THORIUM SILICIDE

Hoffmann et al. published a theoretical communication of a C allotrope model based upon the anionic silicon sub-lattice of thorium silicide. It is comprised of parallel polyacetylene-like chains, in layers, that are joined to neighboring layers, in an orthogonal fashion, by staggered 3-3 bonds, to generate the full 3-dimensional C lattice. The network is perhaps favorable based upon the precedent of chemically stablilized polyacetylene-like substructures from which the lattice is generated. The only drawback to the model is the staggered 3-3 bonds...the p orbitals of which, nonetheless, participate in electronic delocalization, and stabilization, along their respective tetragonal lattice a-axis and b-axis, oriented, polyacetylene-like substructure directions. It remains an important target for synthesis from graphite, or perhaps separation or isolation from natural C sources such as coal or petroleum. The layers of conjugated p orbitals, pointing in alternating layers in one orthogonal direction, and then the other direction, confer a metallic status to the material as a novel, 3D conjugated, organic lattice...There is metal more attractive.

SQUARE PYRAMID COORDINATION

There is a tetragonal cell (P4/mmm) of all square pyramid coordination that I thought of and showed to Professor O'Keeffe in an email exchange and he showed me that it was already proposed by his people...it was comprised of 2 opposing square pyramid coordination sites linked to other such opposed dimeric square pyramid coordination units...I do not know the stoichiometry from memory but the Schlaefli symbol was (5 1/5, 5) I believe. It was almost the continuation of the sequence (3, 3), the tetrahedron to (4, 4) the square net...on to (5, 5) as a novel 3D network...almost but not quite.

SODIUM NITRIDE ELECTRIDE

One time I wrote down a drawing of a Fm-3m unit cell with sodium cations in the faces and a nitride dianion in the center and electrons on the corners to form a perovskite-like sodium-nitride-electride as a novel inorganic perovskite-electride...I sent the drawing to Professor DiSalvo in 1992 about...he answered me for me to come down to talk to him about nitrides and electrides...I saw him some times after that but we never had a chance to talk about nitrides and electrides...I will make a drawing of the structure some time and scan it in and send the scan to Roald and to Jon with some background comments on it...it might exist

NON-CHEMICAL NETWORKS

There are also non-chemical networks that have structures, that do not correspond to any known type of chemical bonding genre...there may in fact be more of these non-chemical networks, than there are networks that correspond to chemistry...an example of a non-chemical network type is any pattern that involves a 3-3 bond that is staggered and not eclipsed...in such a motif the p-orbitals of the ordinary pi bond are perpendicular to each other making a pi bond formation impossible...Wells, in his great work, "Three Dimensional Nets and Polyhedra", shows a photograph of at least one such non-chemical network, which is just a 3-,4-connected pattern in uniform 8-gon circuits...in addition there may be some Andreini or non-Andreini space fillings of polyhedra that can be transformed over to non-chemical networks, including those with vertices which, in-plane, connect to more than 6 other points...like an 8-fold coordinated in-plane vertex, translated over from an octagonal parallelohedron, within some Andreini, or perhaps, non-Andreini space filling of polyhedra, for example...such space fillings would not have any chemical analogue and they may be more numerous than other space fillings of polyhedra with chemical analogues..