Synthesis, Characterization And Properties Of Novel Lead(Ⅱ) Coordination Polymers

Crystal engineering is involved with the behavior of molecules or chemical groups within the crystal lattice, the control of crystal design and properties, and the prediction of crystal structures. Recently, the new research fields in the crystal engineering contain inorganic-organic hybrid materials, microporous material, molecular magnet and coordination polymers, et al. The design and synthesis of coordination polymers with unusual structures and properties are attracting increasing attention, not only for their interesting molecular topologies, but also for their potential applications as functional materials. With the broad use of the hydrothermal technique and the development of the analytical method, the coordination polymers are developed rapidly. Recently, the research on coordination polymer is mostly concentrated on the transition metals, while the main groups are rarely reported. Lead(II) compounds have unique structure and broad use. The aim of this work is to design and synthesize a series of metal-organic coordination polymers of Pb via the interaction between the metal and the ligands. In this thesis, a series of Pb(II) coordination polymers are synthesized, and their structures and properties are investigated. In the first chapter of five, the concepts, research methods, histories and new developments of coordination polymers are introduced. At the end of this chapter, we pointed out the importance of the search project and summarized the important results obtained in the thesisIn the second chapter, the Pb(II) and Cd(II) coordination polymers containing methyl orange which was used as pH indicator were synthesized for the first time under hydrothermal conditions. The synthetical conditions and the spectra of them were discussed. Methyl orange , Pb(NO3)2 and HCl resulted an one-dimensional coordination polymer Pb(MO)(phen)Cl (1) with chain-like structure connecting by the sulfonic group and Cl- anion. In this compound, the chains are interlaced to each other and give form to a supramolecular structure like slide fasteners. 1 is the first coordination polymer built up by methyl orange and Pb(II). In similar hydrothermal condition, with the reactant HCl changing into HNO3, compound 2 was obtained. Compound 2 has zero-dimensional structure with the neutral Pb(MO)2(phen)2(H2O) molecule as a unit, in which each Pb coordinates to two MO and two phen molecules. It is the Van der Waals interactions that assemble the Pb(MO)2(phen)2(H2O) units in compound 2 into three-dimensional structure. [Cd(en)2(H2O)2](MO)2 (3) was synthesized by Cd(II) salt and MO. In compound 3, there are two en and two H2O molecules coordinated with Cd center to form a [Cd(en)2(H2O)2]2+ unit. [Cd(en)2(H2O)2]2+ units and methyl orange anions are linked by H-bonds to form a 2-D supramolecular compound. The synthetic condition, characteristic of the structure, the response of IR and Raman spectrum to pH were discussed. The stability in acid and basic condition of 3 was primarily validated.In the third chapter, five Pb(II) coordination polymers constructed by the aromatic polycarboxylic acid Pb13Na(μ3-O)(μ3-OH)(BDC)12 (4), Pb4(μ4-O)(H2O)(1,3-BDC)3 (5), Pb(C8H4O4) (6), [Pb2(H2O)2(HBTC)2]·3H2O (7) Pb2(1,4-BDC)(ox)(H2O)3 (8) were synthesized. Compound 4, 5, 6 were synthesized under similar condition. They are all three-dimensional coordination polymers. Compound 4 was synthesized from Pb(II) and 1,3-BDC. The Pb12 cluster with a Na atom in center and the Pb12O20 cage constructed by the Pb12 cluster and twenty O atoms in compound 4 are reported for the first time. The diameter of inscribed sphere of the Pb12O20 cage is about 7.52?. The Pb12O20 cages are connected to each other via PbO8 units and form an infinite Pb-O chain.The coordination geometry of Pb1 and Pb2 ions in compound 4 are hemidirected, although the coordination numbers of them are high. It's the rigidity of the cluster that resists the symmetrical distribution of the bonds of Pb in a whole coordination sphere. In comparison with Pb1 and Pb2, Pb3 has less coordination number but holodirected geometry. In similar condisions with 4, compound 5 was obtained with a novel four-nucleus Pb cluster in it. In this cluster, four Pb ions occupy the vertexes of tetrahedron and aμ4-O atom occupies the center. They are connected by 1,3-BDC lignads to form an infinite three-dimensional framework with complicated topological structure. Compound 6 is a three-dimenstional framework, in which each Pb connects to six BDC molecules. The structure of compound 6 is also considered to be obtained from an infinite two-dimensional layer upheld by BDC. The interactions between Pb ions connect Pb ions into an infinite two-dimensional layer with honeycomb structure. Between each two adjacent Pb ions, there are twoμ2-O atoms. Compound 7 is a three-dimensional structure constructing from one-dimenstional chains by weak Pb-O bonds which are formed from the Pb ions and the O atoms on the protonized carboxyl of BTC on the other chain. Compound 8 is a three-dimensional coordination polymer containing BDC ligand and ox ligand which come from in-situ reaction. In this part, the effect of the weak coordination bonds on the coordination number, dimensionality, stability were also discussed. The mechanism of the in-situ reaction was analyzed.In hydrothermal condition, several Pb(II) coordination polymers with flexible aliphatic acid ligand [Pb6(H2O)2(cit)4]?3H2O (9),Pb(tar)(H2O)2 (10),Pb(C6H8O4) (11),Pb(C4H4O4) (12),Pb2(C6H6NO6)(NO3) (13) were synthesized. The effect of the temperature, ratio of the reactant on the synthesis were discussed. Compound 9, 11, 12 have three-dimensional structure, while compound 10 is one-dimensional chain-like framework, which is connected to three-dimensional supramolecular structure by H-bonds. Compound 13 is the first Pb(II) three-dimensional coordination polymer containing nta ligand. The similar Pb2(CO2)2 units forming by two Pb ions and two carboxyls in the compound 11, 12, 13 were investigated. In compound 13, the Pb2(CO2)2 unit is separate from each other, while it is connected into one-dimensional parallel chains in compound 11 and three-dimensional framework by sharing Pb ions in compound 12.