Caged structures adamantanes

Adsorption of a condensed 1-hydroxy-adamantane layer at the Hg elec-trode/(Na2S04 or NaF) solution interface has been studied as a function of temperature by Stenina et al. [174]. Later, Stenina etal. [175] have determined adsorption parameters and their temperature dependence for a two-dimensional condensation of adamantanol-1 at a mercury electrode in Na2S04 solutions. They have also studied coadsorption of halide (F , Cl , Br ) anions and 1-adamantanol molecules on Hg electrode [176]. More recently, Stenina etal. [177] have described a new type of an adsorption layer comprising organic molecules of a cage structure condensed at the electrode/solution interface. This phenomenon was discovered for adsorption of cubane derivatives at mercury electrode. 

The convenient synthesis of adamantane [26] led to several significant developments. 1 -Adamantyl substrates (54, Scheme 2.19) are tertiary alkyl compounds for which the caged structure prevents rear-side nucleophilic attack, and elimination does not occur because adamantene (55) is too highly strained. The following question arises when does product formation occur in the solvolytic process Product studies from competing nucleophilic substitutions in mixed alcohol-water solvent mixtures have provided an answer. To explain the background to this work, we first need to discuss product selectivities. 

The source of the strain in adamantane is not readily apparent but appears to be due to features present in the rigid, cage structure of the molecule. Less rigid molecules, e.g. acyclic alkanes, cyclohexane and /nms-decalin, are free to relax and to adopt conformations in which the best balance between angle, nonbonded and torsional strain is achieved. Thus, C-C-C bond angles of 112.4... 

Hexamethylenetetramine is a co-polymer (oligomer really such as those we met in Chapter 52) of formaldehyde and ammonia containing six formaldehyde and four ammonia molecules. It has a beautifully symmetrical cage structure belonging to the adamantane series. 

In addition to the simple tetrahedral shape, other geometries can be chiral. For example, adamantane is a caged structure in which four bonds project to the comers of an expanded tetrahedron consequently, suitably substituted adamantanes may be optically active. This example illustrates clearly that chirality is a molecular property, rather than an atomic one. 

Figure 6 Adamantane-Uke cage structure of [M4 (SPh) 10] (phenyl groups omitted) determined with the Cd , Zn , and Co ions. (Reprinted with permission from Ref. 41. 1982 American Chemical Society)...

Partial pressures of SiS and other sulphur species were measured over the temperature range 991—1122 K and used to compute the standard free-energy change of the reaction. The molecular and crystal structures of tetra(methyl-germanium)hexasulphide have been determined. The crystals are monoclinic, space group C2/c, with a — 9.422, b — 16.779, c = 10.708 A 107.94 , and Z = 4. The molecule was found to adopt the adamantane (3) rather than the open-cage structure (4), both of which have previously been... 

The 0 types form cage structures and are not macromolecular. Examples of this class are adamantane and builvalene. 

A bicyclic cage derivative, P4(NMe)6, can be made below 20°C from methylamine and phosphorus trichloride (7.287). This compound is insoluble in water but soluble in many organic solvents. A highly symmetrical adamantane-type cage structure is indicated by both x-ray analysis and by NMR which shows a single resonance peak. 

The isopropyl derivative P4(NPr )e can have an alternative cage structure (7.289). On further heating this reverts to the more stable adamantane-type structure (7.287) [24]. 

The unique structure of adamantane is reflected in its highly unusual physical and chemical properties, which can have many applications in nanotechnology, as do the diamond nanosized crystals, with a number of differences. The carbon skeleton of adamantane comprises a cage structure, which may be used for encapsulation of other compounds, such as drugs for drug delivery. Because of this, adamantane and other diamondoids are commonly known as cage hydrocarbons. In a broader sense they may be described as saturated, polycyclic, cagefike hydrocarbons. 

Later, the name diamondoids was chosen for all the higher cage hydrocarbon compounds of this series because they have the same structure as the diamond lattice highly symmetrical and strain-free so that their carbon atom structure can be superimposed on a diamond lattice, as shown in Fig. 5 for adamantane, diamantane, and triamantane. These compounds are also known as adamanto-logs and polymantanes. 

The tetrameric zinc anion [Zn4(//-ScPh)r,(ScPh)4]2 has been structurally characterized as the first example of a Zn4Se4 adamantane cage-type structure.594 A further example was characterized by Bochmann and co-workers as part of a study of polymetallic zinc selenophenolates, in this case with chlorides replacing the terminal selenophenolates, [Zn4(/u-SePh)6Cl4]. Octameric zinc species were also characterized with either chloride or phosphine ligands resulting in anionic and neutral complexes respectively, [Zn8(/x-SePh)12Cl4]2 and Zn8(yu-SePh)12(SePh)2 (P Pr3)2.301... 

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