Progresses in the fundamental aspects of treating the electron-electron interaction in solids and practical methods for solving the Schroedinger equations enable us to predict the crystal structures theoretically. Some basic aspects and examples are reviewed. Brief comments will also be made on the future problems.
Ab initio prediction of crystal structures from molecular formulae has long been one of the challenges for computational chemistry. Three major obstacles that have retarded progress in this area are redundancy of polymorphism, accuracy of energy functions, and excessive demand for computer resource. The state of the art in the crystal structure prediction is explained in some detail using the best commercial package. A few other algorithms are briefly mentioned as well. Finally the importance of improving the intermolecular potential function is emphasized and a promising method for achieving the goal, called inverse probability density function method, is presented.
Recent development in computer simulation of structure and physical properties of polymer crystals has been reviewed. Importance of combining simulation technique with X-ray analysis method was emphasized in the elucidation of crystal structure of polymers consisting of small crystallites with more or less irregular structure. Several examples were given for conformational analysis of polymer chains, determination of chain packing structure, and prediction of mechanical property as a function of temperature.
An unexpected protein-fold evolution via natural selection was found in the crystal structure of congerin I, a congar eel galectin. This particular example suggests that the relationship among protein-folds should be studied not only by stereochemistry but also by phylogenetics. How can we predict entire fold models exist in the protein-fold space and their relationships? The outline and the preliminary results from an attempt for mapping the protein-fold space by a computer simulation are described.
Synchtrotron X-ray powder diffraction and latest analysis software have increased possibilities of solving unknown structures. This article describes (a) estimation of integrated intensities by step-by-step Le Bail refinements, (b) derivation of an initial structural model by the direct method, and (c) analysis of a disordered structure by MEM-based pattern fitting. Examples of analyses with synchrotron powder data, cimetidine for (a), zeolite Linde Type L for (b), and Sr9.3Ni1.2 (PO4) 7 for (c), are shown.
The concept of heat capacity is reviewed, and the important role of heat capacity in thermodynamic studies of materials is explained in detail. The relationship between the structure of crystals and the properties of the materials is considered. Thermodynamic properties are described with some examples from new reports.
Molecular conductors exhibit a variety of physical properties which can be systematically understood on the basis of their simple and clear electronic structures. The simple tight-binding band calculation is quite useful (but not almighty) to describe their electronic structures. Depending on arrangement and orientation of the molecule, the electronic structure of the molecular conductors is full of variety.
Paramagnetic centers have either ferro or antiferromagnetic interactions, and the magnetic interactions induced by charge transfer interactions were called as the superexchange mechanism. The magnetic interaction in metal complexes can be controlled by molecular designs, in which the metal to ligand or ligand to metal charge transfer interactions are taken into account.
Correlation between crystal and electronic structures in dithioketopyrrolpyrrole pigment (DTPP) has been reviewed on the basis of the molecular exciton theory as well as on the polarized reflection measurements on single crystals. The mechanism of the near-IR absorption of DTPP has been clarified as arising from the molecular arrangement of “bricks in a brick wall” structure as characterized by J-aggregates in cyanine dyestuffs.
Dihydroxysilicon phthalocyanine [Si (OH) 2Pc] as a carrier generation material for photoreceptors was investigated by using X-ray diffraction and computational chemistry. The crystal structures of Si (OH) 2Pc three polymorphs (Phase I, II and III) were determined from powder X-ray diffraction data. Phase II and III show suitable photosensitivity for laser printers, while Phase I has no sensitivity. We discuss the photoconductivity of Si (OH) 2Pc from the crystal and the electronic structures.
X-ray crystallographic study on photochromic crystals has been introduced. Although a number of photochromic materials have been reported, compounds which show photochromic reactivity in the crystalline phase are very rare and detailed X-ray crystallographic study on the crystalline photochromism is limited, because of the difficulty to increase the conversion rates in the crystals. Recently, in situ X-ray crystallographic analysis has been successfully carried out for N-salicylideneaniline, hexaarylbiimidazole, and diarylethene, by employing new phototechniques, such as two-photon excitation or linear-polarized light illumination. This paper reports on such direct X-ray structural analysis of diarylethenes as well as N-salicylideneanilines.
The design of the crystal structure of organic solids and the control of their reactivity are important for crystal engineering, which is the planning of the properties and functions of crystalline materials. Here we describe recent studies on the organic reactions that proceed in the crystalline state including the topochemical polymerization of diene monomers such as muconic and sorbic acid derivatives.
Recent progress of X-ray crystal structure analysis enables us to “see” the dynamic processes in crystal. The crystalline-state reaction is one example by which chemical reaction pathway and structure of reaction intermediate can be studied. Two ways to “see” the reaction intermediates in crystal, i.e. the time-resolved measurement and freeze-trapping of reaction in-termediates, are mainly used for in situ observation of crystalline-state reaction. By using the freeze-trapping strategy, crystal structure of triplet carbene was analyzed. In this kind of study, special techniques should be applied carefully in every step in the irradiation of specimen crystal, X-ray diffraction measurement, and structure refinement.
The morphology (growth habit) of a crystal depends on the relative growth rates of different crystal faces which are determined by both structural and environmental factors. In protein crystals, where the constituent molecules are large and contain considerable amount of water, molecules form intermolecular contacts (macrobond) of various strength depending on the nature of protein molecules and their crystal forms. The at first sight complex structure of intermolecular contact in protein crystals can be reduced in a simple periodic bond chain of macrobonds. We estimated the strength of intermolecular contact in protein crystals and studied their correlation to the crystal morphology.
Three-dimensional structures are correlated with their thermostability. Sudies on structures of thermophilic and chimeric 3-isopropylmalate dehydrogenases make it possible to discuss their thermostability in relation with their enthalpies.