Brigitte E. Segmuller

Mechanical Stress and Reactivity in Organic Solids

Organic single crystals provide an ideal model for studying the factors that influence chemical processes in structured media. Reaction trajectories are well defined and reveal the influence of spontaneous mechanical stresses equivalent to tens of thousands of atmospheres. Analysis of molecular and crystal structures helps to explain both local mechanical properties, which influence reactions, and bulk properties such as melting point, compressibility, and surface energy.

Interpreting Substituent Effects on the Crystal Packing of Long-Chain Diacyl Peroxides. The Crystal Structures of D1 (11 Bromoundecanoyl) Peroxide and Di (Undecanoyl) Peroxide

Abstract Although crystals of di(11-bromoundecanoyl) peroxide and di(undecanoyl) peroxide have different space groups (P43212 and C2221), the molecules pack in almost identical layers. They differ only in the nature of stacking across interfaces involving the terminal groups. Because the 90° twist about the O-O bond locks neighboring molecules together within the layer, each peroxide shows a single solid phase from 5K to the melting point. Analysis of the stacking pattern in terms of the six possible orientational relationships suggests special stability for an L-shaped motif of C-Br-Br-C. Other substituents create different stackings of the same layer structure to give three crystal classes and five space groups among 14 compounds. Unsymmetrical peroxides are useful both for forcing a variety of substituted chains (particularly odd-even homologues) to pack with identical layer structures, and for controlling the stacking pattern. Because structural differences are localized in the vicinity of the substit...

Cluster condensation reactions: the synthesis and crystal and molecular structure of Os6(CO)14(μ2-PPh2)2(μ3-S)3(μ4-S)

Abstract Thermal degradation of the cluster compound Os3(CO)8(PPh2H)(μ3-S)2 (I) at 125°C leads to decarbonylation and formation of the new ligand bridged hexanuclear cluster Os6(CO)14(μ-PPh2)2(μ3-S)3(μ4-S) (II) in 11% yield. Space Group: P 1 , No. 2, a 10.427(5), b 13.552(3), c 17.919(3) A, α 84.87(2), β 75.41(3), γ 78.43(3)°, V 2399(2) A3 Z = 2, ϱcalc 2.82 g cm−3. The structure was solved by the heavy atom method and refined (3223 reflections) to the final residuals R = 0.042 and Rw = 0.036. The molecule consists of two sulfido bridged open triosmium clusters which are linked by a bridging sulfido ligand and a bridging diphenylphosphino ligand.