Sodium ion assisted molecular self-assembly in a class of Schiff-base copper(II) complexes

Syntheses, characterization and crystal structures of three new sodium based heterotrinuclear ionic clusters [(CuL1)2Na(ClO4-O,O′)(OH2)]·C8H8O2 (1), [(CuL2)2Na(ClO4-O,O′)] (2) and [{Cu(L3)2}2Na]+·ClO4− (3) derived from three different Schiff bases (L1 = 1:2 condensation of 1,2-propane diamine and o-hydroxy acetophenone, L2 = 1:2 condensation of 1,2-propane diamine and 2-hydroxy-5-methoxy acetophenone and L3 = 1:1 condensation of 2-amino pyridine and 3-ethoxy salicylaldehyde) are reported herein. The crystal structure analysis reveals that the square-planar Cu–ligand complexes act as building block for the trinuclear complex in which Na+ ion guides the orientation of Cu(II) Schiff-base complexes into a scissor like architecture in 1 and 2. The unique assembling feature of Na+ ion is also evident in complex 3 where even in the presence of a widely different Schiff-base ligand, Na+ guides two Cu(II)(L3)2 complexes to assemble around it in a crown ether like environment. In complexes 1 and 2 the square planar metal coordination provide suitable sites for chelate ring π···π interaction and Cu···π interaction which ensures columnar assembly of trinuclear units at the supramolecular level. The present study reveals the unique nature of the self-assembly of square-planar Cu(II) Schiff-base complexes around Na+.

Graphical abstractThree coordination complexes of Cu(II) and Na+ based on three Schiff base ligands show that square planar Cu(II)-Schiff base coordination complexes can act as building blocks which can be organized by Na+ ions in a novel scissor and crown ether like topology.Figure optionsDownload full-size imageDownload as PowerPoint slide