Tin(II) bromide

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Tin(II) bromide
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Template:Longitem SnBr2
Molar mass 278.518 g/mol
Appearance yellow powder
Density 5.12 g/cm3, solid
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Template:Longitem related to PbCl2

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Tin(II) bromide is a chemical compound of tin and bromine with a chemical formula of SnBr2. Tin is in the +2 oxidation state. The stability of tin compounds in this oxidation state is attributed to the inert pair effect.[1]

Structure and bonding

In the gas phase SnBr2 is non-linear with a bent configuration similar to SnCl2 in the gas phase. The Br-Sn-Br angle is 95° and the Sn-Br bond length is 255pm.[2] There is evidence of dimerisation in the gaseous phase.[3] The solid state structure is related to that of SnCl2 and PbCl2 and the tin atoms have five near bromine atom neighbours in an approximately trigonal bipyramidal configuration.[4] Two polymorphs exist: a room-temperature orthorhombic polymorph, and a high-temperature hexagonal polymorph. Both contain (SnBr2) chains but the packing arrangement differs.[5]

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Preparation

Tin(II) bromide can be prepared by the reaction of metallic tin and HBr distilling off the H2O/HBr and cooling:[6]

Sn + 2 HBr → SnBr2 + H2

However, the reaction will produce tin (IV) bromide in the presence of oxygen.

Reactions

SnBr2 is soluble in donor solvents such as acetone, pyridine and dimethylsulfoxide to give pyramidal adducts.[6]
A number of hydrates are known, 2SnBr2·H2O, 3SnBr2·H2O & 6SnBr2·5H2O which in the solid phase have tin coordinated by a distorted trigonal prism of 6 bromine atoms with Br or H2O capping 1 or 2 faces.[1] When dissolved in HBr the pyramidal SnBr3 ion is formed.[1] Like SnCl2 it is a reducing agent. With a variety of alkyl bromides oxidative addition can occur to yield the alkyltin tribromide[7] e.g.

SnBr2 + RBr → RSnBr3

Tin(II) bromide can act as a Lewis acid forming adducts with donor molecules e.g. trimethylamine where it forms NMe3·SnBr2 and 2NMe3·SnBr2 [8] It can also act as both donor and acceptor in, for example, the complex F3B·SnBr2·NMe3 where it is a donor to boron trifluoride and an acceptor to trimethylamine.[9]

References

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  2. J.L Wardell "Tin:Inorganic Chemistry" Encyclopedia of Inorganic Chemistry Ed: R Bruce King John Wiley & Sons (1994) Template:ISBN
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