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Silanes Silanes refers to diverse kinds of charge-neutral silicon compounds with the formula . The R substituents can any combination of organic or inorganic groups. Most silanes contain Si-C bonds, and are discussed under organosilicon compounds. Examp ...
are
saturated Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds ** Saturated and unsaturated compounds **Degree of unsaturation ** Saturated fat or fatty ac ...
chemical compounds with the empirical formula SixHy. They are hydrosilanes, a class of compounds that includes compounds with Si-H and other Si-X bonds. All contain
tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
silicon and terminal hydrides. They only have Si–H and Si–Si single bonds. The
bond length In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...
s are 146.0 pm for a Si–H bond and 233 pm for a Si–Si bond. The structures of the silanes are analogues of the alkanes, starting with
silane Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...
, , the analogue of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
, continuing with
disilane Disilane is a chemical compound with chemical formula Si2H6 that was identified in 1902 by Henri Moissan and Samuel Smiles (1877–1953). Moissan and Smiles reported disilane as being among the products formed by the action of dilute acids on meta ...
, the analogue of
ethane Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
, etc. They are mainly of theoretical or academic interest.


Inventory

132px, Cyclopentasilane_is_structurally_similar_to_cyclopentane,_just_larger..html" ;"title="cyclopentane.html" ;"title="Cyclopentasilane is structurally similar to cyclopentane">Cyclopentasilane is structurally similar to cyclopentane, just larger.">cyclopentane.html" ;"title="Cyclopentasilane is structurally similar to cyclopentane">Cyclopentasilane is structurally similar to cyclopentane, just larger. The simplest isomer of a silane is the one in which the silicon atoms are arranged in a single chain with no branches. This isomer is sometimes called the ''n''-isomer (''n'' for "normal", although it is not necessarily the most common). However the chain of silicon atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of silicon atoms. The members of the series (in terms of number of silicon atoms) follow: :
silane Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...
, - one silicon and four hydrogen :
disilane Disilane is a chemical compound with chemical formula Si2H6 that was identified in 1902 by Henri Moissan and Samuel Smiles (1877–1953). Moissan and Smiles reported disilane as being among the products formed by the action of dilute acids on meta ...
, - two silicon and six hydrogen, ethane-like structure :trisilane, - three silicon and 8 hydrogen, propane-like structure :tetrasilane, - four silicon and 10 hydrogen (one isomer: isotetrasilane, analogous to butane and isobutane) :pentasilane, - five silicon and 12 hydrogen (two isomers: isopentasilane and neopentasilane) Silanes are named by adding the suffix -silane to the appropriate numerical multiplier prefix. Hence, disilane, ; trisilane ; tetrasilane ; pentasilane ; etc. The prefix is generally Greek, with the exceptions of nonasilane which has a
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
prefix, and undecasilane and tridecasilane which have mixed-language prefixes. Solid phase polymeric silicon hydrides called polysilicon hydrides are also known. When hydrogen in a linear polysilene polysilicon hydride is replaced with
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
or
aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromaticity, aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar ...
side-groups, the term polysilane is used. 3-Silylhexasilane, H3SiSiH2SiH(SiH3)SiH2SiH2SiH3, is the simplest chiral binary noncyclic silicon hydride. Cyclosilanes also exist. They are structurally analogous to the cycloalkanes, with the formula Si''n''H2''n'', ''n'' > 2.


Production

Early work was conducted by
Alfred Stock Alfred Stock (July 16, 1876 – August 12, 1946) was a German inorganic chemist. He did pioneering research on the hydrides of boron and silicon, coordination chemistry, mercury, and mercury poisoning. The German Chemical Society's Alfred-Stoc ...
and Carl Somiesky. Although monosilane and disilane were already known, Stock and Somiesky discovered, beginning in 1916, the next four members of the SinH2n+2 series, up to n = 6. They also documented the formation of solid phase polymeric silicon hydrides. One of their synthesis methods involved the hydrolysis of metal
silicide A silicide is a type of chemical compound that combines silicon and a (usually) more electropositive element. Silicon is more electropositive than carbon. Silicides are structurally closer to borides than to carbides. Similar to borides and carb ...
s. This method produces a mixture of silanes, which required separation on a high vacuum line. The silanes (SinH2n+2) are less thermally stable than
alkanes In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...
(CnH2n+2). They tend to undergo
dehydrogenation In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At ...
, yielding hydrogen and polysilanes. For this reason, the isolation of silanes higher than heptasilane has proved difficult.W. W. Porterfield "Inorganic Chemistry: A Unified Approach," Academic Press (1993) p. 219. The Schlesinger process is used to prepare silanes by the reaction of per
chlorosilane Chlorosilanes are a group of reactive, chlorine-containing chemical compounds, related to silane and used in many chemical processes. Each such chemical has at least one silicon-chlorine bond. Trichlorosilane is produced on the largest scale. The p ...
s with lithium aluminium hydride.


Applications

The single but significant application for SiH4 is in the
microelectronics Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre-s ...
industry. By metal organic chemical vapor deposition, silane is converted to silicon by thermal decomposition: :SiH4 → Si + 2 H2


Hazards

Silane is explosive when mixed with air (1 – 98% SiH4). Other lower silanes can also form explosive mixtures with air. The lighter liquid silanes are highly flammable; this risk increases with the length of the silicon chain. Considerations for detection/risk control: *Silane is slightly denser than air (possibility of pooling at ground levels/pits) *Disilane is denser than air (possibility of pooling at ground levels/pits) *Trisilane is denser than air (possibility of pooling at ground levels/pits)


Nomenclature

The IUPAC nomenclature (systematic way of naming compounds) for silanes is based on identifying hydrosilicon chains. Unbranched, saturated hydrosilicon chains are named systematically with a Greek numerical prefix denoting the number of silicons and the suffix "-silane". IUPAC naming conventions can be used to produce a systematic name. The key steps in the naming of more complicated branched silanes are as follows: *Identify the longest continuous chain of silicon atoms *Name this longest root chain using standard naming rules *Name each side chain by changing the suffix of the name of the silane from "-ane" to "-anyl", except for "silane" which becomes "silyl" *Number the root chain so that the sum of the numbers assigned to each side group will be as low as possible *Number and name the side chains before the name of the root chain The nomenclature parallels that of
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
radicals. Silanes can also be named like any other inorganic compound; in this naming system, silane is named ''silicon tetrahydride''. However, with longer silanes, this becomes cumbersome.


See also

* Organosilicon compounds, compounds containing carbon–silicon bonds * Hydrosilanes, a larger class of compounds with the formula HmSiRn (m ≠ 0)


References

{{Hydrides by group * pl:Krzemowodory