Selective anionic dye adsorption, topology and luminescence study of structurally diverse cadmium(ii) coordination polymers

Abstract

A flexible carboxylate EGTA (ethylene bis(oxyethylenenitrilo) tetraacetic acid) ligand was used to construct four coordination polymers, namely, {[Cd₃(EGTA)(NO₃)₂(H₂O)₆]·H₂O}_n1, {[Cd₅(EGTA)₂(bpy)₄(H₂O)₄]bpy·(NO₃)₂·(H₂O)₈}_n2, {[Cd₃(EGTA)(1,2-dpe)_1.5(H₂O)₃](NO₃)₂(H₂O)₆}_n3 and {[Cd₂(EGTA)(dpe)(H₂O)]·(H₂O)₄}_n4, bearing N-donor pyridyl co-linkers 4,4′-bipyridine (bpy), 1,2-di(4-pyridyl)ethane (1,2-dpe) and 1,2-di(4-pyridyl)ethylene (dpe), under solvothermal conditions. Complexes were characterized by spectroscopic and single crystal X-ray diffraction techniques to explore binding manners, geometries, dimensions and involvement of non-covalent interactions in stabilization of the structure. Complexes 1 and 3 afforded 1D zigzag infinite chain structure stabilized by hydrogen bonding of co-crystallized water molecule with uninodal 2C1 and 2,2,4C3 topologies, respectively. In contrast, complexes 2 and 4 displayed 3D sheet frameworks with 4,6-c net-connected fsc and sqc11 and uninodal 6-c net connected rob topologies, respectively. Cd(II) exhibits rare distorted trigonal pyramidal geometrical configuration in complex 3. The complexes also show solid state emission properties. Furthermore, evaluation of dye adsorption properties of complexes indicates that complexes 2 and 3 selectively adsorb anionic dyes (methyl orange and Congo red) quickly (within 30 and 90 minutes, respectively), while complex 4 adsorbs anionic dye in a longer time (∼24 h). The adsorption capabilities of complexes 2 and 3 are stronger, possibly owing to the cationic nature of the complexes and greater non-covalent interactions compared to complex 4.