Nickel(II) bromide is the name for theinorganic compounds with the chemical formula NiBr2(H2O)x. The value ofx can be 0 for the anhydrous material, as well as 2, 3, or 6 for the three knownhydrate forms. The anhydrous material is a yellow-brown solid which dissolves inwater to give blue-green hexahydrate (see picture).
The structure of the nickel bromides varies with the degree of hydration. In all of these cases, the nickel(II) ion adopts anoctahedral molecular geometry. Similar structures are observed in aqueous solutions of nickel bromide.[7]
Anhydrous NiBr2 adopts the hexagonalcadmium chloride structure.[8] The interatomic distance for Ni-Br is 2.52—2.58 Å.[7] Anhydrous NiBr2 is aparamagnet at room temperature. Upon cooling, it turns into anantiferromagnet at 52 K, and then into a helimagnet at 22.8 K.[5]
The structure of the trihydrate has not been confirmed byX-ray crystallography. It is assumed to adopt a chain structure.[9]
The di- and hexahydrates adopt structures akin to those for the corresponding chlorides. The dihydrate consists of a linear chain, whereas the hexahydrate features isolatedtrans-[NiBr2(H2O)4] molecules together with two water molecules of crystallization.
NiBr2 hasLewis acid 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 forcross-coupling reactions and variouscarbonylations.[8] NiBr2-glyme shows increased activity compared to NiCl2-glyme for some transformations.[10]
^Defotis, G. C.; Goodey, J. R.; Narducci, A. A.; Welch, M. H. (1996). "NiBr2·3H2O, a lower dimensional antiferromagnet".Journal of Applied Physics.79 (8): 4718.doi:10.1063/1.361651.
