Electron homologous series phases

FIGURE 18 Electron diffraction patterns of the homologous series phases of the lanthanide higher oxides. 

A recent study combined quantum chemical calculations and electron diffrac-tion/photoelectron spectroscopy to derive the following dialkylzinc gas phase enthalpies of formation ethyl, 57 8 n-propyl, 10 8 isopropyl, 32 8 f-butyl, —17 8 neopentyl, — 117 8 kJmoF. The benchmark value of 53 1 kJmol was chosen for the gas phase enthalpy of formation of dimethylzinc. Compared to the experimental values, the diethyl and dineopentyl values are very close, but the w-propyl enthalpy of formation is just barely within the combined large error bars. The methylene increment from the theoretically derived values of diethylzinc and di-n-propylzinc is —23.5 kJ mol , a value that is consistent with other gas phase homologous series. Using this increment, the enthalpies of formation of gaseous di-w-butylzinc and di-n-pentylzinc are calculated to be —37 and —84 kJmoU, respectively. 

Of the 15 experimentally known phases of the higher oxides only five of them have been determined by X-ray and neutron diffraction using the Rietveld refinements method. To understand the thermodynamic behavior and phase reactions it is helpful to have a model of the undetermined structures. Using the experimental electron diffraction data it is possible to determine the symmetry of the unit cell and develops a transformation matrix between the fluorite and ten of the intermediate phases as shown in Table 2. The module theory provides a method for modeling the unknown structures of the homologous series of the lanthanide... 

This density profile shows a wide maximum in its middle (z = d/2) which represents the region of mesogenic cores. Another secondary maximum (z = 0) is observed in between the sublayers of mesogenic cores. This secondary maximum arises from the backbones which have a relatively large electron density because they have silicon atoms. Therefore, the backbones appear squeezed between the sublayers of mesogenic cores so that the structure of this SmA phase may be described in terms of microphase separation . This is the situation depicted in Fig. 9a. Moreover, Fig. 10 also shows that adding aliphatic parts to the macromolecule helps the backbone to resist the confinement. Nevertheless, one should not conclude that all the SmA phases of LCPs can be described in this way. For instance, in the same homologous series, polymer P4 j shows only one order of smectic reflection so that p(z) is sinusoidal and the backbones are not confined at all (Fig. 9b). 

I synthesized the S phase and obtained information on the unit cell of the S phase by electron microscopy. Professor Eyring told me the story of the 8 phase in the terbium higher oxides. At that time the formula of the oxygen-deflcient fluorite-related homologous series of the rare earth higher oxides was R 02 -2, and that there are two families when n is odd the... 

Powder diffraction studies of many of the phases were carried out by Sawyer et al. (I965b). Unit cells of many members of the homologous series have been determined by electron diffraction by Kunzmann and Eyring (1975). They are listed in table 27.1 and shown projected on the (2ll) in fig. 27.8. 

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