Tin(II) bromide

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.

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. There is evidence of dimerisation in the gaseous phase. 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. Two polymorphs exist: a room-temperature orthorhombic polymorph, and a high-temperature hexagonal polymorph. Both contain (SnBr₂)_∞ chains but the packing arrangement differs.

Preparation

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

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.<br /> A number of hydrates are known, 2SnBr₂·H₂O, 3SnBr₂·H₂O and 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^&minus; 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 e.g.

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

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.

References