The Color of the Elements: A Combined Experimental and Theoretical Electron Density Study of ScB2 C2.

The chemical or physical control parameters for the onset of superconductivity in MB2 C2 hetero-graphene materials are unclear. This is mainly due to the almost ubiquitous positional B/C disorder, rendering the description of real structures of borocarbides into one of the most challenging problems in materials science. We will show that high-resolution X-ray diffraction data provides all the essential information to decode even complex coloring problems due to B/C disorder. Electron density studies and subsequent analyses of the fine structure of the Laplacian of the electron density resolves the local electronic structure of ScB2 C2 at sub-atomic resolution and allows for an unequivocal identification of all atoms involved in the coloring scenario. This information could finally be used to identify the electron deficient character of the B/C layers in ScB2 C2 and to synthesize the first bimetallic hetero-metallocene with lithium and scandium atoms embedded in the pentagonal and heptagonal voids, respectively.

Can undoped calcium tetraborides exist? An answer from the comparison of its density functional theory electronic structure with that of rare-earth metal tetraboride.

Periodic density functional theory calculations are used to discuss the existence of metal tetraborides MB4 with divalent metals. Tetraborides which contain metal atoms inserted in a three-dimensional boron network made of B6 octahedra and B2 dumbbells exhibit a pseudo energy gap for a count of 60 valence electrons per M4(B6)2(B2)2 formula unit. Such a count satisfies the stability electron requirement for B6(2-) (20 electrons) octahedra and B2(2-) (8 electrons) units and allows the filling of two supplementary low-lying bands deriving from the valence metallic d atomic orbitals. This favored electron count is not reached for CaB4 which is then formally deficient by one electron per metal atom. This indicates that CaB4 is unlikely to exist without n-doping.

Lanthanide Nitrido Borates with Six-Membered B3 N6 Rings: Ln3 B3 N6.

Metal compounds with heteroatomic ring systems of main group elements are a domain of coordination chemistry. However, lanthanide nitrido borates Ln3 B3 N6 (Ln=La or Ce; see structure) are synthesized by the reaction of hexagonal boron nitride with LnN. The compounds contain the six-membered B3 N6 ring, which can be seen as a fragment from one layer of the hexagonal BN structure.

Ca5 Cl3 (C2 )(CBC): A Compound with a Layer Structure and an Unusual Anion Combination.

Allene homologous cumulenes are not always linear! The title compound, which has now been synthesized and structurally characterized, contains a BC2 unit that is isoelectronic with CO2 and that deviates by 16° from linearity without losing the double-bond character of the B-C bonds. The BC2 unit is located in the center of a bicapped trigonal prism of calcium ions (see picture).