Lead Carbodiimides Related to the Mineral Bideauxite

The luminescent semiconductor Pb7I6(CN2)4

The development of new compounds in the domain of metal dinitridocarbonates is most efficiently performed via solid-state metathesis or simply by addition reactions. Our discovery of Pb7I6(CN2)4 is the result of a solid-state reaction of PbCN2 with PbI2 at 420 °C. Its crystal structure was solved and refined from X-ray diffraction data based on a single crystal with the space group P63/mmc. The crystal structure is based on a network of lead tetrahedra, lead trigonal bipyramids and lead octahedra interconnected by [NCN]2- and iodide. Properties of the material were investigated by diffuse reflection measurement, photoluminescence measurements, and electronic band structure calculations demonstrating that this material is a semiconductor.

PbCN2 – an elucidation of its modifications and morphologies

Concerning the crystal structure of PbCN2 there exist two different descriptions in the literature, one based on the non-centrosymmetric structure, space group Pna21, another one on the centrosymmetric one in space group Pnma. To elucidate the conditions for their appearance, comprehensive preparative and structural investigations have been conducted which proved the existence of two distinct modifications of PbCN2. A detailed comparison of the two phases is provided. The growth conditions and crystallization processes of the two PbCN2 structures are reported with focus on the influence of the pH value on the products. Depending on the growth conditions several different morphologies arise, namely PbCN2 in needle-shaped and platelet-shaped crystals, as well as pompon-shaped and lance-shaped crystals.

Synthesis, Structure, and Electronic Properties of Sn(CN2) and Sn4Cl2(CN2)3

A solid-state metathesis reaction between equimolar amounts of Li₂(CN₂) and SnCl₂ revealed the formation of two new compounds, Sn₄Cl₂(CN₂)₃ and Sn(CN₂). Thermal analysis of this reaction indicated that Sn₄Cl₂(CN₂)₃ forms exothermically near 200 °C and subsequently transforms into Sn(CN₂) at higher temperatures. The crystal structures of both compounds are presented. According to optical measurements and band structure calculations, Sn(CN₂) can be considered as a semiconductor with a band gap on the order of 2 eV. The presence of Sn²⁺ ions in the structure of Sn(CN₂) with a toroidally shaped lone pair is indicated by electron localization function calculations. The structure of Sn(CN₂) is shown to be related to the structures of FeS₂ and CaC₂.