Iron(II) bromide refers to inorganic compounds with the chemical formula FeBr2(H2O)x. 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, FeBr2 adopts a polymeric structure consisting of isolated metal centers cross-linked with halides. It crystallizes with the CdI2 structure, featuring close-packed layers of bromide ions, between which are located Fe(II) ions in octahedral holes.[1] The packing of the halides is slightly different from that for FeCl2, which adopts the CdCl2 motif. The tetrahydrates FeX2(H2O)4 (X = Cl, Br) have similar structures, with octahedral metal centers and mutually trans halides.[2]
Synthesis and reactions
FeBr2 is synthesized using a methanol solution of concentrated hydrobromic acid and iron powder. It adds the methanol solvate [Fe(MeOH)6]Br2 together with hydrogen gas. Heating the methanol complex in a vacuum gives pure FeBr2.[3]
FeBr2 reacts with two equivalents of tetraethylammonium bromide to give [(C2H5)4N]2FeBr4.[4] FeBr2 reacts with bromide and bromine to form the intensely colored, mixed-valence species [FeBr3Br9]−.[5]
Magnetism
FeBr2 possesses a strong metamagnetism at 4.2 K and has long been studied as a prototypical metamagnetic compound.[6][7]
