Synthesis, Structure, and Tunability of Zero-Dimensional Organic–Inorganic Metal Halides Utilizing the m-Xylylenediammonium Cation: MXD(2)PbI(6), MXDBiI(5), and MXD(3)Bi(2)Br(12)·2H(2)O

[Image: see text] Over the past decade, the efficiency of photovoltaic devices based on CH(3)NH(3)PbI(3) have dramatically increased. This has driven research efforts in all areas, from the discovery of materials to film processing to long-term device stability studies. Here, we report the synthesis and structure of three new “zero dimensional” organic–inorganic metal halides which use the meta-xylylenediammonium (MXD) cation: MXD(2)PbI(6), MXDBiI(5), and (MXD)(3)Bi(2)Br(12)·2H(2)O. The different structures of the new materials lead to compounds with a range of band gaps with MXDBiI(5) having the lowest at 2.15 eV. We have explored the tunabilty of MXDBiI(5) through halide substitution by preparing a series of samples with composition MXDBiI(5–x)Br(x) and determined the halide content using energy dispersive X-ray spectroscopy. A large range of solid solution is obtained in MXDBiI(5–x)Br(x), resulting in the formation of single-phase materials for bromine contents from x = 0 to 3.71 (iodine contents from 1.29 to 5). This highlights the fact that zero-dimensional organic–inorganic halides are highly tunable, in a similar manner to the higher-dimensional perovskite counterparts. Such new materials open up the opportunity for further studies of the physics and optoelectronic properties of these materials.