Nickel(II) bromide is the name for the

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

s with the chemical formula NiBr₂(H₂O)_''x''. The value of ''x'' can be 0 for the anhydrous material, as well as 2, 3, or 6 for the three known

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

forms. The anhydrous material is a yellow-brown solid which dissolves in

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

to give blue-green hexahydrate (see picture).

Structure

The structure of the nickel bromides varies with the degree of hydration. In all of these cases, the nickel(II) ion adopts an

octahedral molecular geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The o ...

. Similar structures are observed in aqueous solutions of nickel bromide. *Anhydrous NiBr₂ adopts the hexagonal

cadmium chloride Cadmium chloride is a white crystalline compound of cadmium and chloride, with the formula CdCl2. This salt is a hygroscopic solid that is highly soluble in water and slightly soluble in alcohol. The crystal structure of cadmium chloride (describe ...

structure. The interatomic distance for Ni-Br is 2.52—2.58 Å. Anhydrous NiBr₂ is a

paramagnet Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...

at room temperature. Upon cooling, it turns into an

antiferromagnet In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. ...

at 52 K, and then into a helimagnet at 22.8 K. *The structure of the trihydrate has not been confirmed by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

. It is assumed to adopt a chain structure. *The di- and hexahydrates adopt structures akin to those for the corresponding chlorides. The dihydrate consists of a linear chain, whereas the hexahydrate features isolated ''trans''- iBr₂(H₂O)₄molecules together with two water molecules of crystallization.

Reactions and uses

NiBr₂ has

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...

character, as indicated by its tendency to hydrate and form adducts with a variety of other Lewis bases. NiBr₂ is also used to prepare catalysts for

cross-coupling reaction In organic chemistry, a cross-coupling reaction is a reaction where two different fragments are joined. Cross-couplings are a subset of the more general coupling reactions. Often cross-coupling reactions require metal catalysts. One important re ...

s and various

carbonylation In chemistry, carbonylation refers to reactions that introduce carbon monoxide (CO) into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemis ...

s. NiBr₂-glyme shows increased activity compared to NiCl₂-glyme for some transformations.

Structure

Reactions and uses

Safety

References

Cited sources