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A cubane-type cluster is an arrangement of atoms in a 
Other compounds in the class have different elements in the corners, and various atoms or groups bonded to the corners.
Most cubanes have more complicated structures, usually with nonequivalent vertices. They may be simple covalent compounds or
DasCubane.png, Das cubane, oO(OAc)pysub>4 (OAc =
A cubane-type cluster is an arrangement of atoms in a molecular structure
Molecular geometry is the three-dimensional arrangement of the atoms that constitute a molecule. It includes the general shape of the molecule as well as bond lengths, bond angles, torsional angles and any other geometrical parameters that det ...
that forms a cube
A cube or regular hexahedron is a three-dimensional space, three-dimensional solid object in geometry, which is bounded by six congruent square (geometry), square faces, a type of polyhedron. It has twelve congruent edges and eight vertices. It i ...
. In the simplest case, the eight vertices are symmetry equivalent and the species has Oh 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 ...
. Such structure occurs in the hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
cubane
Cubane is a synthetic hydrocarbon compound with the Chemical formula, formula . It consists of eight carbon atoms arranged at the corners of a Cube (geometry), cube, with one hydrogen atom attached to each carbon atom. A solid crystalline substanc ...
(chemical formula
A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...
), which has carbon atoms at the corners of a cube and covalent bond
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...
s forming the edges.
:
Other compounds in the class have different elements in the corners, and various atoms or groups bonded to the corners.
Most cubanes have more complicated structures, usually with nonequivalent vertices. They may be simple covalent compounds or macromolecular
A macromolecule is a "molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass." Polymers are physi ...
or supramolecular cluster compound
Nanoclusters are atomically precise, crystalline materials most often existing on the 0-2 nanometer scale. They are often considered kinetically stable intermediates that form during the synthesis of comparatively larger materials such as semic ...
s.
Examples
Heavieradamantogen
The carbon group is a periodic table group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl). It lies within the p-block.
In modern IUPAC notation, it is called group 14. In the field of semico ...
cubanes with all vertices identical are all known, and exhibit only about half as much strain energy
In physics, the elastic potential energy gained by a wire during elongation with a tensile (stretching) or compressive (contractile) force is called strain energy. For linearly elastic materials, strain energy is:
: U = \frac 1 2 V \sigma \v ...
as cubane per molecule. The inert pair effect
The inert-pair effect is the tendency of the two electrons in the outermost atomic ''s''-orbital to remain unshared in compounds of post-transition metals. The term ''inert-pair effect'' is often used in relation to the increasing stability of o ...
is believed to drive stability in cubanes with heavy main group
In chemistry and atomic physics, the main group is the group of elements (sometimes called the representative elements) whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arran ...
elements: the bonding orbital
In theoretical chemistry, the bonding orbital is used in molecular orbital (MO) theory to describe the attractive interactions between the atomic orbitals of two or more atoms in a molecule. In MO theory, electrons are portrayed to move in waves. ...
s are almost entirely unhybridized ''p'' orbitals, and so naturally adopt 90° angles at the vertices.
Simple inorganic cubane-type clusters include selenium tetrachloride
Selenium tetrachloride is the inorganic compound composed with the formula SeCl4. This compound exists as yellow to white volatile solid. It is one of two commonly available selenium chlorides, the other example being selenium monochloride, Se2 ...
, tellurium tetrachloride
Tellurium tetrachloride is the inorganic compound with the empirical formula TeCl4. The compound is volatile, subliming at 200 °C at 0.1 mmHg. Molten TeCl4 is ionic, dissociating into TeCl3+ and Te2Cl102−.
Structure
TeCl4 is mono ...
, and sodium silox.
Many alkyllithium
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...
compounds, including methyl- and ''tert''-butyllithium, exist as tetramer
A tetramer () (''tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula ...
ic clusters in solution. The four lithium atoms and the carbon from each alkyl group bonded to them occupy alternating vertices of the cube, with the additional atoms of the alkyl groups projecting off their respective corners.
Cubane clusters are common throughout bioinorganic chemistry
Bioinorganic chemistry is a field that examines the role of metals in biology. Bioinorganic chemistry includes the study of both natural phenomena such as the behavior of metalloproteins as well as artificially introduced metals, including those t ...
. Ferredoxin
Ferredoxins (from Latin ''ferrum'': iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied t ...
s containing e4S4iron–sulfur cluster
Iron–sulfur clusters are molecular ensembles of iron and sulfide. They are most often discussed in the context of the biological role for iron–sulfur proteins, which are pervasive. Many Fe–S clusters are known in the area of organometall ...
s are pervasive in nature. The four iron atoms and four sulfur atoms form an alternating arrangement at the corners. The whole cluster is typically anchored by coordination of the iron atoms, usually with cysteine
Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...
residues. In this way, each Fe center achieves tetrahedral coordination geometry
In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are arccos(−) = 109.4712206...° ≈ 109.5° when all four substituents are ...
. Some e4S4clusters arise via dimerization of square-shaped e2S2precursors. Many synthetic analogues are known including heterometallic derivatives.
acetate
An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic, or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...
; py = pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...
)
Fe4S4.svg, Ferredoxin (4Fe-4S-cubane)
Oxygen Evolving Complex Crystal structure to 1.9 Angstrom Resolution.png, CaMn3O4 cubane in Photosystem II
Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem ...
.
Octaazacubane
Octaazacubane is a hypothetical explosive allotrope of nitrogen with formula N8, whose molecules have eight atoms arranged into a cube. (By comparison, nitrogen usually occurs as the diatomic molecule N2.) It can be regarded as a cubane-type clu ...
is a hypothetical allotrope
Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...
of nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
with formula N8; the nitrogen atoms are the corners of the cube. Like the carbon-based cubane compounds, octaazacubane is predicted to be highly unstable due to angle strain
In organic chemistry, ring strain is a type of instability that exists when bonds in a molecule form angles that are abnormal. Strain is most commonly discussed for small rings such as cyclopropanes and cyclobutanes, whose internal angles are su ...
at the corners, and it also does not enjoy the kinetic stability
In chemistry and physics, metastability is an intermediate energetic state within a dynamical system other than the system's state of least energy.
A ball resting in a hollow on a slope is a simple example of metastability. If the ball is onl ...
seen for its organic analogues.
References
{{Reflist Molecular geometry