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Polythiazyl ( polymeric
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
nitride), , is an
electrically conductive Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
, gold- or bronze-colored polymer with metallic luster. It was the first conductive inorganic polymer discovered and was also found to be a superconductor at very low temperatures (below 0.26 K). It is a fibrous solid, described as "lustrous golden on the faces and dark blue-black", depending on the orientation of the sample. It is air stable and insoluble in all solvents.


History

The compound was first reported as early as 1910 by F.P. Burt, who obtained it by heating tetrasulfur tetranitride in vacuum over silver wool. The compound was the first non-metallic compound in which
superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...
could be demonstrated. However, the relatively low
transition temperature Transition temperature is the temperature at which a material changes from one crystal state (allotrope) to another. More formally, it is the temperature at which two crystalline forms of a substance can co-exist in equilibrium. For example, when ...
at about 0.3 K makes a practical application unlikely.Alsfasser, R.; Janiak, C.; Klapötke, T.M.; Meyer, H.-J.: ''Moderne Anorganische Chemie'', Herausgeber Riedel, E., 3. Auflage 2007, Walter de Gruyter GmbH & Co. KG, Berlin/Boston, , S. 129–132, (retrieved via De Gruyter Online).


Properties

Polythiazyl is a metallic-golden and shiny, crystalline but fibrous material. The polymer is mostly inert to oxygen and water, but decomposes in air to a grey powder. At temperatures above 240 °C explosive decomposition can occur. Wiberg, E.; Wiberg, N.; Holleman, A.F.: '' Anorganische Chemie'', 103. Auflage, 2017 Walter de Gruyter GmbH & Co. KG, Berlin/Boston, , S. 681, (retrieved via De Gruyter Online). The compound also explodes on impact. Polythiazyl shows an anisotropic electrical conductivity. Along the fibres or SN chains, the bond is electrically conductive, perpendicular to it acts as an insulator. The one-dimensional conductivity is based on the bonding conditions in the S-N chain, where each sulfur atom provides two π electrons and each nitrogen atom provides one π electron to form two-center 3π electron bonding units. Two polymorphic crystal forms were observed in the compound. The monoclinic form I obtained from the synthesis can be converted into an orthorhombic form II by mechanical treatment such as grinding.Baughman, R.H.; Apgar, P.A.; Chance, R.R.; MacDiarmid, A.G.; Garito, A.F.: ''A New Phase of (SN)x'' in
J. Chem. Soc. The ''Journal of the Chemical Society'' was a scientific journal established by the Chemical Society in 1849 as the ''Quarterly Journal of the Chemical Society''. The first editor was Edmund Ronalds. The journal underwent several renamings, splits ...
Chem. Comm. 1977, 49–50, .


Structure and bonding

The material is a polymer, containing trivalent nitrogen, and divalent and tetravalent sulfur. The S and N atoms on adjacent chains align. Several resonance structures can be written. : The structure of the crystalline compound was resolved by
X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. This showed alternating S–N bond lengths of 159 pm and 163 pm and S–N–S bond angles of 120 ° and N–S–N bond angles of 106 °.MacDiarmid, A.G.; Mikulski, C.M.; Russo, P.J.; Saran, M.S.; Garito, A.F.; Heeger, A.J.: ''Synthesis and structure of the polymeric metal, (SN)x, and its precursor, S2N2'' in
J. Chem. Soc. The ''Journal of the Chemical Society'' was a scientific journal established by the Chemical Society in 1849 as the ''Quarterly Journal of the Chemical Society''. The first editor was Edmund Ronalds. The journal underwent several renamings, splits ...
Chem. Comm. 1975, 476–477, .
MacDiarmid, A.G.; Mikulski, C.M.; Saran, M.S.; Russo, P.J.; Cohen, M.J.; Bright, A.A.; Garito, A.F.; Heeger, A.J.: ''Synthesis and Selected Properties of Polymeric Sulfur Nitride, (Polythiazyl), (SN)x'' in
Advances in Chemistry This is a list of academic journals published by Hindawi. A B C D E G H I J L M N O P Q R S T U V W References {{Reflist External linksList of journals published by Hindawi * Hindawi Hindawi or H ...
150 (2009) 63–72, .


Synthesis

Polythiazyl is synthesized by the polymerization of the dimer disulfur dinitride (), which is in turn synthesized from the cyclic alternating tetramer tetrasulfur tetranitride (). Conversion from cyclic tetramer to
dimer Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ( ...
is catalysed with hot silver wool. : :S4N4 (w/ Ag2S catalyst) → 2 S2N2 (w/ 77K cold finger) → S2N2 :S2N2 (@ 0°C, sublimes to surface) → thermal polymerization → (SN)x


Uses

Due to its electrical conductivity, polythiazyl is used in
LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s, transistors, battery cathodes, and solar cells.


Literature

King, R.S.P.: ''Novel chemistry and applications of polythiazyl'', Doctoral Thesis Loughborough University 2009
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References

{{reflist Inorganic polymers Nitrides Superconductors Sulfur–nitrogen compounds Conductive polymers