Cornering the 13th vertex: The first 13‐vertex carborane (see picture, B: brown, C: gray, H: white) has been prepared by a methodology that can in principle be applied repeatedly, leading to 14‐, 15‐, 16‐, …︁ vertex carboranes in the future. The 13‐vertex species has a henicosahedral geometry, not the docosahedral one expected, but the two forms are found to be very close in energy by DFT calculations.

Mound Laboratories has been investigating pyrotechnic materials for several years. Prior studies on the mechanism of ignition have been performed on Ti/KCIO, and Ti/ZB mixtures. Tbese studies have shown the importance of the surface oxides of these materials in determining the mechanism of ignition. In the present study, XPS spectra of fused metal, oxidized fused boron and boron metal powder have been recorded. The spectra are interpeted by including the presence of a continuous boron suboxide layer. The results presented here are different from those previously reported, which suggests that the formation of boron oxide occurs in islets. The predominant suboxide will be shown to be B,O,, where x/y = 3. This oxide was found to be present independent of the degree of oxidation. Including this oxide in thickness calculations shows the oxidation of powders to be five layers or so thick, and also aids in understanding Ti/ZB ignition.

Titanium-boron pyrotechnic reactions are essentially gasless, are very exothermic, and are known to initiate only at extremely high temperatures. The reactants are stable in normal laboratory environments and require no special sample handling, such as inert storage. These factors make the titaniundboron mixture ideal for one-shot thermal heat source applications. Mound has been investigating energetic material ignition properties for a number of years. Pyrotechnic mixtures of TiH,/KCIO, have revealed that the surface composition of the titanium fuel was TiO, and its presence on the fuel's surface controls the TiH, + KCIO, reaction. In the present study the surface chemistry of titanium and of boron have been examined before ignition. To understand the effect of temperature on the reactants and the mixture, titanium powder, boron powder, and blends were analyzed at ambient and elevated temperatures. XPS, TG and DTA results presented will show that the oxide on boron is the controlling factor in the ignition mechanism of the titanium-boron pyrotechnic reaction.

Reduction of 1,2-closo-C2B10H12 followed by treatment with [RuCl2(p-cymene)]2(p-cymene = C6H4MeiPr-1,4) affords the 13-vertex ruthenacarborane 4-(p-cymene)-4,1,6-closo-RuC2B10H12, characterised both spectroscopically and, in two crystalline forms, crystallographically. Although asymmetric in the solid state, having a docosahedral cage architecture with cage C atoms at vertices 1 and 6, this species clearly has Cs symmetry on the NMR timescale at room temperature. However, the fluctional process in operation can be arrested at low temperature, and an activation energy of 43.1 kJ mol(-1) is estimated. A computational study of the related species 4-(eta-C6H6)-4,1,6-closo-RuC2B10H12 reveals that the fluctionality is due to a double diamond-square-diamond process, first suggested by Hawthorne et al for the analogous CpCo species. These calculations yield an activation energy of 40.4 kJ mol(-1), in excellent agreement with that derived from experiment. Reduction of 1,2-Ph(2)-1,2-closo-C2B10H10 followed by treatment with [RuCl2(eta-C6H6)]2 or [RuCl2(p-cymene)]2 yields the analogous species 1,6-Ph2-4-(eta-C6H6)-4,1,6-closo-RuC2B10H10 and 1,6-Ph2-4-(p-cymene)-4,1,6-closo-RuC2B10H10, respectively. These C,C-diphenyl compounds were again studied spectroscopically and crystallographically, the p-cymene species again showing two crystalline modifications. In contrast to their CpCo and Cp*Co analogues all three ruthenacarboranes do not undergo isomerisation in refluxing toluene.

Attempted crystallographic studies of the known compounds 4-Cp-4,1,8-closo-CoC2B10H12 and 4-Cp-4,1,12-closo-CoC2B10H12 were frustrated because of disorder which was impossible satisfactorily to model. Thus the family of Cp* compounds 4-Cp*-4,1,6-closo-CoC2B10H12, 4-Cp*-4,1,8-closo-CoC2B10H12 and 4-Cp*-4,1,12-closo-CoC2B10H12 were prepared. The 11B NMR spectroscopic properties of these compounds are closely similar to those of their Cp analogues. All three compounds were studied crystallographically. The 4,1,8- and 4,1,12-species are isomorphous and partially disordered, however the disorder was successfully modelled and structural analyses of 4,1,8- and 4,1,12-MC2B10 compounds are reported for the first time. A new technique for distinguishing between cage C and B atoms in crystallographic study of (hetero)carboranes is reported. The 12-vertex compound 3-Cp*-3,1,2-closo-CoC2B9H11 is formed as a minor co-product along with 4-Cp*-4,1,6-closo-CoC2B10H12 and is believed to result from partial degradation of the latter. The 12-vertex species has also been subjected to crystallographic analysis.