Tin(II) oxide

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IUPACName = tin(II) oxide
OtherNames = stannous oxide
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CASNo = 21651-19-4
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Formula = SnO
MolarMass = 134.709
Appearance = black powder
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MeltingPt = 1080 °C [Tin and Inorganic Tin Compounds: Concise International Chemical Assessment Document 65, (2005), World Health Organization]
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Tin(II) oxide (stannous oxide) is a compound of tin and oxygen where tin has the oxidation state of +2. There are two forms, a stable blue-black form and a metastable red form.

Preparation and reactions

Blue-black SnO can be prepared by heating the tin(II) oxide hydrate, SnO.xH₂O (x<1) precipitated when a tin(II) salt is reacted with an alkali hydroxide such as NaOH.Egon Wiberg, Arnold Frederick Holleman (2001) "Inorganic Chemistry", Elsevier ISBN 0123526515] Metastable, red SnO can be prepared by gentle heating of the precipitate produced by the action of aqueous ammonia on a tin(II) salt.SnO may be prepared as a pure substance in the laboratory, by controlled heating of tin(II) oxalate (stannous oxalate) in the absence of air. [Satya Prakash (2000),"Advanced Inorganic Chemistry: V. 1", S. Chand, ISBN 8121902630] :SnC₂O₄ → SnO + CO₂ + CO

Tin(II) oxide burns in air to form SnO₂.When heated in an inert atmosphere initially disproportionation occurs giving Sn metal and Sn₃O₄ which further reacts to give SnO₂ and Sn metal.:4SnO → Sn₃O₄ + Sn:Sn₃O₄ → 2SnO₂ + SnSnO is amphoteric dissolving in strong acid to give tin(II) salts and in strong base to give stannites containing Sn(OH)³⁻. In acid solutions ionic complexes Sn(OH₂)₃²⁺ and Sn(OH)(OH₂)⁺, in less acid solutions and Sn₃(OH)₄⁺. Note that anhydrous stannites, e.g. K₂Sn₂O₃, K₂SnO₂ are also known. [The First Oxostannate(II): K₂Sn₂O₃, M Braun, R. Hoppe, Angewandte Chemie International Edition in English, 17, 6, 449 - 450, doi|10.1002/anie.197804491 ] [Über Oxostannate(II). III. K₂Sn₂O₃, Rb₂Sn₂O₃ und Cs₂Sn₂O₃ - ein Vergleich, R. M. Braun, R. Hoppe, Zeitschrift für anorganische und allgemeine Chemie, 485, 1, 15 - 22, doi|10.1002/zaac.19824850103] [ R M Braun R Hoppe Z. Naturforsch. (1982), 37B, 688-694] SnO is a reducing agent and this appears to its role in the manufacture of so-called "copper ruby glass". [Colour development in copper ruby alkali silicate glasses. Part I: The impact of tin oxide, time and temperature ,Bring, T., Jonson, B., Kloo, L. Rosdahl, J , Wallenberg, R., Glass Technology, Eur. J. Glass Science & Technology, Part A, 48 , 2 , 101-108 ( 2007)]

tructure

Black, α-SnO adopts the tetragonal PbO layer structure containing four coordinate square pyramidal tin atoms. [ Wells A.F. (1984) "Structural Inorganic Chemistry" 5th edition Oxford Science Publications ISBN 0-19-855370-6 ] . This form is found in nature as the rare mineral romarchite. [On type romarchite and hydroromarchite from Boundary Falls, Ontario, and notes on other occurrences, Robert A. Ramik,, Robert M. Organ, Joseph A. Mandarino, The Canadian Mineralogist; June 2003; v. 41; no. 3;. 649-657; doi|10.2113/gscanmin.41.3.649] The asymmetry is usually simply ascribed to a sterically active lone pair, however electron density calculations show that the asymmetry is caused by an antibonding interaction of the Sn(5s) and the O(2p) orbitals. [Electronic structures of rocksalt, litharge, and herzenbergite SnO by density functional theory, A. Walsh, G.W. Watson, Phys. Rev. B 70, 235114 (2004)doi|10.1103/PhysRevB.70.235114} ]
Non-stoichiometry has been observed in SnO. [Cation nonstoichiometry in tin-monoxide-phase Sn_1-δO with tweed microstructure, Moreno, M. S.; Varela, A.; Otero-Díaz, L. C., Physical Review B (Condensed Matter),56, 9,(1997), 5186-5192, doi|10.1103/PhysRevB.56.5186]

The electronic band gap has been measured between 2.5eV and 3eV. [Science and Technology of Chemiresistor Gas Sensors By Dinesh K. Aswal, Shiv K. Gupta (2006), Nova Publishers, ISBN 1600215149]

Uses

The dominant use of stannous oxide is as a precursor in manufacturing of other, typically divalent, tin compounds or salts. Stannous oxide may also be employed as a reducing agent and in the creation of ruby glass. It has a minor use as an esterification catalyst.

References