Structure, thermodynamics, and electronic properties are predicted for a new low energy phase of carbon which contains planar sheets equally occupied by sp2 and sp carbon atoms. The isolated planar sheets have the same planar symmetry as do the layers in graphite (p6m) and can be formally viewed as resulting from the replacement of one‐third of the carbon–carbon bonds in graphite by –C 3/4 C– linkages. This material, called graphyne, is predicted to have a crystalline state formation energy of 12.4 kcal/mol carbon, which appears to be much lower than for any carbon phase which contains acetylenic groups as a major structural component. Based on the major structural reorganization required for graphitization and the observed high temperature stability of known model compounds, high temperature stability is predicted for graphyne. While graphyne will have similar mechanical properties as graphite, it is predicted to be a large bandgap semiconductor (Eg=1.2 eV) rather than a metal or semimetal. Based on this...

Structure‐property predictions for new planar forms of carbon: Layered phases containing sp2 and sp atoms

Publisher Summary This chapter discusses the published X-ray investigations of organometallic compounds of Na, K, Rb, and Cs. Organometallic molecules are defined as having metal–carbon contacts or closely related structures. The chapter presents structures from the Cambridge Crystallographic Data Base that might be termed to be “organometallic” in this restricted sense, although representative examples of related compounds are included. Systems that are organic but contain metal heteroatom rather than metal–carbon contacts are illustrated and many structures through 1985 also are reported. The enhanced reactivity of the organometallic compounds of the heavier alkali metals is a desirable asset but may also lead to ready thermal decomposition. Aggregation of organoalkali compounds is essentially electrostatic; two or more M–C bond dipoles interact mutually with one another. With notable exceptions, the structures of organoalkali compounds have not been determined on the pure compounds. The NiAs-like arrangements allow the anions to invert or, in the extreme, to become planar. Ail compounds of the alkynyl type possess layered or three-dimensional structures.

Sodium, Potassium, Rubidium, and Cesium: X-Ray Structurai Analysis of Their Organic Compounds1

Electronic spectra of several TCNQ, complexes have been measured with single crystals by the transmission method. The assignment of electronic transitions are presented based on the electronic stru...

Electronic spectra and electronic structure of TCNQ complexes.

Hexagonal Layered Materials Composed of [M2(O2CCF3)4] (M=Ru and Rh) Donors and TCNQ Acceptors

Supercritical fluid separations of metal complexes in CO 2 have received little attention in the literature. This is believed to be caused by low solubilities of these compounds in supercritical CO 2 . The solubilities of several metals complexed with bis(trifluoroethyl)dithiocarbamate have been determined spectroscopi cally and their behavior in supercritical CO 2 studied using UV-VIS and FT-IR spectroscopy. Fluorination of the ligands in these metal chelates was found to increase solubilities of the complexes by several orders of magnitude.

P. Arthur

Papers

A refinement of the crystal structure of cesium tetracyanoquinodimethanide