Single-crystal investigations

IZV2670,91PS133). An X-ray single-crystal investigation showed 127 to possess Cs symmetry, with the boron atom out of the plane formed by the other five atoms. 

Obviously the additional work at every stage of a complete single-crystal investigation cannot be justified for every reaction that one might think of studying. Care is required to choose situations where detailed study of one compound, or of a few related compounds, can supply more insight than less detailed studies on a much larger number of systems. 

Leithe-Jasper (1994) reported the single crystal investigations for two compounds with unique structure types NdFe3Sb2, a = 0.42879, c = 2.57048 and NdFe2-xSb2, a = 0.42965, b = 0.42759, c = 2.57887. 

Nd-Pt-Sb. NdPtSb crystallizes with the Caln2 type structure, a = 0.4544, c = 0.7878 (Rossi et al., 1981 powder X-ray diffraction data). For the experimental details, see the LaPtSb. At variance with these data, Wenski and Mewis (1986a) reported the LiGaGe type structure for the NdPtSb compound, a = 0.4535, c = 0.7866 from X-ray single crystal investigation. For the sample preparation, see PrPtSb. 

Although triplet state studies in rigid glasses are more convenient, it must be pointed out that they have yielded far less quantitative and precise data than have the single-crystal investigations (39,45). Initially the disadvantage of single-crystal studies is that suitable host crystals are difficult to find. 

Furthermore, the lack of a support material in single-crystal investigations does not allow for spillover or phase-boundary effects (14). This limitation may be partly overcome by depositing thin oxide films on single-crystal surfaces ( inverse catalysts (14,47,69)), but the geometric and electronic structure of the oxide and of the exposed metal may still be quite different from that of a dispersed catalyst with nominally identical composition. 

For A3MF6 compounds with larger alkali cations, only a few single-crystal investigations are known. It seems to be clear that K3M0F6 and KsWFe crystallize in the cubic elpasolite-type structure, as well as most of the (NH4)3M F6 compounds at room temperature. For (NH4)3ScF6, a monoclinic structure variant has been reported recently. Very complicated superstructures with five-fold axes have been fonnd in different laboratories for some K and Rb componnds (see citation in Ref 33). However, no stracture determinations are known to date. 

The results of all the single-crystal investigations carried out so far for compounds M8[M (CN)e]a xTlzO are in good agreement with the postulated properties of the modified model. Position 4 a (0, 0, 0) of the cubic face-centered unit cell is fully occupied by four ions and... 

A pentahaptofullerene metal complex 71 was obtained upon the reaction of the hexaadduct 72 with TlOEt demonstrating the acidity of the cyclopentadiene (Scheme 13) [74]. A single crystal investigation confirmed the cyclopentadienide character of the complexed five-membered ring. The length of the [6,6]-and [5,6]-bonds in the remaining Cjg moiety are similar to those of monofunc-tionalized Cgg derivatives which is also demonstrated with the crystal structure of 68. 

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