In chemistry, diamondoids are generalizations of the

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

cage molecule known as

adamantane Adamantane is an organic compound with formula C10H16 or, more descriptively, (CH)4(CH2)6. Adamantane molecules can be described as the fusion of three cyclohexane rings. The molecule is both rigid and virtually stress-free. Adamantane is the mo ...

(C₁₀H₁₆), the smallest unit cage structure of the

diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...

crystal lattice In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystal, crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that ...

. Diamondoids also known as nanodiamonds or condensed adamantanes may include one or more cages (adamantane,

diamantane Diamantane (also called congressane) is an organic compound that is a member of the diamondoids. These are cage hydrocarbons with structures similar to a subunit of the diamond lattice. It is a colorless solid that has been a topic of research s ...

triamantane In chemistry, diamondoids are generalizations of the carbon cage molecule known as adamantane (C10H16), the smallest unit cage structure of the diamond crystal lattice. Diamondoids also known as nanodiamonds or condensed adamantanes may include one ...

, and higher polymantanes) as well as numerous isomeric and structural variants of adamantanes and polymantanes. These diamondoids occur naturally in

petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

deposits and have been extracted and purified into large pure crystals of polymantane molecules having more than a dozen adamantane cages per molecule. These species are of interest as molecular approximations of the

diamond cubic In crystallography, the diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, in ...

framework, terminated with C−H bonds.

Examples

Examples include: *

Adamantane Adamantane is an organic compound with formula C10H16 or, more descriptively, (CH)4(CH2)6. Adamantane molecules can be described as the fusion of three cyclohexane rings. The molecule is both rigid and virtually stress-free. Adamantane is the mo ...

(C₁₀H₁₆) *

Iceane Iceane is a saturated hydrocarbon, saturated polycyclic compound, polycyclic hydrocarbon with formula . It has a Cage (enclosure), cage-like molecule, molecular structure, whose carbon skeleton can be viewed as three fused cyclohexane rings in the ...

(C₁₂H₁₈) * BC-8 (C₁₄H₂₀) *

Diamantane Diamantane (also called congressane) is an organic compound that is a member of the diamondoids. These are cage hydrocarbons with structures similar to a subunit of the diamond lattice. It is a colorless solid that has been a topic of research s ...

(C₁₄H₂₀) also ''diadamantane'', two face-fused cages * Triamantane (C₁₈H₂₄), also ''triadamantane''. Diamantane has four identical faces available for anchoring a new C₄H₄ unit. * Isotetramantane (C₂₂H₂₈). Triamantane has eight faces on to which a new C₄H₄ unit can be added resulting in four

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

s. One of these isomers displays a helical twist and is therefore

prochiral In stereochemistry, prochiral molecules are those that can be converted from achiral to chiral in a single step, such as changing one atom. An achiral species which can be converted to a chiral in two steps is called proprochiral. A molecule ha ...

. The ''P'' and ''M''

enantiomer In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

s have been separated. * Pentamantane has nine isomers with chemical formula C₂₆H₃₂ and one more pentamantane exists with chemical formula C₂₅H₃₀ * Cyclohexamantane (C₂₆H₃₀) * Super-adamantane (C₃₀H₃₆) One tetramantane isomer is the largest ever diamondoid prepared by

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

using a keto-

carbenoid In chemistry a carbenoid is a reactive intermediate that shares reaction characteristics with a carbene. In the Simmons–Smith reaction the carbenoid intermediate is a zinc / iodine complex that takes the form of :I-CH2-Zn-I This complex reacts w ...

reaction to attach cyclopentane rings. Longer diamondoids have been formed from diamantane dicarboxylic acid. The first-ever isolation of a wide range of diamondoids from petroleum took place in the following steps: a

vacuum distillation Vacuum distillation or distillation under reduced pressure is a type of distillation performed under reduced pressure, which allows the purification of compounds not readily distilled at ambient pressures or simply to save time or energy. This te ...

above 345 °C, the equivalent

atmospheric boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envi ...

