DESIGN AND FUNCTION OF THE SELF-ASSEMBLED NANO-RINGS

点击翻译按钮获取中文摘要

In order to construct the nano-sized polygons or polyhedra by the combination of Ag^+ and flexible aromatic amine ligands, we decided to use N, N'-bis(4-pyridyl)benzylamine (1). B3LYP/3-21G calculations after the conformation analysis by MMFF of 1 showed that the N_<(1)>-N_<(2)>-N_<(3)> angle of the most stable conformer is about 109.7°, which is exactly the same as that of X-ray structure of ligand 1. The Ag^+ induced ^1H-NMR and UV-VIS titration experiments were carried out in order to investigate the stoichiometry between Ag^+ and 1 in solution. Both titration results suggest that ligand 1 forms a (1:1)_n complex with Ag^+ ion in solution. A solid 1-AgOTf complex was obtained by mixing equimolar amount of ligand 1 in CH_3CN and AgOTf in CH_3OH in an N_2 atmosphere. After two days, single crystals precipitated quantitatively. The stoichiometry between ligand 1 and Ag^+ ion in the complex was studied by FAB-MS using m-nitrobenzyl alcohol. The FAB-MS also suggests that the stoichiometr … More y between ligand 1 and Ag^+ in the complex is (1:1)_n. The X-ray crystallography of 1-AgOTf complex was measured at 90K. The complex is a discrete cyclic hexamer (1:Ag^+ = 6:6) including six OTf ions and the hexamer is in the form of a hexagon. There is a large cavity in the center of the complex. Because of the disorder of atoms in the cavity, the solvent atoms in the cavity were not specified at 90K. The diameter of the cavity is about 20Å (Ag-Ag distance: 21.2Å and N_<(2)>-N_<(2')> distance: 21.7Å). Interestingly, the hexagon is not planer, but forms a chair conformation somewhat like the chair-form of cyclohexane. The N_<(2)> atoms are at the corners of the chair structure. The N_<(1)>-N_<(2)>-N_<(3)> and the N_<(1)>-Ag-N_<(3')> bond angles in the complex are 109.7° and 170°, respectively. A nano chair at the center overlaps with six nano chairs from one side, and a total twelve nano chairs from both sides. The nano chairs stack on each other and make honeycomb-like cavities. The atoms that participate overlapped sites are shown by ball-and-stick models. There are two kinds of face-to-face π-π stacking (pyridine-pyridine stacking: yellow-blue, benzene-benzene stacking: yellow-red) sites. The carbon-carbon distances and Ag^+-Ag^+ distances are 3.26-3.67 and 3.41Å, respectively. These carbon-carbon and Ag^+-Ag^+ distances are comparable to those observed in the infinite network systems described previously. In this complex, Ag^+-p interactions were not observed. Stang et al. reported that the angular bidentate ligands having 109.5° angles form pentagon, trigonal bipyramide, adamantanoid or cuboctahedron in self-assembly systems using Pd^<2+> and Pt^<2+> ions, and hexagonal macrocyclic systems need angular bidentate ligands having 120° angles. Less