Trigohexagonite: A Rare Three-Dimensional Network of Quaternary Stoichiometry

A novel 3-,4-connected network is reported in this communication that is a rare example of a three-dimensional (3D) network with a quaternary stoichiometry, in which 4 distinct sites of bonding occur in the unit of pattern of the material. The net lies in the hexagonal space group P-6m2 (#187) and there are 10 vertices (or atoms) in the unit cell, including 4 sites of approximately trigonal planar coordination and 6 sites of approximately tetrahedral coordination. All vertices (atoms) in the network sit on special positions in the P-6m2 space group, giving the network high 6-fold symmetry axes parallel to the crystallographic c-axis. The structure has thus been named trigohexagonite in a loose analogy with its hexagonite crystalline homolog, sitting in the hexagonal space group P6/mmm (#191). The Wells point symbol for the trigohexagonite network is given by (73 )(63 83 )3(6.72 )3(3.74 .8)3 where this symbol indicates the quaternary stoichiometry of the network. The Wells point symbol also reveals that the only structural strain present in the network comes from the presence of the 3-gon, cyclopropane-like moieties in it, built on tetrahedral vertices. This structural motif of cyclopropane-like rings has precedent in organic chemistry and it adds character to the overall 6-fold symmetry of the trigohexagonite pattern. Also, the overall network contains rare trimethylenemethane-like clusters of 4 trigonal planar vertices (atoms), bonded together, that constitute the 3- connected component of the network. Both C10 and B10 realizations are briefly described.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Application of the PM6 method to modeling the solid state

The applicability of the recently developed PM6 method for modeling various properties of a wide range of organic and inorganic crystalline solids has been investigated. Although the geometries of most systems examined were reproduced with good accuracy, severe errors were found in the predicted structures of a small number of solids. The origin of these errors was investigated, and a strategy for improving the method proposed

Trigohexagonite: A Rare Quaternary Stoichiometry Network

A rare quaternary stoichiometry network of high hexagonal symmetry (P-6m2) is described. A set of hexagonal fractional crystallographic coordinates, for both an idealized network, and optimized boron and carbon allotropic realizations are described along with their band structures. Both should be metallic phases

Squaroglitter: A 3,4-Connected Carbon Net

Theoretical calculations are presented on a new hypothetical 3,4-connected carbon net (called <i>squaroglitter</i>) incorporating 1,4 cyclohexadiene units. The structure has tetragonal space group <i>P</i>4/<i>mmm</i> (No. 123) symmetry. The optimized geometry shows normal distances, except for some elongated bonds in the cyclobutane ring substructures in the network. Squaroglitter has an indirect bandgap of about 1.0 eV. The hypothetical lattice, whose density is close to graphite, is more stable than other 3,4-connected carbon nets. A relationship to a (4,4)­nanotube is explored, as is a potential threading of the lattice with metal needles