Synthesis And Anion Recognition Of Bis-(Pyridylurea) Ligands

Anion recognition is now a major field within supramolecular chemistry.The design of important anion receptors for biology,medicine and environment has recently grown into a rich area of research in supramolecular chemistry.Urea-based pyridyl ligands have drawn much attention in recent years due to their capacity of coordinating with metal ions by the pyridyl group and binding anions by the urea functionalities.We have designed two bis(pyridylurea) ligands,N,N'-ethane-1,2-diylbis(3-pyridin-3-ylurea) (L¹),N,N'-pentane-1,5-diylbis(3-pyridin-3-ylurea)(L²) and synthesized four new compounds,including three oxo-acid adducts and one transition metal coordination polymer.All new compounds have been fully characterized by IR,¹H NMR spectroscopy,and elemental analysis.The crystal structures of ligands L¹ and compounds 1-4 have been determined,and the hydrogen bond patterns,Ï€-Ï€stacking interactions and supramolecular structures have been discussed in detail.In particular, the anion binding modes and anion selectivity in these systems have been investigated.This thesis consists of four parts.Chapter 1 is the introduction and a brief review of literature work.Chapters 2-4 present the details of the experiments,results and discussion.The main results are as follows:1).Two bis(pyridylurea) ligands,N,N'-ethane-1,2-diylbis(3-pyridin-3-ylurea)(L¹), N,N'-pentane-1,5-diylbis(3-pyridin-3-ylurea)(L²) have been prepared and characterized. The structure of L¹Â·2H₂O has been determined by X-ray single crystal diffraction,which reveals that each water molecule binds three ligand molecules via four hydrogen bonds to form a three-dimensional layered hydrogen-bonded network.2).In order to gain insight into the anion binding properties of the ligands,we have synthesized three acid adducts of L¹,[(L¹H₂)(ClO₄)₂](1),[(L¹H₂)(CF₃COO)₂·2H₂O](2), and[(L¹H₂)(SO₄)](3).The solid-state structures of these anion complexes show that the overall coordination number(i.e.,number of hydrogen bonds) of the anions is two for the perchlorate 1,three for the trifluoroacetate 2,and six for the sulfate 3.It is found that the doubly protonated ligand binds the sulfate ion through the urea NH groups and the pyridinium N⁺H donor.However,the pyridinium N⁺H is not involved in hydrogen-bonding interactions with the anions in 1 or 2.In addition,we have examined the anion selectivity of L¹ through powder x-ray diffraction,and found that it showed a remarkable preference for the sulfate ion over perchlorate or trifluoroacetate ion.3).A coordination polymer of L²,[Zn(L²)₂(H₂O)₂]SO₄·2H₂O(4) has been prepared and characterized by X-ray single crystal diffraction analysis.Compound 4 has a novel three-fold interpenetrated framework structure.The SO₄^2- ions are enwrapped in elliptic cavities via eight hydrogen bonds from four urea groups.The sulfate recognition property of complex 4 has been discussed.