Crystal chemistry of tetraradial species. Part 5. Interaction between cation lone pairs and phenyl groups in tetraphenylborates: crystal structures of Me3S+,Et3S+,Me3SO+,Ph2I+, and 1-azoniapropellane tetraphenylborates

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Determination of the crystal structures of the tetraphenylborates of the trimethylsulfonium (Me3S+,P21/n), triethylsulfonium (Et3S+,Cmcm), trimethylsulfoxonium (Me3SO+,P21/m), diphenyliodonium (Ph2I+,Pnma), and 1-azoniapropellane (C10H18N+,P21/n) cations has shown that when regions of high local electron density (lone electron pairs) are present in the cation, the cation orients itself so as to minimize the repulsion between the lone pair(s) and the nearest anion phenyl groups, i.e. the cation orientation responds to the lone pair – aromatic π system interaction. This behaviour contrasts with the formation of H …π hydrogen bonds in tetraphenylborates of organic ammonium cations containing N-hydrogens and provides corroborative evidence for our previous finding: (1) given the opportunity, a cation N-hydrogen will form a hydrogen bond to a phenyl group(s) of the anion; (2) the orientation of the cation to form the N—H(N) …π bond is thus a manifestation of a positive hydrogen-bonding tendency rather than a passive response to overall packing requirements in the crystal. The geometries of the above cations are compared to those reported in the literature and those of Me3S+ and Me3SO+ have also been optimized by ab initio (RHF/6-31G*) methods.