Results of Crystal Structure Analyses

Single crystals [3-5] of a yellow (27) and a red (28) benzimidazolone pigment have been studied by X-ray diffraction analysis. 

At a first glance, these studies appear to afford results which are comparable to the known data on the crystal structures of monoazo yellow, (3-naphthol, and Naphthol AS pigments  

In the red pigment, these bands consist of a sequence of individual molecules which are interlocked with each other (30). In terms of molecular structure, benzimidazolone pigments thus represent an entirely new type of azo pigment. 

The excellent solvent and migration fastness which is typical of all benzimid-azolone pigments probably results from this singular structural principle, which has not yet been discovered in any other azo pigment class. 

The benzimidazolone moiety, a fundamental feature of all benzimidazolone pigments, is responsible for the high fastness of these pigments to the solvents which are typically found in application media. In this respect, benzimidazolone pigments perform much better than their counterparts in the monoazo yellow and 

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Most papers in the chemical, biological, and material science literature reporting the results of crystal structure analyses include a section (or a footnote) listing the crystal data, which should indicate the quality of the crystal, the form of the experiment, the accuracy of the measurements, and the precision of the results. The journals all have slightly different requirements for the contents of this section the list presented in Table 3 conforms to the most rigorous requirements of the International Union of Crystallography (lUCr) and its journal... 

Angstrom unit The unit of length commonly used in reporting the results of crystal structure analyses. 1 A = 10 cm. It is named after Anders Jonas Angstrom, a spectroscopist from Upsala, Sweden. 

The experimental technique which gives the most accurate structural information about molecules of the size of drug molecules is crystal structure analysis. The precision obtainable in a typical x-ray diffraction experiment is illustrated in Figure 1 (1 ). Bond distances are routinely determined to standard deviations of 0.002 to 0.005 A bond angles to 0.1 to 0.4°. The literature contains the results of thousands of crystal structure analyses (2). These results are contained in the unit cell parameters and the table of x,y,z coordinates of the atoms. Most research-oriented computer centers have computer... 

Here only the results of the structure analyses are presented. Table II shows the crystal data of the two hydrates. Both phases crystallize into the monoclinic system of space group C2/c. There are eight monomeric units and twelve water molecules (the mole ratio is 1/1.5) in the sesquihydrate unit cell, and four monomeric units and eight water molecules (the mole ratio is 1/2) in the dihydrate unit cell. The theoretical values of water content of the crystal lattices are 38.6 wt. for the sesquihydrate and 5-5 wt. for the dihydrate, and these values are accordance well with the observed water contents for a whole sample, ca. i+0 wt.% and more than 5 wt., respectively (Table l). The fiber period is 7.36 A in both hydrates, which corresponds to the length of two monomeric units taking the planar zigzag conformation. 

FIGURE 9. DFT-calculated geometry of S(NMe)3, resulting in a molecule of C k symmetry . This stmcture is known for S(NBu-t)3, and S(NSiMe3)3 from crystal structure analyses Reproduced with permission from Reference 98. Copyright 1998 Wiley-VCH... 

The starting point is the Wurster s Blue radical cation, discovered in 1879 and thoroughly investigated since then The twofold N pyramidal IVWW. /V -tetraalkyl-p-phenylenediamine precursors are completely flattened on two-electron oxidation as proven by crystal structure analyses of the resulting redox salts (Scheme 8a). 

Although blues prepared from unsubstituted uracil, thymine and related bases (e.g., 6-methyluracil, 5,6-dihydrouracil etc.) were the first to be prepared and tested, their composition is the least clear. The author suspects that there is still long way to go to fully understand the nature of these blues . It is possible that there are even blues built on different principles. A main obstacle to the elucidation of Pt blues derived from the unsubstituted pyrimidine nucleobases lies in their versatility as ligands. Not only is there the possibility that these ligands bind to metal ions, specifically Pt, via N(l) or N(3) or (only with uracil) C(5), but also many possible combinations of two or more binding sites, e.g., N(l),0(2) N(3),0(2) N(3),0(4) N(1),N(3) N(3),0(2),0(4) N(1),0(2),N(3),0(4) etc. (Scheme 6). A series of these binding patterns has been established by X-ray crystal-structure analyses [68-70], and others are likely on the basis of spectroscopic studies [71] [72] or from comparison with results obtained for N(l) substituted derivatives. The possibility of different tautomers of platinated forms being... 

Hydrogen-bond energies can be calculated from the results of high precision charge-density X-ray crystal structure analyses. The electron population parameters obtained from high precision low temperature X-ray and neutron Bragg diffraction measurements have been used in a model for molecular interactions to... 

A very informative review of water molecules in hydrated organic crystals was published in 1963 [822]. It reported the results of 62 crystal structure analyses, including the salts of organic cations. By necessity, it was based primarily on analysis of the nonhydrogen distances, X- Ow and Ow A. There was little informa-... 

Of all the physical sciences, Crystallography has benefited the most from the spectacular advances in computer technology in the past decade. The Cambridge Crytallographic Crystal Structure Data Base contains the results of the published crystal structure analyses of organic and organo-metallic compounds. The Protein... 

Although Morgan and Burstall had difficulties in isolating 1 2 complexes of terpy with copper(II), salts of [Cu(terpy)2] are readily prepared with excess terpy 8, 18, 236, 243, 309). Crystal structural analyses of [Cu(terpy)2]X2 (X = NO3 or PFg) have been reported 8,18,309) the cation is Jahn-Teller distorted. As a result of the initial local symmetry, the two terpy ligands become nonequivalent upon Jahn-Teller distortion. ESR studies indicate the presence of a static Jahn-Teller distortion (5, 62, 236). 

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