Correlation between Molecular and Crystal Properties

Molecular Packing and Correlations between Molecular and Crystal Properties... 

Correlation between molecular and crystal properties Fact or fiction ... 

All bivariate correlations between molecular and crystal properties are only broad and approximate, demonstrating that crystal packing is a complex phenomenon. More often that not, one finds that correlations expected on the basis of simple reasoning do not in fact hold. For example. Fig. 8.10 shows that there is no relationship between central molecular dipole moments and point-charge coulombic lattice energies, not even when both quantities are calculated by the same method (the rescaled EHT method). This is a further confirmation that central dipoles are a very poor indicator of molecular electrostatic properties [27]. 

Both in bivariate and multivariate analysis, correlations between molecular and crystal properties are poor, unsure, and scarcely robust. The fundamental reason is that crystal packing is a matter of finely adjusted detail, and global indicators will never reach the subtleness required for a real predictive power. 

The idea is that X must govern in some way all properties of the interface, including the permittivity. The latter includes an electronic and a molecular term, which have been tentatively separated7 on the basis of model approaches. In this chapter, only the correlation of the capacitance with X is relevant. The correlation between 11C and tX has been demonstrated for eight metals in aqueous solution. It has been shown26,34 that the correlation derived from sp-metals is fit also by single-crystal faces of sd-metals. In particular, the capacitance of Ag increases in the sequence... 

Despite the vast number of reported syntheses, crystal structures, properties and applications of monomeric Pcs, it is still difficult to clarify clearly the synthetic mechanisms of Pcs in various conditions, to predict fully the supramolecular structures of Pcs in the solid state (except for a very few types of simple Pcs), and to elucidate completely the correlation between molecular structure and properties. The large-scale preparation and separation of some novel Pcs with interestingly properties is still very hard. On the basis of the great potential applications of Pcs in high-tech fields, exploitation of multi-functional Pc materials needs to be strengthened in the future. There is still plenty of room for further investigation of Pc chemistry. 

The correlation between molecular structure, liquid crystal transition temperatures and physical properties of the nematic phase of these materials of relevance to individual types LCDs is dealt with extensively in Chapter 3. 

An understanding of the correlation between molecular structure and physical properties of thermotropic mesogens is important to optimize parameters such as the operating temperature range of liquid crystal displays. 

Until 1982 Schadt and coworkers successfully developed experimental techniques for reliably determining all relevant liquid crystal material parameters, i.e., optical An = (nil and dielectric anisotropy Ae = (fn — l), splay (A h), twist ( 22) and bend ( 33) elastic constants, viscosity constants (//, y,), etc. This provided the basis for searching for correlations between molecular structural elements, LC material properties, and display performance [12, 16,17]. Figure 1.2 illustrates an example... 

Abstract In this chapter, recent progress in the synthesis, crystal structures and physical properties of monomeric phthalocyanines (Pcs) is summarized and analysed. The strategies for synthesis and modification of Pcs include axial coordination of central metal ions, peripheral substitution of Pc rings and the ionization of Pcs. The crystal structures of various typical Pcs, especially the effects of different synthetic and modification strategies on the supramolecular assemblies of Pcs via %—% interactions between Pc rings, are discussed in detail. Finally, the UV-vis spectroscopic, conducting, magnetic and catalytic properties of some Pcs with crystal structures are presented briefly, and the correlations between various properties and the molecular structure discussed. 

With the rapid development of modem analysis techniques, especially the popularization of single-crystal X-ray diffraction equipment, the origin of various physical and chemical properties, and the clear elucidation of correlations between the structure and properties of Pcs have become possibilities. Together with the maturity and diversification of their modifications, many Pcs have been synthesized and their molecular structures characterized by X-ray diffraction analysis in the past 5 years [15-77]. 

Raman spectroscopy s sensitivity to the local molecular enviromnent means that it can be correlated to other material properties besides concentration, such as polymorph form, particle size, or polymer crystallinity. This is a powerful advantage, but it can complicate the development and interpretation of calibration models. For example, if a model is built to predict composition, it can appear to fail if the sample particle size distribution does not match what was used in the calibration set. Some models that appear to fail in the field may actually reflect a change in some aspect of the sample that was not sufficiently varied or represented in the calibration set. It is important to identify any differences between laboratory and plant conditions and perform a series of experiments to test the impact of those factors on the spectra and thus the field robustness of any models. This applies not only to physical parameters like flow rate, turbulence, particulates, temperature, crystal size and shape, and pressure, but also to the presence and concentration of minor constituents and expected contaminants. The significance of some of these parameters may be related to the volume of material probed, so factors that are significant in a microspectroscopy mode may not be when using a WAl probe or transmission mode. Regardless, the large calibration data sets required to address these variables can be burdensome. 

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