Copper(II)-assisted self-assembly of bis-N, O-bidentate Schiff bases: new building blocks for a double-helical supramolecular motif

摘要

Copper(II)-assisted self-assembly of a new bis-N,O-bidentate Schiff base ligand, bis(N-salicylidene-3,3'-diaminodiphenyl) sulfone (L~1) with two chelating sites linked by a spacer group (-C_6H_4SO_2C_6H_(4~-)), afforded in high yield the double-helical tetranuclear supramolecular complex with eight components. Single-crystal X-ray analyses demonstrated clearly that two Cu~(II) centers have a distorted tetrahedral (T_d) coordination sphere, whereas the other two remaining Cu~(II) have a square-planar coordination sphere. An analogous Schiff base, bis(N-salicylidene-4,4'-diaminodiphenyl) ether (L~6) with a phenyl ether spacer (-C_6H_4OC_6H_(4~-)) was also designed to self-assemble in the presence of metal ions, leading to a double-helical dinuclear supramolecular motif. Electrospray mass spectrometry proved a very useful characterizational tool to detect a variety of supramolecular species in solution. These unprecedented double-helical motifs in solid and solution seem to be induced by the geometrical preference for tetrahedral and/or square-planar coordination of copper(II) ion and the interligand aromatic interactions between the bridging groups of L~1 and L~6.