Construction of copper metal–organic systems based on paddlewheel SBU through altering the substituent positions of new flexible carboxylate ligands

Abstract

Three flexible dicarboxylate ligands 2,2′-(1,2-phenylenebis(methylene))bis(sulfanediyl)dibenzoic acid (H₂L⁶), 2,2′-(2,4,6-trimethyl-1,3-phenylene)bis(methylene)bis(oxy)dibenzoic acid (H₂L⁷) and 2,2′-(1,4-phenylenebis(methylene))bis-(sulfanediyl)dinicotinic acid (H₂L⁸), have been designed and synthesized. All ligands can adopt syn or anti conformations and the positions of the functional substituents in the central benzene ring change gradually from 1,2-, 1,3- to 1,4-position. By applying these flexible ligands to assemble with copper ions, four metal–organic complexes based on paddlewheel SBU have been isolated. Complexes 1 and 2 are discrete molecular chairs. Complex 3 is a 1D molecular-chair-based coordination polymer. The molecular chairs, similar to that found in 1 and 2, are infinitely connected by the bridging 4,4′-bipy ligands to result in the formation of the 1D chain structure. Complex 4 is a two-dimensional wavelike layer structure containing a 68-member ring. Both L⁶ and L⁷ in 1 and 2 adopt syn conformation, while L⁸ adopts anti conformation, which results in the formation of the 2D layer structure of complex 4.