Diamondoid compounds

There exist a number of other methods for the separation of diamondoids from petroleum fluids or natural gas streams (1) a gradient thermal diffusion process [54] is proposed for separation of diamondoids (2) a number of extraction and absorption methods [53,83] have been recommended for removing diamondoid compounds from natural gas streams and (3) separation of certain diamondoids from petroleum fluids has been achieved using zeolites [56, 84] and a number of other solid adsorbents. 

While various computational methods disagree on the magnitude of the relative roles of steilcs and hyperconjugation, the 0.9kcal/mol penalty for the gauche conformations is a useful conformational observation that can be transferred to larger systems. For example, such interactions in chair cyclohexane moieties illushate why adamantane and related diamondoid compounds are not completely free of strain. 

As mentioned before, adamantane and diamantane are the first two members in the diamondoid series, and the most prevalent diamondoid compounds in natural gas. Their measured solubilities in methane, ethane, and carbon dioxide, which are three major components of natural gas, have been reported here [15]. The experimental solubilities of adamantane (CioHie) in ethane, carbon dioxide, and methane at 333 K are presented in Table 1.6, whereas solubility data for diamantane (C14H20) in ethane and carbon dioxide at 333 K and in methane at 353 K are presented in Table 1.7. The solubility of diamantane in methane is also reported in Table 1.7. Solubility data are reported in terms of the solute mole fraction y2 in the supercritical phase. The solubility data for adamantane in carbon dioxide produced... 

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. 

These compounds are chemically and thermally stable and strain-free. These characteristics cause high melting points (m.p.) in comparison to other hydrocarbons. For instance, the m.p. of adamantane is estimated to be 269 °C, yet it sublimes easily, even at atmospheric pressure and room temperature. The melting point of diamantane is about 236.5 °C and the melting point of triamantane is estimated to be 221.5 °C. The available melting point data for diamondoids are reported in Table I. 

Little data is reported on tetra-, penta-, and hexamantane and other higher diamondoids. What is available is compiled by ChevronTexaco scientists as reported in Table I. This is possibly due to the fact that of these compounds only anti-tetramantane has been successfully synthesized in the laboratory in small quantities [32, 33]. 

The approach in crystal engineering is to learn from known crystalline structures of, for example, minerals in order to design compounds with desired properties. Crystal engineering is considered to be a key new technology with applications in pharmaceuticals, catalysis, and materials science. The structures of adamantane and other diamondoids have received considerable attention in crystal engineering due to their molecular stiffness, derivatization capabilities, and their six or more linking groups [114-117]. 

The adamantane structure is unique as it combines three annullated cyclohexane subunits in a nearly spherical overall shape and, as such, it can be regarded as a section of the diamond crystal lattice578. Due to this property, adamantane and other diamondoid molecules are popular as model compounds for synthetic and spectroscopic purposes579 780. 

Some crystalline compounds that exhibit diamondoid structures are listed in Table 20.4.1. The rod linking a pair of nodes can be either linear or nonlinear. 

The same reagent converts unsaturated polycyclic compounds to diamondoid cage hydrocarbons.2... 

The use of transition metals or transition metal clusters to act as nodes for the modular self-assembly of diamondoid networks that are sustained by coordinate covalent bonds is also well established. Such architectures are of more than aesthetic appeal. Indeed, such structures have resulted in a class of compound with very interesting bulk and functional properties. Metal-organic diamondoid structures in which the spacer moiety has no center of inversion are predisposed to generate polar networks since there would not be any inherent center of inversion. Pyridine-4-carboxylic acid is such a ligand and bis(isonicotinato)zinc exists as a three-fold diamondoid structure that is thermally stable and inherently polar.33... 

Octahedral coordination polymers remain much less common that their diamondoid counterparts, but a recent report revealed a novel metal-organic coordination polymer, Zn40(BDC)3 (BDC = benzenedicarboxylate) that suggests an exciting future for such compounds.26 Zn40(BDC)3 is a relatively simple and inexpensive... 

In this section, we will focus on coordination compounds with diamondoid frameworks, especially containing copper(I) and silver(I) ions. These ions having d10 electronic configuration are suitable for a tetrahedral metal center in a diamondoid framework. Table V lists the coordination polymers having diamondoid frameworks reported so far, together with other coordination polymers having related frameworks. 

When 4,4 -bipyridine, L60, is used instead of L4o fourfold interpenetrated diamondoid frameworks are obtained for both Cu(I) and Ag(I) ions. The Cu(I) compound [Cu(L60)2]PF6 (136) exists as four independent concatenated diamondoid frameworks with Cu—-Cu separations of 11.16 A. The Cu(I) centers occupy crystallographic 4 positions and hence all Cu-N bonds are identical, 2.034 A. The PF counteranions... 

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