| Nitrogen-containing six-membered heterocyclic carboxylic acid is a kind of polydentate organic ligand containing N and O atoms simultaneously, which can connect all kinds of metal ions to form mononuclear, polynuclear, one-dimensional, two-dimensional or three-dimensional coordination polymers or supramolecular compounds with multi functions. In addition to novel structural topology, this kind of complex has potential application in functional materials and molecular recognition. In this thesis the studies on the nitrogen-containing six-membered heterocyclic carboxylate complexes are reviewed. We report here nine compounds using 2, 4-dihydroxypyrimidine-5-carboxylic acid (H3iso) as ligands, which were prepared by hydrothermal method and characterized by IR, elemental analysis and single crystal X-ray diffraction analysis. The thermogravimetric and luminescent properties of some of these compounds were also studied.The 2,4-dihydroxypyrimidine-5-carboxylic acid (H3iso) ligand in this work presents several coordination modes as shown below.Main work is listed below:1. A monoclinic complex [Co(H2iso)2(H2O)2] (1) and a 2-D coordination polymer [Mn(Hiso)(H2O)2]n (2) were synthesized from the hydrothermal reactions of cobalt(II) and manganese salts with 2, 4-dihydroxypyrimidine-5-carboxylic acid, which were characterized by IR,elemental analysis and single crystal X-ray diffraction analysis. It was shown that complex (1) crystallizes in the monoclinic space group P21/n with a = 5.0608(6), b = 15.0873(17), c = 9.2899(10) ?,β=99.3890(10)? and complex (2) crystallizes in the orthorhombic space group Pbca with a = 12.9325(17), b =6.7317(9), c = 17.018(2) ?. The ligand in complex (1) coordinates to the Co(II) ion in coordination mode (a). The Co(II) ion is six-coordinated in a distorted octahedral geometry. Intermolecular hydrogen bonds in complex (1) help to construct a three dimensional supramolecular framework. The TGA of complex (1) agrees well with the crystal structure. The ligand in complex (2) adopts a coordination mode (b). The Mn(II) ion in complex (2) is six-coordinated in a distorted octahedral geometry. Two Mn(II) ions in complex (2) are bridged by two hydroxyl groups from two Hiso2- ions constructing a centrosymmetric dinuclear building block which are further connected to another four dinuclear building blocks by the bridging of the ligand to construct a two dimensional framework. Theπ-πinteractions and hydrongen bonds further stabilize the two-dimensional network. Other hydrogen bonds extend two dimensional sheets into a three dimensional supramolecular framework.2. The hydrothermal reaction of lead chloride with 2,4-dihydroxypyrimidine-5-carboxylic acid gave a 2D coordination polymer [Pb(Hiso)(H2O)]n (3) which was characterized by IR, elemental analysis and single crystal X-ray diffraction analysis. It was shown that complex (3) crystallizes in the monoclinic space group P21/n with a = 6.9924(14) ?, b = 16.463(3) ?, c = 6.5308(13) ?,β= 111.81(3)?. The ligand in complex (3) adopts a coordination mode (c). The Pb(II) ion is five-coordinated in a distorted square pyramid geometry. The intermolecular hydrogen bonds andπ-πstacking interactions in complex (3) help to build a three dimensional supramolecular framework. The band in the emission spectrum of complex (3) might be assigned to a S→P transition in Pb(II) ion.3. The hydrothermal reaction of rare-earth salts with 2, 4-dihydroxypyrimidine-5-carboxylic acid and phen produced five mononuclear complexes [RE(Hiso)(H2iso)(phen)2]·2H2O [RE = Y (4), Sm (6), Gd(7), Dy (8) and Er (9)] and a dinuclear complex [Nd2(Hiso)(H2iso)4(phen)2- (H2O)2]·6H2O (5), which were characterized by IR, elemental analysis and single crystal X-ray diffraction analysis. Complexes (4), (6), (7), (8) and (9) have similar structure and crystallize in the monoclinic space group C2/c with a = 17.1740(13), b = 14.4385(11), c = 13.2365(10),β=100.8810(10)? for (4); a = 17.128(3), b= 14.528(3), c =13.146(3),β= 99.13(3)? for (6); a = 17.158(8), b = 14.504(7), c = 13.197(7),β=99.955(5)? for (7); a = 17.143(2), b = 14.4470(17), c = 13.2211(16),β=100.613(2)? for (8);and a = 17.1602(7), b=14.4170(6), c = 13.2433(5),β= 101.159(1)? for (9). Complex (5) crystallizes in the triclinic space group P1 with a = 10.1980(7) ?, b = 12.8896(9) ?, c =13.3383(9) ?,α= 118.7110(1)°,β= 90.010(1)°,γ= 108.6120(1)°. The ligand in complex (4), (6), (7), (8) and (9) adopts a coordination mode (a). The RE (III) ions are eight-coordinated in distorted square antiprism. The carboxylates of Hiso2- and H2iso- anions adopt unidentate coordination mode. Hydrogen bonds further extend complexes (4), (6), (7), (8) and (9) into three dimensional supramolecular frameworks. The ligand in complex (5) coordinates to Nd(III) ion via coordination modes (a) and (d). Two Nd(III) ions are nine-coordinated in distorted monocapped square antiprismatic geometries. The Hiso2- anion bridges two Nd(III) ions. The carboxylato groups of Hiso2- and H2iso- anions adopt unidentate coordination modes. Hydrogen bonds further extend complex (5) into a three dimensional supramolecular network. Luminescent studies on (6) and (8) show that the ligand 2,4-dihydroxypyrimidine-5-carboxylicacid and phen can act as an"antenna"to sensitize the fluorescence of lanthanide metal centers. The TGA of complex (4)～(6),(8),(9) are well agreed with the crystal structures. |
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