, simplifying and “greening” chemistry in solutions. This description is followed by an overview of the current main weaknesses to be addressed in the near future toward the systematic study of its energetics and chemical mechanisms. This review finishes by describing recent breakthrough experimental advances, such as in situ kinetics monitoring using synchrotron X-ray powder diffraction and Raman spectroscopy, plus equally significant computational chemistry approaches, such as quantum mechanochemistry, used for the understanding of covalent or hydrogen bond ruptures in biomolecules or mechanophores in polymers at the single-molecule level. Combined with new technologies to control temperature and pressure in ball mills, these appealing new methods are promising tools for establishing the fundamental knowledge necessary for the understanding of mechanochemical reactivity and mechanisms

Methyl gallate

The crystal structure of the title compound (systematic name: methyl 3,4,5-trihydroxy­benzoate), C8H8O5, is composed of essentially planar mol­ecules [maximum departures from the mean carbon and oxygen skeleton plane of 0.0348 (10) Å]. The H atoms of the three hydroxyl groups, which function as hydrogen-bond donors and acceptors simultaneously, are oriented in the same direction around the aromatic ring. In addition to two intra­molecular hydrogen bonds, each mol­ecule is hydrogen bonded to six others, creating a three-dimensional hydrogen-bonded network

WinPSSP: a revamp of the computer program PSSP and its performance solving the crystal structures of small organic compounds and solids of biological and pharmaceutical interest

The direct-space methods software Powder Structure Solution Program (PSSP) [Pagola & Stephens (2010). J. Appl. Cryst. 43, 370-376] has been migrated to the Windows OS and the code has been optimized for fast runs. WinPSSP is a user-friendly graphical user interface that allows the input of preliminary crystal structure information, integrated intensities of the reflections and FWHM, the definition of structural parameters and a simulated annealing schedule, and the visualization of the calculated and experimental diffraction data overlaid for each individual solution. The solutions are reported as filename. cif files, which can be used to analyze packing motifs and chemical bonding, and to input the atomic coordinates into the Rietveld analysis software GSAS. WinPSSP performance in straightforward crystal structure determinations has been evaluated using 18 molecular solids with 6-20 degrees of freedom. The free-distribution program as well as multimedia tutorials can be accessed at http://users.uoi.gr/nkourkou/winpssp/

Tetrathiafulvalene: A Gate to the Mechanochemical Mechanisms of Electron Transfer Reactions

This report describes aspects of our previous studies of the mechanochemical synthesis of charge transfer complexes of the electron donor tetrathiafulvalene, which are relevant to the use of laboratory X-ray powder diffraction for ex situ monitoring of mechanochemical reactions toward investigating their mechanisms. In particular, the reaction of tetrathiafulvalene and chloranil was studied under neat mechanochemical conditions and liquid-assisted grinding with diethyl ether (1 μL/mg). The product in both cases is the green tetrathiafulvalene chloranil polymorph and the mechanism of the redox reaction is presumably the same. However, while the kinetic profile of the neat mechanochemical synthesis was fitted with a second-order rate law, that of the overall faster liquid-assisted grinding reaction was fitted with the Ginstling-Brounshtein 3D diffusion-controlled model. Hence, the diffusional processes and mass transfer bringing the reactants together and separating them from products must be different. Diffraction measurements sensitive to crystalline phases and amorphous material, combined with in situ monitoring by spectroscopic techniques, will ultimately afford a better understanding of mechanochemical reaction mechanisms, a hot topic in mechanochemistry

Poly[l-2-aminopyrazine-j2 N1 :N4 - l-cyanido-copper(I)]: A Three-dimensional Network From Laboratory Powder Diffraction Data

In the title compound, [Cu(CN)(C4H5N3)]n or [Cu(-CN)(-PyzNH2)]n (PyzNH2 is 2-amino­pyrazine), the CuI center is tetra­hedrally coordinated by two cyanide and two PyzNH2 ligands. The CuI-cyano links give rise to [Cu-CN] chains running along the c axis, which are bridged by bidentate PyzNH2 ligands. The three-dimensional framework can be described as being formed by two inter­penetrated three-dimensional honeycomb-like networks, both made of 26-membered rings of composition [Cu6(-CN)2(-PyzNH2)4]

Chemical Kinetics of the Mechanochemical Synthesis of Tetrathiafulvalene Chloranil

A large variety of materials can be prepared from powdered reactants by solid-state grinding and mechanochemistry, avoiding or largely reducing the use of reaction solvents, so offering alternative green chemistry synthetic routes. However, the mechanisms of such reactions are poorly understood, and their properties have only recently started to be unraveled. As part of a 2019 PURS project, our group studied the chemical kinetics of the mechanochemical synthesis of tetrathiafulvalene chloranil (green polymorph), a charge transfer complex with ionicity around 0.3e-. The electron transfer reaction between tetrathiafulvalene (electron donor) and chloranil (electron acceptor) was carried out by manually grinding stoichiometric quantities of the reactants in 1:1 molar ratio under isothermal conditions. The fraction of product obtained was monitored by quantitative phase analysis from laboratory X-ray powder diffraction using the internal standard method. Current results indicate a reaction order solid-state mechanism and a second-order rate law for the neat mechanochemical synthesis. An increased rate constant is observed for the same reaction by liquid-assisted grinding using diethyl ether as a liquid additive

Mechanochemical Conversions Between Crystalline Polymorphs of a Complex Organic Solid

We report the conversion between three crystalline polymorphs of a capped amino acid, N-acetyl-l-phenylalanyl-NH2, using mechanochemistry, with conversion between the α and γ polymorphs being reversible, depending on the milling conditions used. Solvent drop grinding of the α and β polymorphs with water yields the γ polymorph, whereas dry grinding of the β or γ polymorph yields the α polymorph. The α and β polymorphs are also accessible from solution (from methanol and water, respectively), and their structures were solved from single crystal diffraction data. The γ polymorph, so far only accessible mechanochemically, was solved and refined from powder X-ray diffraction data. The polymorphs show various degrees of crystallographic disorder, and the numbers of crystallographically independent molecules vary. These observations are supported by 13C and 15N magic angle spinning solid-state NMR data. Possible reasons for the formation of multiple polymorphs and their respective stability as a function of Z′, degree of disorder, and molecular shape and conformation are discussed. The results have implications for understanding the accessibility of new polymorphs of complex, low-symmetry organic solids with multiple dihedral degrees of freedom

TTF-DDQ: Two "Green'' Synthetic Routes, Crystal Structure and Band Gap from FT-IR Spectroscopy

International audience[No abstract