Selective Separation of the Sulfate Anion by In Situ Crystallization of CdII Coordination Compounds Derived from Bis(pyridyl) Ligands Equipped with a Urea/Amide Hydrogen‐Bonding Backbone

Abstract

AbstractFive new coordination compounds, namely [{Cd(μ‐L1)(μ‐SO4)(H2O)2}·MeOH]∞ (1), [{Cd(μ‐L2)2(SO4)(H2O)}·3.5H2O]∞ (2), [{Cd(μ‐L3)(SO4)(H2O)3}·MeOH]∞ (3), [{Cd(L4)4(H2O)2}·SO4·8H2O] (4) and [{Cd(μ‐L5)(μ3‐SO4)(H2O)}·2H2O]∞ (5), [L1 = N‐(3‐picolyl)‐N′‐(3‐pyridyl)urea, L2 = N‐(4‐picolyl)‐N′‐(3‐pyridyl)urea, L3 = N,N′‐di‐3‐pyridylurea, L4 = N,N′‐di‐4‐pyridylurea and L5 = N,N′‐di‐3‐pyridylnicotinamide] have been synthesized and characterized by single‐crystal X‐ray diffraction. It is revealed that the positional isomers L1,L2 and L3,L4 play a crucial role in determining the resultant supramolecular structures of 1–4. Various supramolecular architectures, that is, a 3D coordination polymer (1), a 1D looped‐chain coordination polymer (2), a 1D zigzag coordination polymer (3), a discrete coordination complex (4) and a 2D corrugated sheet (5), were observed. In situ crystallization of compound 2 under competitive crystallization conditions inthe presence of competing anions such as SO42–, NO3–, ClO4–,AcO–, Cl– and Br– resulted in the isolation of 2, which indicates the selective separation of SO42– from an aqueous mixture of other competing anions, as revealed by FTIR spectroscopy, X‐ray powder diffraction and elemental analysis. The X‐ray structure of 2 indicates that both intermolecular hydrogen bonding and metal–ligand coordination of SO42– play an important role in the selective separation of SO42–. A similar competitive crystallization also resulted in selective SO42– separation in the form of compound 5, as determined by FTIR spectroscopy and elemental analysis.