Cu^II coordination polymers derived from bis-pyridyl-bis-urea ligands: Synthesis, selective anion separation and metallogelation

Abstract

The reaction of CuSO₄.5H₂O with a series of bis-pyridyl-bis-urea ligands equipped with aliphatic backbone such as N,N′-bis-(3-pyridyl)ethylene-bis-urea L1, N,N′-bis-(3-pyridyl)propylene-bis-urea L2 and N,N′-bis-(3-pyridyl)butylene-bis-urea L3 in aque-ous solution (metal: ligand ratio = 1: 2) resulted in four coordination polymers (CPs): [{Cu(H₂O)₂(SO₄) (L1) 1.5}.9.5H₂O]_∞ (1), [{Cu(H₂O)₃(SO₄) (L2)}.(H₂O) (EtOH)]_∞ (2a), [Cu(H₂O)₄(SO₄)(L2)₂]_∞ (2b) and [{Cu(1) (H₂O)₂(SO₄)₁(μ-L3)₃Cu(2)(H₂O)₂(SO₄)₁(μ-L3)₃}.20.5H₂O]_∞ (3). Except 2b which was concomitantly formed with 2a, all the CPs were characterized by single crystal X-ray diffraction. X-ray powder diffraction, FTIR and elemental analysis data confirmed that all the ligands were able to separate selectively, an important anion SO^2-₄ from a complex mixture of oxo-anions such as SO^2-₄, NO^-₃, ClO^-₄ and CF₃SO^-₃ in the form of the corresponding CPs. L3 formed a gel when it reacted with CuSO₄ in DMSO/H₂O and DMF/H₂O mixture with a minimum gelator concentration of 8-10 wt%, and the gel was characterized by tube inversion test, field emission scanning electron microscopy and rheology.