Synthesis, crystal structures, and dye removal properties of a series of discrete and polymeric copper, zinc, cobalt, and cadmium complexes containing bis-pyridyl-bis-amine ligands

Abstract

Two bis-pyridyl-bis-amine ligands, trans-1,2-bis(m-picolyamino)cyclohexane (rac-m-picchxn) and trans-1,2-bis(p-picolyamino)cyclohexane (rac-p-picchxn), derived from trans-1,2-diaminocyclohexane (rac-chxn), were assembled with CuCl2, ZnCl2, ZnBr2, Co(NO3)2, and CdCl2 through reactants slow diffusion to afford corresponding metal complexes. Complexes [Cu(R,R-m-picchxn)Cl2] (1) and [Zn(rac-m-picchxn)Br2] (3) are mononuclear coordination structures, complex [Zn2(rac-m-picchxn)Cl4]n (2) adopts a one-dimensional (1D) helical chain, complex {[Co(R,R-p-picchxn)(NO3)2]·THF·2/3H2O}n (4) has a two-dimensional (2D) kgm layer structure, complex [Cd(rac-p-picchxn)Cl2]n (5) suits a 1D double-stranded zigzag chain structure, and compound [Cu(rac-chxn)2][CuCl3] (6) is a Cu(I)-Cu(II) mixed-valence ionic product generated from the hydrolysis of rac-p-picchxn associated with the reduction of Cu(II) ion. The two bis-pyridyl-bis-amine ligands possess a chelating-bridging mode in forming infinite network and a chelating-only mode in forming discrete complexes. These metal–organic architectures show the influence of metal ion combining with organic ligand and anion on the structure variation. Noteworthy, chain polymers 2 and 5 could be utilized in the removal of methyl orange (MO), acid orange 7 (AO7), and malachite green (MG) from water through adsorptive processes. The adsorption dynamics of MO and AO7 on 2 and MG on both 2 and 5 obeyed a pseudo-second-order kinetics while that of MO and AO7 on 5 followed a pseudo-first-order kinetics.