Crystalline solids atomic radius determination

The simplest diamine, hydrazine N2H4 (Table 3), is normally available as the monohydrate. An X-ray structure of the crystalline solid has been determined (there is some doubt as to the correct space group ) as well as an electron diffraction study of the vapor.The structxues of the di(hydrogen fluoride), di(hydrogen chloride) and monoperchlorate crown ether salts are also known. The N—N distance in hydrazine (1.499 A) is an important parameter, as one half this distance is used for the covalent radius of the single-bonded nitrogen atom. 

Figure 1.2 gives the radial distribution function derived from Fig. 1.1. This figure also shows correspondence between the principal peaks and the radial density for the solid crystal. Because of repulsive interactions between atoms, p(r) has zero magnitude out to a radius nearly equal to the atomic radius. At large radii, p r) is equal to ihe bulk density of the liquid. The mean co-ordination number for ihe liquid can be determined from this curve by integration. Table 1.4 gives some comparisons of data obtained from diffraction studies on liquids with the corresponding data for the crystalline solids. In general it is found that...

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