Crystal structure determination and

Symmetrical cyanine dyes, because of the resonance shown in Figure 6.4 (in which the two contributing structures are exactly equivalent), are completely symmetrical molecules. X-ray crystal structure determinations and NMR spectroscopic analysis have demonstrated that the dyes are essentially planar and that the carbon-carbon bond lengths in the polymethine chain are uniform. The colour of cyanine dyes depends mainly on the nature of the terminal groups and on the length of the polymethine chain. The bathochromicity of the dyes is found to increase... 

Recent developments and prospects of these methods have been discussed in a chapter by Schneider et al. (2001). It was underlined that these methods are widely applied for the characterization of crystalline materials (phase identification, quantitative analysis, determination of structure imperfections, crystal structure determination and analysis of 3D microstructural properties). Phase identification was traditionally based on a comparison of observed data with interplanar spacings and relative intensities (d and T) listed for crystalline materials. More recent search-match procedures, based on digitized patterns, and Powder Diffraction File (International Centre for Diffraction Data, USA.) containing powder data for hundreds of thousands substances may result in a fast efficient qualitative analysis. The determination of the amounts of different phases present in a multi-component sample (quantitative analysis) is based on the so-called Rietveld method. Procedures for pattern indexing, structure solution and refinement of structure model are based on the same method. 

Shannon and Prewitt using data from almost a thousand crystal structure determinations and based on conventional values of 126 pm and 119 pm for the radii of the and F ions, respectively. These values differ by a constant factor of 14 pm from traditional values but it is generally accepted that they correspond more closely to the actual physical sizes of ions in a crystal. A selection of this data is shown in Table 1.9. 

The chirality of metal helicates can be demonstrated experimentally by X-ray crystal structure determinations and in solution by NMR spectroscopy. Addition of chiral shift reagents such as [Eu(tfc)3] (tfc = 3-(trifluoromethylhydroxymethylene)-(+)-camphorato) to selected helicates results in the splitting of some of the ligand signals as a consequence of the formation of diastereomeric complexes with the shift reagent. Such splitting is not observed for the free ligands, which are achiral. 

The crystal structure determinations and spectral data show that the carbonyl oxygen in the 1 1 adducts of trichlorides of the type 329 (R = Aik, Ar) with monodentate donors like pyridine is coordinated intramolecularly to tin723,743 -746. However, the intramolecular coordination can be broken in the 1 2 adducts with monodentate donors and with 1 1 bidentate donors like bipyridine. 

There are only a few experimental data available. One x-ray crystal structure determination and one Huckel MO calculation were reported in CHEC-I. Now there are more theoretical data available. With the AMI SCF-MO method some pyridazino[4,3-c]pyridazine derivatives have been calculated <88JOC3900>. New quantum chemical calculations <90MI 719-01) and some more experimental data are reported <85KGS1428>. 

Smaragdyrin-azobenzene conjugates of the type 80 have been crystal structure determined and studied with respect to their photochemical and electrochemical behavior. It could be concluded that the relatively electron-withdrawing azobenzene moiety is responsible for a corresponding energy transfer to the smaragdyrin 7t-system <2007EJ0191>. 

I would like to thank my advisor Lawrence Barton for his assistance during this project, Professor Nigam P. Rath for the crystal structure determination and funding from the NSF, the ACS-PRF and UM-St. Louis. 

The tropolones form transition-metal complexes of high affinity constants, for example [M(77 )3] with M = Co(n), Ni(H) and Zn(H), but M(77 )2 with M = Cu(II)2 . Moreover, these compounds form complexes with heavy metals (Os, Ir, Pt, Mo and W) , the lanthanides(in) and main-group metal ions (Ga, In, Sn, Sb and Pb) many have crystal structures determined and some show biological activities and potential... 

Crystallization of multiple component crystals with a stoichiometric relationship is a result of competing molecular associations between similar molecules, or homomers, and different molecules, or heteromers. To date most studies on cocrystals focus on the isolation of cocrystals for crystal structure determination, and the variables that control crystallization kinetics have not been explicitly considered. Cocrystals have been prepared by solution, solid-state, or melt processes largely based on trial and error. This section will focus on the mechanistic and kinetic aspects for cocrystal formation by solution and by solid-state processes. 

Information that is put into this Database is derived from published reports of crystal structure determinations. The data extracted from the scientific literature in this way include the atomic coordinates, information on the space group, chemical connectivity, and the literature reference to each structure determination. Each compound listed in the Database is identified by a six-letter code (the REFCODE), unique to each crystal structure determination. Duplicate structures and remeasurements of the same crystal structure are identified by an additional two digits after the REFCODE. Scientific journals are scanned regularly by the Database staff for reports of crystal structure determinations, and the data are then entered into this Database. Structural data are also deposited by journals, for example. Chemical Communications, that publish articles, but do not have space for atomic coordinates. All crystallographic data reported in the literature are tested by the Database staff for internal consistency, precision, and chemical reasonableness. In... 

Thus, a fast experiment is routinely suitable for evaluation of the specimen and phase identification, i.e. qualitative analysis. When needed, it should be followed by a weekend experiment for a complete structural determination. An overnight experiment is required for indexing and accurate lattice parameters refinement, and a weekend-long experiment is needed for crystal structure determination and refinement. In some instances, e.g. when a specimen has exceptional quality and its crystal structure is known or very simple, all relevant parameters can be determined using data collected in an overnight experiment. Similarly, fast experiment(s) may be suitable for unit cell determination in addition to phase identification. In any case, one should use his/her own judgment and experience to assess both the suitability of the experimental data and the reliability of the result. 

Sir2004/CAOS S1R2004 an improved tool for crystal structure determination and refinement, M. C. Sir2004 CAOS... 

C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori and R. Spagna, J. Appl. Crystallogr., 1999, 32, 115 119 and SIR2004 an improved tool for crystal structure determination and refinement, M. C. Burla,... 

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