Bis(1-adamantylammonium) hexafluoridogermanate

The title compound, (C10H18N)2[GeF6], was obtained hydro­thermally from an aqueous solution of GeO2, H3BO3, NiCl2, adamantylammonium chloride, butanol and hydro­fluoric acid. The structure consists of discrete bis(1-adamantylammonium) cations lying on crystallographic mirror planes and hexa­fluoridogermanate anions disordered about sites of 2/m point symmetry. In the latter, the Ge atom lies on the site of 2/m symmetry, one F atom lies on the mirror plane and two further F atoms are included in general positions with 50% site occupancy. The cations and anions lie in layers with N—H⋯F hydrogen bonds formed between them

Vertices with the Second Neighborhood Property in Eulerian Digraphs

The Second Neighborhood Conjecture states that every simple digraph has a vertex whose second out-neighborhood is at least as large as its first out-neighborhood, i.e. a vertex with the Second Neighborhood Property. A cycle intersection graph of an even graph is a new graph whose vertices are the cycles in a cycle decomposition of the original graph and whose edges represent vertex intersections of the cycles. By using a digraph variant of this concept, we prove that Eulerian digraphs which admit a simple dicycle intersection graph have not only adhere to the Second Neighborhood Conjecture, but have a vertex of minimum outdegree that has the Second Neighborhood Property.Comment: fixed an error in an earlier version and made structural change

Large-gap quantum spin Hall insulators in tin films

The search of large-gap quantum spin Hall (QSH) insulators and effective approaches to tune QSH states is important for both fundamental and practical interests. Based on first-principles calculations we find two-dimensional tin films are QSH insulators with sizable bulk gaps of 0.3 eV, sufficiently large for practical applications at room temperature. These QSH states can be effectively tuned by chemical functionalization and by external strain. The mechanism for the QSH effect in this system is band inversion at the \Gamma point, similar to the case of HgTe quantum well. With surface doping of magnetic elements, the quantum anomalous Hall effect could also be realized