Crystallization solvate

The solid state structure of (3>S,8 Sj-10-(8-amino-6-azaspiro[3,4]octan-6-yl)-9-fluoro-3-methyl-7-oxo-2,3-dihydro-7//-pyrido[l,2,3-dfe]-l,4-benzoxa-zine-6-carboxylic acid (218) was determined by X-ray diffraction study (98CPB1710). The structure of 6,10-dihydropyrido[2,l-c][l,4]benzoxazine-6,10-dione 219 was established by X-ray diffraction analysis. It contains a crystal solvate with /j-xylene (99MI40). 

Table I. Comparison of the X-Ray Diffraction from PBT Fiber and Crystal-Solvate...

We suggest that both the lamellar and the microfibrillar morphologies are formed by a nucleation and growth process. A low nucleation density of crystal solvates results in a lamellar morphology, whereas a high nucleation density of the crystalline PBT results in formation of microfibrils. 

In a solid-gas reaction involving a molecular crystal, the reactants are respectively the molecules in the crystalUne solid and the molecules in the gas phase and the product is the product crystal, which can be crystalUne or amorphous. Vapour uptake to generate a solvate crystal (e.g. hydration) is a related process. In fact the difference between a crystal solvation process and a solid-gas reaction leading to new molecular/ionic species is mainly in the energetic scale of the processes and in the fact that in solvation processes, molecules retain their chemical identity. On this premise there is a relevant analogy between the uptake of smaU molecules by a nanoporous material [16] and the reaction between a molecular crystal and molecules to yield a co-crystal or a salt (e.g. acid-base... 

The solubility of a solid, provided that it does not form crystal solvates, or solid solutions, with the solvent but remains as a pure solid, and provided again that only dispersion forces are operative, is given approximately by ... 

The observation of Z > 1 may be regarded as a special case of co-crystallisation where the two components are the same as one another. Thus research on high Z structures is closely related to co-crystals, solvates, hydrates etc. Figure 8.48 shows the X-ray crystal structure of a remarkable... 

In light of the variety of behaviour exhibited by solvates, Byrn (1982) has suggested a classification scheme for crystal solvates based on that behaviour, rather than on stability. He proposed that the solvates for which the solvent can be removed from the crystal and added back to the crystal reversibly without greatly changing the X-ray powder diffraction pattern (Section 4.4) would be considered pseudopoly-morphic solvates. Those which undergo a change in structure, as evidenced by a different powder diffraction pattern, would be described as polymorphic solvates. The appellation does not seem to have been adopted by many other workers. 

When some compounds crystallise they may entrap solvent in the crystal. Crystals that contain solvent of crystallisation are called crystal solvates, or crystal hydrates when water is the solvent of crystallisation. Crystals that contain no water of crystallisation are termed anhydrates. 

Crystal solvates exhibit a wide range of behaviour depending on the interaction between the solvent and the crystal stmcture. With some solvates the solvent plays a key role in holding the crystal together for example, it may he part of a hydrogen-honded network within the crystal stmcture. These solvates are very stable and are difficult to desolvate. When these crystals lose their solvent they collapse and recrystallise in a new crystal form. We can think of these as polymorphic solvates. In other solvates, the solvent is not part of the crystal bonding and merely occupies... 

When some dmgs crystallise they may entrap solvent in their crystals and so form different crystal solvates. In some solvates the solvent plays an important role in holding the crystal together. These solvates, called polymorphic solvates, are very stable, and when they lose their solvent they recrystallise in a different crystal form. In other solvates, referred to as pseudopoly-morphic solvates, the solvent is not part of the crystal bonding and merely occupies voids in the crystal. These solvates can lose their solvent more readily and desolvation does not alter the crystal lattice. Solvated and anhydrous forms of a drug differ in... 

Aqueous solutions of ionic compounds Recall that water molecules are polar molecules and are in constant motion, as described by the kinetic-molecular theory. When a crystal of an ionic compound, such as sodium chloride (NaCl), is placed in water, the water molecules collide with the surface of the crystal. The charged ends of the water molecules attract the positive sodium ions and negative chloride ions. This attraction between the dipoles and the ions is greater than the attraction among the ions in the crystal, so the ions break away from the surface. The water molecules surround the ions, and the solvated ions move into the solution, shown in Figure 14.10, exposing more ions on the surface of the crystal. Solvation continues until the entire crystal has dissolved. 

A Partial Phase Diagram and Crystal Solvate for the Poly(p-Phenyleneterephthalamide)/SuUiiric Acid System... 

It is now well established that certain aromatic polyamides form ordered complexes with their solvents (i.e., crystal solvates). A summary of the occurrence of these crystal solvates h s been compiled in a recent review article by lovleva and Papkov. Among the crystal solvates that have been identified jre poly(m-phenylene isophthalamide) with N-methyl-pyrrolidone and with hex methylphosphortriamide poly(p-benz-amide) with sulfuric acid and poly(p-phenylene terephthalamide) (PPTA) with sulfuric acid and with hexamethylphosphortriamide. These solvates are all characterized by a discrete melting point and a crystalline diffraction pattern. 

Although the presence of solvate phases has been established and qualitative phase diagrams have been published, to our knowledge, a detailed model for a pol3nner solvate and its phase behavior has not been presented. At this time we would like to present a partial phase diagram for the poly(p-phenylene terephthalamide) (PPTA)/sulfuric acid system and a model for the crystal solvate formed. In addition the structure of a model complex will be described. 

The solubility method of determining medium effects is more generally applicable. The chemical potentials of a solute MX in saturated solution in solvent S and in water are equal since each is in equilibrium with the same solid phase, provided no crystal solvates are formed (sect. 2.3.1), thus... 

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