Dinuclear double helicates with a twist: synthesis, structure and supramolecular entanglement in [M2L2] metallo-helices {M = Co(II), Cu(II), H2L = bis(N-salicylidene-4,4′-diaminodiphenyl)methane}

Abstract

Self-assembly of the tetradentate ligand bis(N-salicylidene-4,4′-diaminodiphenyl)methane, (H₂L), around Co(II) and Cu(II) gives rise to the dinuclear double helicates [Co₂L₂]·1.7CH₂Cl₂·0.6H₂O, (1) and [Cu₂L₂]·CH₂Cl₂ (2), which have been characterised by a single crystal X-ray diffraction study. Complexes 1 and 2 are structurally similar with two four coordinate metal centres in slightly distorted tetrahedral geometries in 1 and severely distorted tetrahedral geometry in 2. The different geometric preferences of Co(II) (tetrahedral) and Cu(II) (square planar) contort the ligands such that extended planarity is absent in 1 whilst present in 2. This distortion results in a tighter helical twist in 1 compared with 2, which consequently has a larger metal–metal separation. Complexes 1 and 2 each exhibit three-dimensional supramolecular entanglement brought about by elaborate inter-molecular π⋯π (face-to-face) and C–H⋯π interactions.