Hydrogen bonds structure-property relations

Keywords Hydrogen bond structure-property relation phase transition critical temperature ... 

In most cases, the property of a hydrogen-bonded substance is not directly related to the hydrogen-bond structure. Such relations are beyond the scope of this chapter however, a few examples will be given below for illustration. The very spectacular properties are those of colour changes. 

MOLECULAR STRUCTURE-PROPERTY RELATIONS Table 4.5 The effect of hydrogen bonds... 

A classification of crystals based on bonding is useful in understanding structure-property relations in solids. Five types of solids are readily defined on bonding considerations ionic, covalent, metallic and molecular (van der Waals) and hydrogen-bonded. In Table 1.2, the important characteristics of the five types of solids are presented. In real situations, however, solids may exhibit features of more than one type of bonding. 

STRUCTURE-PROPERTY RELATIONS FOR HYDROGEN-BONDED SOLIDS... 

Below, the interdependence of macroscopic properties on these microscopic features is described briefly for 0H---0 hydrogen-bonded crystals. The bistable homonuclear hydrogen bonds are convenient examples to explain the structure-property relations, because the H atom is readily locatable in the structure in this way the mechanism of microscopic transformations can be followed. At the same time, H-bonded systems are important for understanding transformations of molecular and biological systems, or for prospective practical applications. At present there appear to exist no practical applications of electronic devices based on hydrogen-bonded materials. 

The structure-property relations discussed here have been observed in NH- - -N bonded crystals, and are connected with the transformations of these hydrogen bonds (Szafratiski Katrusiak, 2007 Katrusiak Szafratiski, 2006). These transformations have significant consequences for the dielectric properties of the crystals. 

Complexes. The structure of an n a charge-transfer complex between quinoxaline and two iodine atoms has been obtained by X-ray analysis and its thermal stability compared with those of related complexes. The hydrogen bond complex between quinoxaline and phenol has been studied by infrared spectroscopy and compared with many similar complexes. Adducts of quinoxaline with uranium salts and with a variety of copper(II) alkano-ates have been prepared, characterized, and studied with respect to IR spectra or magnetic properties, respectively. 

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