Double wheel structure

Schmidbaur. H. Hartmann, C. Reber. G. Muller, G. Isovalent and mixed-valent ylide complexes of gold The synthesis of trinuclear compounds having double paddle-wheel structure. Angew. Chem.. Int. Ed. Engl. 1987. 26. 1146. 

Work during the 1960s on the CB Pressurized Pod resulted in the standardization of the M51 Shelter System in 1971. The unit was an easily transportable, pressurized enclosure. It could be air-dropped or towed to provide protection from chemical and biological agents in the field for combat, combat support, and combat service support troops. The M51 was a double-walled, air-inflated, self-supporting shelter and airlock structure. When erected, the shelter was semicircular in cross-section with a maximum inside height of 7.5 ft, with inside dimensions of 15 x 14 ft. An airlock entrance (with a set of double doors at each end) on the front was 11 (1) x 4.2 (w) x 6.7 (h) ft in dimension. The filter and support equipment were mounted on a two-wheeled trailer.186... 

The extension of the endo-aSsy rule allowed the formation of the first examples of oriented handcuff pseudorotaxane architectures with a predefined stereochemistry [27]. With respect to the use of a single calixarene, a further synthetic challenge is represented by the use of a double-calixarene like 20 (Fig. 30.13), because of the inherent difficulty in controlling the relative orientation of the wheels within the entire pseudorotaxane system. In fact, the threading of 20 with a bis-ammonium axle (e.g., 14 and 17 ) could give rise again to the three stereoisomeric handcuff pseudorotaxane structures, [27] with the two calix-wheels in three different relative orientations, head-to-head HJd) (I), tail-to-tail (T,T) (II), and head-to-tail (H,T) (III) (Fig. 30.13). 

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