THE STRONG AROMATIC HYDROGEN-BONDING IN CRYSTALLINE PROPARGYLAMMONIUMTETRAPHENYLBORATE

Crystalline propargylammonium tetraphenylborate contains strong N+-H a nd moderate C=C-H hydrogen bond donors, but no conventional accepters. Therefore, the donors can only form T-type hydrogen bonds with the ph enyl groups of the anion, leading to a dense system of aromatic hydrog en bonds which involves also the ethynyl groups. For the latter, this is the first documented case of C=C-H ... Ph hydrogen bonds in an ioni c compound; the infrared absorption spectrum shows very similar charac teristics as previously observed for C=C-H ... Ph interactions in unch arged systems. The distances of the donor H-atoms to the aromatic cent roids are in the range 2.08-2.37 Angstrom for N+-H and 2.55-2.77 Angst rom for C=C-H donors. (C) 1997 Elsevier Science B.V.