Supramolecular Encapsulation Formed By Second-Sphere Coordination

Supramolecular chemistry is a new and promising subject. Second-sphere coordination-the interaction between already coordinatively saturated metal complexes and external ligands (e.g. hydrogen bonding)-has demonstrated its potential in modulating the chemical, electrochemical, and photochemical properties of transition metal complexes by designed external second-sphere ligands.5,5'-diamino-2,2'-bipyridine (DABP) is used as the first-sphere ligand which possesses dual functions of coordination to metal ions through the bipyridyl moiety and hydrogen-bonding to external ligands through the amino groups. The primary complexes, [M(DABP)3]n+ are then reacted with certain second-sphere ligands to construct second-sphere hydrogen-bonded networks.This dissertation consists of two parts. Chapter 1 is the introduction and a brief review of literature work based on pyridine urea receptor binding sufate and second-sphere coordination. Chapter 2 shows the details of the experiments, results and discussion. The main results are as follows:Recently we reported a tren-based tris(3-pyridylurea) compound (N-[2-[bis[2-[N'-(3-pyridyl)ureido]ethyl]-amino]ethyl]-N'-(3-pyridyl)urea, L1) which can encapsulate sulfate anion in the cavity formed by two L1 molecules in the hydrogen-bonded architecture [M(H2O)6][SO4cL2] (1) (M=Mn (la), Zn (1b)) from the reaction of MSO4 with L. We choose the bigger size of [Fe(DABP)3]SO4 complex to assemble with the ligand L1, and [Fe(DABP)3][SO4cL]-10H2O (2) were obtained. In the compounds 2, each ligand molecule includes a sulfate anion in its cleft via multiple hydrogen bonds and forms a half-encapsulation model. According to the feature of compounds 1 and 2, two complexes [Fe(DABP)3][SO4(?)L2] (3) and [Fe(DABP)3(?)L2][SO4(?)L2] (4) which encapsulate sulfate anion were crystallized by adding to two and four equivalent of L respectively. In the compound 3, anion encapsulation provided by two L and one sulfate is very similar with 1 and connects with [Fe(DABP)3]2+ cation by water molecules. As this system stretch, complexes 4 are obtained. After sulfate is in saturation, two mole L form a bigger cavity to encapsulate [Fe(DABP)3]2+cation. The new model belonges to which the same receptor L can bind both anion and cation simultaneously and respectively. To move forward a step, we focus on the selectivity of L:three allomerism compounds [M(DABP)3cL2] C12-24H2O (5) (M=Fe,Ni,Cu) are gaind by the reaction of [Fe(DABP)3]Cl2 with L. Interestingly, the tripod L firstly selects and binds [Fe(DABP)3]2+ cation and 30 member water-chlorine ring is formed surrounding cation encapsulation. This results shows that the order of selectivity for L is SO42-> [Fe(DABP)3]2+>Cr...