Iron(II) bromide refers to inorganic compounds with the chemical formula FeBr<sub>2</sub>(H<sub>2</sub>O)<sub>x</sub>. The anhydrous compound (x = 0) is a yellow or brownish-colored paramagnetic solid. The tetrahydrate is also known, all being pale colored solids. They are common precursor to other iron compounds.
Like most metal halides, FeBr<sub>2</sub> adopts a polymeric structure consisting of isolated metal centers cross-linked with halides. It crystallizes with the CdI<sub>2</sub> structure, featuring close-packed layers of bromide ions, between which are located Fe(II) ions in octahedral holes. The packing of the halides is slightly different from that for FeCl<sub>2</sub>, which adopts the CdCl<sub>2</sub> motif. The tetrahydrates FeX<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub> (X = Cl, Br) have similar structures, with octahedral metal centers and mutually trans halides.
FeBr<sub>2</sub> is synthesized using a methanol solution of concentrated hydrobromic acid and iron powder. It adds the methanol solvate [Fe(MeOH)<sub>6</sub>]Br<sub>2</sub> together with hydrogen gas. Heating the methanol complex in a vacuum gives pure FeBr<sub>2</sub>.
FeBr<sub>2</sub> reacts with two equivalents of tetraethylammonium bromide to give [(C<sub>2</sub>H<sub>5</sub>)<sub>4</sub>N]<sub>2</sub>FeBr<sub>4</sub>. FeBr<sub>2</sub> reacts with bromide and bromine to form the intensely colored, mixed-valence species [FeBr<sub>3</sub>Br<sub>9</sub>]<sup>âÂÂ</sup>.
FeBr<sub>2</sub> possesses a strong metamagnetism at 4.2 K and has long been studied as a prototypical metamagnetic compound.