Antimony lone electronic pair as a stereoelectronic barrier to stibatrane

To examine the effect of 5s(2) lone electron pair of antimony atom on the reaction of antimony trifluoride and triethanolamine in the presence of sodium methylate, the crystal structure of the reaction product -2-fluoro-6-(2-hydroxyethyl)-1,3-dioxa-6-aza-2-stibacy-cylooctane (1-fluoro-2-hydrostibatrane) FSb (OCH2CH2)(2)NCH2CH2OH) was confirmed. In the compound structure, the hydrogen atom of the 2-hydroxyethyl group of each molecule forms an intermolecular hydrogen bond with the oxygen atom of one of the five-membered SbOCH2CH2N half-cycles in a neighbouring molecule. A geometry of both five-member N-C-C-O-Sb heterocycles, end-capped by transannular N -> Sb bond in the 1-fluoro-2-hydrostibatrane molecule, is almost identical. C-O, C-C, N-C interatomic distances and valence angles in two endocyclic units (NCCOSb) are comparable to those observed in RSi(OCH2CH2)(3)N silatranes. A coordination polyhedron of the Sb atom can be represented as a transition from a bisphenoid to Sb(O-3)N trigonal pyramid, with a nitrogen atom at the apex and three oxygen atoms in the base. The N -> Sb transannular coordinate bond length is 2.402(4) angstrom, which is 0.40 angstrom greater than the Sb-N covalent bond standard length. The Sb-F bond (1.997(4) angstrom) is 0.12 angstrom longer than that in the SbF3 molecule, and insignificantly shorter than that of the Sb-F-ax (2.028(3) angstrom) in the SbF3 center dot Gly crystalline complex. The fluorine atom substantially strays from the N -> Sb axis to the direction of O(1) and O(2) atoms. The oxygen atom of the 2-hydroxyethyl group lies at a distance of 2.899(3) angstrom from that of Sb, intermediate between the valence bond length and the sum of the Van der Waals radii of these atoms. Combined with the F atom position, one can assume the 1-fluoro-2-hydrostibatrane crystal structure as a "frozen" state of the S(N)i(Sb) type nucleophilic attack of the oxygen atom, uncompleted because of its repulsion by the 5s(2) lone electronic pair of antimony atom.