Cyclopentasilane is a cyclic compound of

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 ...

and

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

with the

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 ...

. Containing five silicon atoms arranged in a

pentagonal In geometry, a pentagon () is any five-sided polygon or 5-gon. The sum of the internal angles in a simple pentagon is 540°. A pentagon may be simple or self-intersecting. A self-intersecting ''regular pentagon'' (or ''star pentagon'') is cal ...

ring, it is the silicon analog of

cyclopentane Cyclopentane (also called C pentane) is a highly flammable alicyclic compound, alicyclic hydrocarbon with chemical formula C5H10, C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and ...

. Cyclopentasilane is a colorless

pyrophoric A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...

liquid. It is an oligosilane. It is of research interest because of its potential use as a liquid silicon ink for printing silicon structures on integrated circuits or solar cells.

Production

Cyclopentasilane can be made from diphenyldichlorosilane (C₆H₅)₂SiCl₂ reacting with lithium. This forms decaphenylcyclopentasilane. This reacts with aluminium chloride in benzene catalysed with hydrogen chloride to yield decachlorocyclopentasilane. Decachlorocyclopentasilane then has its chlorine replaced by hydrogen using

lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula or . It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthe ...

Properties

Cyclopentasilane is

. It has a σ-delocalization property. Cyclopentasilane is a liquid at standard conditions, but can be frozen to crystals at 173K. The monoclinic crystals are not isomorphic to cyclopentane. The silicon to silicon bond lengths in the solid vary from 2.3353 and 2.3377 Å, which is shorter than in the substituted cyclopentasilanes or linear silanes. In gas form, those bond lengths, as measured by electron diffraction, increased to 2.342 Å. Cyclopentasilane is sensitive, and starts decomposing when heated over 84°C, when it loses hydrogen and polymerizes. As it is heated more silane is produced, and at 178°C it yields

disilane Disilane is a chemical compound with general chemical formula Si2R6 that was first identified in 1902 by Henri Moissan and Samuel Smiles (1877–1953) where R = H. Moissan and Smiles reported disilane as being among the products formed by the actio ...

. When heated to over 250°C it decomposes to a silicon hydrogen polymer.

Molecule shape

A five member ring can adopt a number of shapes: planar with all the atoms arranged in a pentagon with symmetry D_5h; envelope symmetry C_s, with four atoms in a rectangular plane and one popped up like the flap, and twist with symmetry C₂. The planar form has slightly higher energy than the other forms.

References

{{Reflist Silanes Five-membered rings