  The diversity of halide materials related to important solar energy systems
such as CsPbX3 (X = Cl, Br, I) is explored by introducing the transition metal
element Fe. In particular a new compound, Cs3Fe2Br9 (space group P6_3/mmc with
a = 7.5427(8) and c = 18.5849(13) {\AA}), has been synthesized and found to
contain 0D face-sharing Fe2Br9 octahedral dimers. Unlike its isomorph,
Cs3Bi2I9, it is black in color, has a low optical bandgap of 1.65 eV and
exhibits antiferromagnetic behavior below TN = 13 K. Density functional theory
calculations shed further light on these properties and also predict that the
material should have anisotropic transport characteristics.
