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.
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.[1] There is evidence of dimerisation in the gaseous phase.[2] 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.[3] Two polymorphs exist: a room-temperature orthorhombic polymorph, and a high-temperature hexagonal polymorph. Both contain (SnBr2)∞ chains but the packing arrangement differs.
Tin(II) bromide can be prepared by the reaction of metallic tin and HBr distilling off the H2O/HBr and cooling:
Sn + 2 HBr → SnBr2 + H2
However, the reaction will produce tin (IV) bromide in the presence of oxygen.
SnBr2 is soluble in donor solvents such as acetone, pyridine and dimethylsulfoxide to give pyramidal adducts.
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.When dissolved in HBr the pyramidal SnBr3- ion is formed.Like SnCl2 it is a reducing agent. With a variety of alkyl bromides oxidative addition can occur to yield the alkyltin tribromide[4] 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[5] 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.[6]