Cyclopentasilane is a cyclic compound of silicon and hydrogen. Containing five silicon atoms arranged in a ring, it is the silicon analog of
cyclopentane
Cyclopentane (also called C pentane) is a highly flammable alicyclic hydrocarbon with chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occu ...
. Cyclopentasilane is a liquid 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 (C
6H
5)
2SiCl
2 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.
[
]
Properties
Cyclopentasilane is pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , '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 organolit ...
. 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 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 ...
.
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 D5h; envelope symmetry Cs, 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