Polymorphism structural aspects, polymorphic systems

In the best-designed studies of polymorphic or solvate systems, the purpose of the vibrational spectroscopy investigation should be to gather information from the observed pattern of vibrational frequencies and to use these data to understand the structural aspects that yield crystallographic differences. Once suitable spectral features are identified from this work, they can be used to develop easily performed methods for the quantitative analysis of one polymorph (or solvate) in the presence of the other. Unfortunately, all too many workers are merely... 

This book represents an attempt to summarize the major issues pertaining to the pharmaceutical aspects of polymorphism, as well as the effects of solvate formation. The book is subdivided into five main sections, the first consisting of two chapters defining the phenomenon. Chapter 1 presents the theory and origin of polymorphism in solids, and Chapter 2 examines the phase characteristics of polymorphic systems in the systematic manner permitted by the Phase Rule. The second section covers the crystallographic considerations that define different polymorphic and solvate species, with Chapters 3 and 4 providing detailed summaries of the structural aspects. 

This report describes some recent developments in the understanding of the thermodynamic, kinetic and structural aspects of organic crystal polymorphism with an emphasis on the application of newer methodology used for its study, since this is one of the areas in which significant progress has been made in recent years. Numerous examples of polymorphic systems are described to illustrate the applications of both older and newer techniques for their investigation. These include studies of pseudopolymorphism manifested by hydrates and solvates of the parent organic molecule. Finally, the crucial question of... 

Microporous materials with regular pore architectures comprise wonderfully complex structures and compositions. Their fascinating properties, such as ion-exchange, separation, and catalysis, and their roles as hosts in nanocomposite materials, are essentially determined by their unique structural characters, such as the size of the pore window, the accessible void space, the dimensionality of the channel system, and the numbers and sites of cations, etc. Traditionally, the term zeolite refers to a crystalline aluminosilicate or silica polymorph based on comer-sharing TO4 (T = Si and Al) tetrahedra forming a three-dimensional four-connected framework with uniformly sized pores of molecular dimensions. Nowadays, a diverse range of zeolite-related microporous materials with novel open-framework stmctures have been discovered. The framework atoms of microporous materials have expanded to cover most of the elements in the periodic table. For the structural chemistry aspect of our discussions, the second key component of the book, we have a chapter (Chapter 2) to introduce the structural characteristics of zeolites and related microporous materials. 

An extremely important tool for the characterization of polymorphs and solvates is that of microscopy, since the observable habits of differing crystal structures must necessarily be different and therefore useful for the characterization of such systems [27]. Common sense would dictate that the visual observation of such materials would immediately follow an x-ray crystallographic study, which would in principle make the science of optical crystallography [28-30] an essential aspect of any program of study. A review of crystallography from the pharmaceutical viewpoint is available [31]. 

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