A Molecular Leverage for Helicity Control and Helix Inversion

The helical tetranuclear complex [LZn₃La(OAc)₃] having two benzocrown moieties was designed and synthesized as a novel molecular leverage for helicity control and helix inversion. Short alkanediammonium guests H₃N⁺(CH₂)_nNH₃⁺ (n = 4, 6, 8) preferentially stabilized the P-helical isomer of [LZn₃La(OAc)₃], while the longer guest H₃N⁺(CH₂)₁₂NH₃⁺ caused a helix inversion to give the M-helical isomer as the major isomer. The differences in the molecular lengths were efficiently translated into helical handedness via the novel molecular leverage mechanism using the gauche/anti conversion of the trans-1,2-disubstituted ethylenediamine unit.