A Molecular Leverage for Helicity Control and Helix Inversion

The helical tetranuclear complex [LZn<sub>3</sub>La(OAc)<sub>3</sub>] having two benzocrown moieties was designed and synthesized as a novel molecular leverage for helicity control and helix inversion. Short alkanediammonium guests H<sub>3</sub>N<sup>+</sup>(CH<sub>2</sub>)<sub><i>n</i></sub>NH<sub>3</sub><sup>+</sup> (<i>n</i> = 4, 6, 8) preferentially stabilized the <i>P</i>-helical isomer of [LZn<sub>3</sub>La(OAc)<sub>3</sub>], while the longer guest H<sub>3</sub>N<sup>+</sup>(CH<sub>2</sub>)<sub>12</sub>NH<sub>3</sub><sup>+</sup> caused a helix inversion to give the <i>M</i>-helical isomer as the major isomer. The differences in the molecular lengths were efficiently translated into helical handedness via the novel <i>molecular leverage</i> mechanism using the gauche/anti conversion of the <i>trans</i>-1,2-disubstituted ethylenediamine unit.