Disilyne is a low valent

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

compound with the chemical formula Si₂R₂ where oxidation state of Si is +1. Several isomers are possible, but none are sufficiently stable to be of practical value.

Substituted Substitution may refer to: Arts and media *Substitution (poetry), a variation in poetic scansion *Substitution (theatre), an acting methodology Music *Chord substitution, swapping one chord for a related one within a chord progression *Tritone ...

disilynes contain a formal silicon–silicon

triple bond A triple bond in chemistry is a chemical bond between two atoms involving six Electron pair bond, bonding electrons instead of the usual two in a covalent bond, covalent single bond. Triple bonds are stronger than the equivalent covalent bond, sin ...

and as such are sometimes written R₂Si₂ (where R is a substituent group). They are the silicon analogues of

alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...

s. The term ''silyne'' has two diverse meanings. Some chemists use it to refer to compounds containing a silicon–silicon triple bond,Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier by analogy to the carbon–carbon triple bond in

s, whereas others use the term to refer to compounds containing a silicon–carbon triple bond by analogy to silene, which often refers to compounds containing silicon–carbon double bonds. The term polysilyne can refer to the layer polymer (SiH)_n or substituted derivatives.

Substituted disilynes

The first substituted disilyne to be isolated and characterised by X-ray crystallography is one with an additional trisubstituted silicon group on each silicon of the disilyne core. The structure , where R′ = HC(SiMe₃)₂ and R′′ = HCMe₂, is an emerald green crystalline compound reported in 2004. It was prepared by the reduction of the related tetrabrominated precursor by

potassium graphite In the area of solid state chemistry, graphite intercalation compounds are a family of materials prepared from graphite. In particular, the sheets of carbon that comprise graphite can be pried apart by the insertion ( intercalation) of ions. Th ...

(KC₈). It is air- and moisture-sensitive but is a stable solid up to 128 °C. The geometry of disilynes is unlike that of analogous carbon structures. Whereas substituted

s, such as 2-butyne, are linear, having a 180°

bond angle 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 deter ...

at each end of the carbon–carbon triple bond, the chain is bent to 137° at each end. The four silicon atoms in the chain are however perfectly coplanar, with the first and fourth silicon atoms ''

trans Trans- is a Latin prefix meaning "across", "beyond", or "on the other side of". Used alone, trans may refer to: Sociology * Trans, a sociological term which may refer to: ** Transgender, people who identify themselves with a gender that di ...

'' to one another. The central triple

bond length In molecular geometry, bond length or bond distance is defined as the average distance between Atomic nucleus, nuclei of two chemical bond, bonded atoms in a molecule. It is a Transferability (chemistry), transferable property of a bond between at ...

is 206 pm, which is around 4% shorter than the typical bond-length of Si–Si double bonds (214 pm)) and the Si–Si single bonds are 237 pm. The color is attributed to a weak π–π^* transition. Calculations show a

bond order In chemistry, bond order is a formal measure of the multiplicity of a covalent bond between two atoms. As introduced by Gerhard Herzberg, building off of work by R. S. Mulliken and Friedrich Hund, bond order is defined as the difference between t ...

of 2.6. An alternative calculation of the bond order by a different group describes the bonding as essentially due to only two electron pairs, with the third pair in a

non-bonding orbital A non-bonding orbital, also known as ''non-bonding molecular orbital'' (NBMO), is a molecular orbital whose occupation by electrons neither increases nor decreases the bond order between the involved atoms. Non-bonding orbitals are often designa ...

. Reaction of this compound with

phenylacetylene Phenylacetylene is an alkyne hydrocarbon containing a phenyl group. It exists as a colorless, viscous liquid. In research, it is sometimes used as an analog for acetylene; being a liquid, it is easier to handle than acetylene gas. Preparation In ...

produced a 1,2-di silabenzene. Other workers have also reported another related compound which contains a hexasila-3-yne chain: :R₃Si(SiR₃)SiMeSi₂SiMe(SiR₃)SiR₃ :where Me = methyl and R = ''t''-butyl In this compound, the Si–Si triple bond length was calculated as 207 pm.

Heavier group 14 analogues

Triple bonded compounds of the heavier members of group 14 have also been prepared;

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

, and

tin Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...

and

germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...

( digermyne) The cores of the disilyne, digermyne, distannyne, and diplumbyne have similarly bent geometries. These findings are generally consistent with the absence of conventional triple bonds.

References

{{Hydrides by group Silicon hydrides

Substituted disilynes

Heavier group 14 analogues

See also

References