Structure studies layered hosts

The atomic positions of the host Ni(NCS)2(4-MePy), molecules were easily found and refined. The molecules adopt a four-blade propeller shape and are asymmetric the conformations being close to those found in previously studied layered clathrates (ref. 2 and 3) the packing of the molecules in the crystal structures being essentially the same as well. However, determination of positions of the guest molecules presented difficulties. In particular ... 

The layered guest-host structures that can also develop undergo a structural evolution more reminiscent of the intercalation process in 2D layered materials (e.g., graphites or silicates). In this case, quasi-2D galleries open up between stacked sheets of the polymers chain as shown in Fig. 25.8. This type of ordering has often been reported in structural studies [84-89] using molecular dopants. Systems showing evidence of layered structures include iodine-doped PA [86] and AsF.s-doped PPV [87]. These layered structures may occur either alone or in combination with channel formations [85,89]. 

The structure of alumina on NiAl(l 1 0) was the subject of a surface X-ray diffraction study by Stierle et al. [46]. The model derived by Stierle et al. from the analysis of the X-ray diffraction data was based on a strongly distorted double layer of hexagonal oxygen ions, where the Al ions are hosted with equal probability on octahedral- and tetrahedral-coordinated sites the resulting film structure was closely related to bulk k-A1203. An attractive feature of Stierle s model was that it provided a natural explanation of the domain structure of the alumina overlayer, which is induced by a periodic row matching between film and substrate lattices. However, as pointed out recently by Kresse et al. [47], this structure model has two bonds with... 

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