| Since A. Y. Liu and M. Cohen predicted in 1989 theoretically that the hardness ofβ-C3N4 (carbon nitride) might be harder than diamond, many researchers have showed a great interest in this potential material. Theoretical calculations indicated that carbon nitride might have a few phases and possess a variety of interesting physical properties. Tremendous efforts have been investigated to synthesize carbon nitride so far. However, to our knowledge, there have been no convincing results. According to theoretical calculations, building block of carbon nitride is triazine or heptazine. There are quite a few studies on triazine or heptazine and their derivatives. These investigations not only offer the science communities to understand the structures and properties of building blocks, but may also help them find suitable routes, e.g. via precursors, to prepare carbon nitride. The contents of the present thesis are the synthesis and structure characterizations of some new derivatives of triazine and heptazine.The product obtained via the solid state reaction of melamine and ammonium chloride was dissolved under hydrothermal conditions in dilute hydrochloric acid, hydrobromic acid and nitric acid, respectively. Colorless crystalline compounds were obtained after evaporation of the solutions. Single crystal structure analyses show that chemical formulas of the compounds are C3H5N5OCl, C3H5OBr and C3H5N5ONO3, respectively.All the three crystal structures belong to the monoclinic system with P2(1)/c space group. There are four molecules in each unit cell. The unit cell parameters are as follows: C3H5N5OCl: a = 5.356(5) (?), b = 14.646(5) (?), c = 8.119(5) (?),β= 90.028(5)°, V= 636.9(7) (?)3; C3H5N5OBr: a = 5.257(5) (?), b = 8.834(5) (?), c = 14.663(5) (?),β= 98.283°, V = 673.9(8) (?)3; C3H5N5ONO3: a = 9.318(5) (?), b = 6.347(5) (?), c = 13.537(5) (?),β= 108.147(5)°, V = 760.8(8) (?)3. In the crystals, Mono-protonated triazine cations are the basic structure unit. They form layers or strands of cations via hydrogen bonds.By dissolving the white pyrolysis product of melamine in dilute sulfuric acid under hydrothermal conditions, colorless crystals were obtained after condensing the solution. The chemical formula of the crystalline compound is C3N6H8SO4. The crystal structure belongs to monoclinic system with C2/c space group. There are eight molecules in one unit cell (Z = 8). The unit cell parameters of this crystal structure are: a = 18.5787(3) (?), b = 8.6272(2) (?), c = 12.7945(4) (?),β= 129.739°, V = 1576.94(7) (?)3.In the crystal structure, two diprotonated melamine cations are connected via N-H...N hydrogen bonds forming into [(C3H8N6)2]4+ dimers. The two melaminium cations of one dimer are in the same plane. Each [(C3H8N6)2]4+ dimer is surrounded by ten sulfate anions, which connect the melaminium dimers with adjacent melaminium cations via N-H...O hydrogen bonds, forming two-dimensional layers. Three-dimensional supramolecular framework is constructed by stacking the layers via multiple hydrogen bonds and n-n interactions.From the hydrochloric and perchloric solution in an autoclave of the yellow pyrolysis product of melamine , colorless crystalline compounds were obtained after evaporation of the solvents. The chemical formulas of the compounds are C6N10H8SO4·2H2O and C6N10H7ClO4·H2O, respectively. Another colorless crystalline compound was obtained after the yellow product was treated under hydrothermal conditions in an autoclave. The chemical formula of the compound is C6N10H6·H2O.The structure parameters of the above three crystals are: C6N10HNio8SO4·2H2O: monoclinic, P2(1)/n, a = 6.903(5) (?), b = 20.237(5) (?), c = 9.617(5),β= 90.028(5)°, V = 1327.1(12) (?)3. Z = 4; C6N10H7ClO4·H2O: triclinic, P-1, a = 7.265(5) (?), b = 7.577(5) (?), c = 12.071(5) (?),α= 71.747(5)°,β= 90.028(5)°,γ= 71.072(5)°, V = 590.2(6) (?)3, Z = 2; C6N10H6·H2O: trigonal, R-3c, a = 28.796(5) (?), b = 28.796(5) (?), c = 6.736(5) (?), V = 4837(4) (?)3, Z = 18.In the crystal structures of C6N10H8SO4·2H2O and C6N10H7ClO4·H2O, protonated heptazine C6N10H82+ and C6N10H7+ are the counterions of SO42- and ClO4-, respectively. The heptazine cations are connected via hydrogen bonds, forming two dimensional layers. Strong hydrogen bonds and n-n interactions between the layers render the crystal structures with the feature of three-dimensional frameworks. In the crystal structure of C6N10H6H2O, there are two holes in one unit cell and each of them is built up by six C6N10H6 molecules connected by N-H-N hydrogen bonds. Water molecules are filled in the holes.Under hydrothermal conditions, the reactions of melamine and triazine chloride with corresponding metal salts produced three metal-cyanurate complexes. Their chemical formulas are C3H2N3O3Na·H2O, (C3H2N3O3)2Cu(NH3)2 and (C3H2N3O3)4Ag2·H2O, respectively.Both C3H2N3O3Na·H2O and (C3H2N3O3)2Cu(NH3)2 belong to triclinic system with P-1 space group. There are two molecules in one unit cell each. Their unit cell parameters are as follows: C3H2N3O3Na·H2O: a = 3.5987(1) (?), b = 9.1257(1) (?), c = 9.2311(1) (?),α= 91.139(1)°,β= 99.159(1)°,γ= 91.535(1)°, V = 299.093(1) (?)3; (C3H2N3O3)2Cu(NH3)2: a = 5.044(5) (?), b = 6.998(5) (?), c = 9.112(5) (?),α= 90.271(5)°,β= 98.083(5)°,γ= 110.837(5)°, V = 297.1(4) (?)3.The crystal structure of (C3H2N3O3)4Ag2·H2O belongs to orthorhombic system with Fddd space group. The unit cell parameters are a = 9.6265(7) (?), b = 12.5004(8) (?), c = 37.097(3) (?), V = 4464.1(5) (?)3, Z = 8.Besides Na-O ionic bond interactions, there are hydrogen bonds andπ-πinteractions in the crystal structure of C3H2N3O3Na·H2O. In the crystal structure of (C3H2N3O3)2Cu·(NH3)2, each Cu2+ cation is coordinated by two C3H2N3O3- anions linearly. The complex molecules are connected via the intermolecular N-H...O hydrogen bonds forming holes. In the crystal structure of (C3H2N3O3)4Ag2·H2O, the cyanurate anions are linked by coordination bonds and intermolecular hydrogen bonds, forming 2D sheets which are perpendicular to b axis. These sheets are further linked to form infinite 3D coordination framework by Ag...Ag interactions, intermolecular offset n-n stacking interactions and weak hydrogen bonds. Photoluminescence and thermogravimetric analyses indicate that (C3H2N3O3)2Cu·(NH3)2 and (C3H2N3O3)4Ag2·H2O are thermally stable luminescent materials.
|
PDF Full Text Request