The isothiocyanate complex of triphenylborane forms an unusual coordination polymer with [K(18-crown-6)]+, both in the solid state and in solution
Abstract
The title salt, (1,4,7,10,13,16-hexaoxacyclooctadecane-κ6O)[(isothiocyanato)triphenylborato-κS]potassium(I), [K(C19H15BNS)(C12H24O6)] or [K(SCNBPh3)(18-crown-6)], where 18-crown-6 is 1,4,7,10,13,16-hexaoxacyclooctadecane and [SCNBPh3]− is the (isothiocyanato)triphenylborate anion, exhibits a supramolecular structure that is best described as a helical coordination polymer or molecular screw. This unusual supramolecular structure is based on a framework in which the SCN− ion bridges the chelated K+ ion and the B atom of BPh3 in a μ2 fashion. The X-ray crystal structure of the title salt has been determined at 100 (1) and 293 (2) K. The K+ ion exhibits axial ligation by the S atom of the [SCNBPh3]− anion, with a K—S distance of 3.2617 (17) Å (100 K). The trans-axial ligand is an unexpected η2-bound C=C bond of a phenyl group (meta- and para-C atoms) that belongs to the BPh3 moiety of a neighboring molecule. The K—C bond distances span the range 3.099 (3)–3.310 (3) Å (100 K) and are apparently retained in CDCl3 solution (as evidenced by 13C NMR spectroscopy). By virtue of the latter interaction, the supramolecular structure is a helical coordination polymer, with the helix axis parallel to the b axis of the unit cell. IR spectroscopy and semi-empirical molecular orbital (AM1) calculations have been used to investigate further the electronic structure of the [SCNBPh3]− ion.