Alkyl compounds diffraction studies

Only a limited number of structural studies have been reported on beryllium compounds. The simple alkyls appear to be polymeric with chain structures as shown in XVI (109). For comparison, the structure of di-(t-butyl)beryllium (XVII) is shown as determined from electron diffraction studies (6). In this case, the compound is a linear monomeric species with a Be—C bond length of 1.699 A. Similarly, dimethylberyl-lium has a Be—C bond distance of 1.70 A in the gas phase (5). Comparison of these beryllium structures with the polymer shows that the Be—C distance in the bridge is considerably greater than that in a normal Be—C single bond, a result similar to that observed for the aluminum derivatives. 

Bis(pentametiiylcyclopentadienyl)actinide(IV) mono- and dialkyl complexes are readily prepared from Cp 2 Cl2. A rather large number of alkyl groups have been employed, and compounds of this class are generally prepared by metathesis (equation 59). In the solid state, complexes of formula Cp 2" n 2 adopt a pseudotetrahedral coordination geometry about the actinide metal. A neutron diffraction study of the thorium neopentyl complex Cp 2Th(CH2-t-Bu)2 also revealed agostic Th-H-C interactions with the q -CH bonds. ... 

Previously, the molecular structures of many thiuram di- [20-31] (see Fig. 1), mono- [32], trisulfides [33] and thiuram disulfide derivatives, in which R2NC(S)S- groups are linked by polymethylene chains [34], have been determined by single-crystal X-ray diffraction studies. A number of polycrystalline tetralkylthiuram disulfides and their cyclic analogs have also been recently studied by means of solid-state and CP/MAS NMR [31]. Assignments and and chemical shift data for eight (1-8) selected thiuram disulfide compounds and initial dithiocarbamate salts are shown in Table 1. The observed differences in and isotropic chemical shifts for these molecular systems can be attributed to simultaneous manifestation of the inductive effect of alkyl substituents and to the mesomeric effect of the dithiocarbamate groups discussed below. 

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