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

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.