Weak Intermolecular Interactions in the Crystal Structures of Molecules with Tetrahedral Symmetry:  Diamondoid Nets and Other Motifs

Motif-forming characteristics of weak intermolecular interactions (Br····Br, C⋮CH····C⋮C, and C⋮CBr····C⋮C) were examined in the solid state structures, determined by single-crystal X-ray diffraction, of tetraphenylmethane and 1,3,5,7-tetraphenyladamantane derivatives substituted at the four vertices with bromo, ethynyl, bromoethynyl, and 1,3-diethynyl groups. The crystals of the bromo- and ethynyl-substituted tetraphenylmethane derivatives exhibited triply interwoven diamondoid lattices sustained by weak interactions between bromo and ethynyl groups. It was observed that when bromo- and ethynyl groups are interchanged in these compounds, their solid-state structures did not change significantly. The crystals of tetrakis(4-bromoethynyphenyl)methane, as well as 1,4- and 1,3,5-bromoethynylbenzene, were sustained by rare, T-shaped C⋮CBr····C⋮C contacts, but a comparison between these solid-state structures showed significant differences. All terminal 1,3-diynes were unstable compounds that decomposed rapidly. In general, it was observed that tetrahedral building blocks with a larger tetrahedral core, such as adamantane, formed disordered structures or fragile, highly solvated crystals.