Crystallographic evidence for different modes of interaction of BF3/BF4- species with water molecules and 18-crown-6

H. Feinberg, I. Columbus, S. Cohen, M. Rabinovitz, H. Selig, G. Shoham*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


We report the crystal and molecular structures of the complex of 18-C-6 with H3O+BF4- (I) and the complex of 18-C-6 with BF3OH2·H2O (II). The different modes of appearance of the "BF3" species as BF3, BF3OH2, BF3OH2·H2O and BF4-, as well as their structurally significant intermolecular and intramolecular interactions, are discussed. In complex I the oxonium ion is bound at the centre of the 18-C-6 macrocycle. The oxonium oxygen is located practically equidistant (2.68-2.73 Å) from the six macrocyclic ethereal oxygens. The BF4- counter-ion is positioned 7.3 Å away from the oxonium ion in the same general plane of the crown ether. This anion is not involved in any direct intermolecular contacts, a fact that may explain why it is spherically disordered. In complex II there is no guest molecule (or ion) present in the "cavity" of the macrocycle, but there are two hydrogen-bonded systems of BF3OH2·H2O that are interacting with the crown ether on either side of the general macrocyclic plane. Complex II features three types of hydrogen bonds-the O(water)-H⋯O(crown) bonds (2.83 and 2.85 Å), the O(water)⋯H-O(BF3) bond (2.49 Å) and the O(BF3)-H⋯O(crown) bond (2.65 Å). The strong intermolecular O(crown)⋯O(water)⋯O(BF3) and O(crown)⋯O(BF3) interactions stabilize the normally unstable BF3OH2·H2O species.

Original languageAmerican English
Pages (from-to)2913-2919
Number of pages7
Issue number24
StatePublished - Dec 1993


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