, then

pyrolysis Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology The word ''pyrolysis'' is coined from the Gree ...

at 400 to 450 °C in order to remove all non-diamondoid compounds (diamondoids are thermodynamically very stable and will survive this pyrolysis) and then a series of

high-performance liquid chromatography High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures. The mixtures can origin ...

separation techniques. In one study a tetramantane compound is fitted with

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

groups at the bridgehead positions. This allows their anchorage to a

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

surface and formation of

self-assembled monolayer Self-assembled monolayers (SAM) are assemblies of organic molecules that form spontaneously on surfaces by adsorption and organize themselves into more or less distinct domains (head group, chain/backbone, and tail/end group). In some cases, mole ...

s (diamond-on-gold). Organic chemistry of diamondoids even extends to ''pentamantane''. The medial position (base) in this molecule (the isomer (2,3)4entamantane) is calculated to yield a more favorable

carbocation Carbocation is a general term for ions with a positively charged carbon atom. In the present-day definition given by the IUPAC, a carbocation is any even-electron cation with significant partial positive charge on a carbon atom. They are further ...

than the apical position (top) and simple

bromination In chemistry, halogenation is a chemical reaction which introduces one or more halogens into a chemical compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs ...

of pentamantane ''1'' with

bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...

exclusively gives the medial bromo derivative ''2'' which on hydrolysis in water and DMF forms the

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

''3''.

In contrast

nitrooxylation In organic chemistry, a nitrate ester is an organic functional group with the formula , where R stands for any organyl group. They are the esters of nitric acid and alcohols. A well-known example is nitroglycerin, which is not a ''nitro'' compou ...

of ''1'' with

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

gives the apical

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

''4'' as an intermediate which is hydrolysed to the apical

''5'' due to the higher steric demand of the active

electrophilic In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carr ...

species. This alcohol can react with

thionyl bromide Thionyl bromide is the chemical compound SOBr2. It is less stable and less widely used than its chloride analogue, thionyl chloride, but engages in similar reactions. Chemistry It is prepared by the action of hydrogen bromide on thionyl chloride ...

to the bromide ''6'' and in a series of steps (not shown) to the corresponding

. Pentamantane can also react with

tetrabromomethane Carbon tetrabromide, CBr4, also known as tetrabromomethane, is a bromide of carbon. Both names are acceptable under IUPAC nomenclature. Production CBr4 can be obtained by the bromination of methane. The byproducts include other brominated methane ...

and tetra-''n''-butylammonium bromide (TBABr) in a

free radical reaction A free-radical reaction is any chemical reaction involving free radicals. This reaction type is abundant in organic reactions. Two pioneering studies into free radical reactions have been the discovery of the triphenylmethyl radical by Moses Gombe ...

to the bromide but without selectivity.

Origin and occurrence

Diamondoids are found in mature high-temperature

fluids (volatile oils, condensates and wet gases). These fluids can have up to a spoonful of diamondoids per US gallon (3.78 liters). A review by Mello and Moldowan in 2005 showed that although the carbon in diamonds is not biological in origin, the diamondoids found in

are composed of carbon from biological sources. This was determined by comparing the ratios of carbon

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

s present.

Optical and electronic properties

The

optical absorption In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy—and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). A ...

for all diamondoids lies deep in the

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

spectral region with optical

band gap In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to t ...

s around 6

electronvolt In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an Voltage, electric potential difference of one volt in vacuum ...

s and higher. The spectrum of each diamondoid is found to reflect its individual size, shape and

symmetry Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is Invariant (mathematics), invariant und ...

. Due to their well-defined size and structure diamondoids also serve as a model system for electronic structure calculations. Many of the optoelectronic properties of diamondoids are determined by the difference in the nature of the highest occupied and lowest unoccupied molecular orbitals: the former is a bulk state, whereas the latter is a

surface state Surface states are electronic states found at the Surface (topology), surface of materials. They are formed due to the sharp transition from solid material that ends with a surface and are found only at the atom layers closest to the surface. The t ...

. As a result, the energy of the lowest unoccupied molecular orbital is roughly independent of the size of the diamondoid. Diamondoids have been found to exhibit a negative

electron affinity The electron affinity (''E''ea) of an atom or molecule is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion. ::X(g) + e− → X−(g) + energy This differs by si ...

, making them potentially useful in electron-emission devices.

References

{{reflist, 30em

External links

Cluster and Nanocrystal Research Group, Technische Universität Berlin

Molecular Diamond Technologies, Chevron Texaco

Electronic and Optical Properties of Diamondoids (free download)

Diamondoid Molecules: With Applications in Biomedicine, Materials Science, Nanotechnology & Petroleum Science

Diamondoid-functionalized gold nanogaps as sensors for natural, mutated, and epigenetically modified DNA nucleotides
Carbon nanoparticles Adamantane-like molecules

Examples

Origin and occurrence

Optical and electronic properties

See also

References

External links