Synthesis And Characterization Of Novel Carboxylate Bridged Metal-organic Coordination Polymers

In resent years, much attention has been paid to the design, synthesis, crystal structures and properties of coordination polymers. And that the rational design and synthesis of novel metal-organic coordination polymers based on carboxylate ligands have attracted considerable interest. Carboxylate compounds have a good many coordination modes, such as: 1) monodentate, 2) chelating bidentate, 3) bidentate, 4) bridging monodentate, 5) chelating/ bridging multidentate, and have been extensively employed in the construction of a rich variety of high-dimensional structures. The supramolecular complexes have interesting topological structure as well as potential applications as catalysis, medicine, smart opto-electronic, magnetic and porous materials. It is essential to explore the synthesis, crystal structures of the complexes formed by the carboxylate ligand systematically, and to inquire into the factors that influence the formation and structures of the complexes containing carboxylate ligand. Not only can it lead to design and synthesize all kinds of functional materials, but also it may provide some reliable theoretical foundations for supramolecular chemistry and crystal engineering.In the present work, we used carboxylate acid, such as, aromatic polycarboxylate acid: 5-nitroisophthalic acid, 5-aminoisophthalic acid; N-heterocyclic polycarboxylate acid: imidazole-4,5-dicarboxylic acid, rare earth elements/ d¹⁰/ paramagnetic metal ions or the N-containing auxiliary ligands to construct series of novel metal-organic coordination polymers under hydro(solvo)thermal conditions. The structures and some properties of these compounds have been systematically investigated.The Schiff base ligands (H₃L) derived from the condensation of salicylaldehyde and its derivatives with simple peptides containing carboxylate groups, which is able to accommodate a copper(II) ion at the inner ONNO coordination site, leading to the mononuclear complexes [CuL]^-. We used H₃L (N-salicylideneglycylglycylglycine) with salicylaldehyde and its derivatives to get these mononuclear complexes which noteworthy that they contain unbridged carboxylate groups so that they can act as potential'ligands'to bind transition metal cation to give the heteropolymetallic complexes.Hydrothermal and volatilization methods were used to get single crystals of the complexes in this paper, in which mainly contains several parts as follow:1. The aromatic polycarboxylate acid: 5-nitroisophthalic acid used as carboxylate ligand with the introduction of N-containing auxiliary ligands, such as rigid pyridyl-based 4,4'-bpy, 1,10'-phen, highly flexible imidazole-based bbi. Herein, we report four interesting coordination polymeric complexes containing rare earth elements under hydro(solvo)thermal conditions. Compounds [La(O₂N-BDC)(O₂N-HBDC)(bbi)0.5]n(1) and [Gd(O₂N-BDC)(O₂N-HBDC)(4,4'-bpy)0.5]n (2) are both infinite two-dimensional layer structures which include carboxylate ligand, 5-nitroisophthalic acid and rare earth elements. Both bbi and 4,4'-bpy used as auxiliary ligands locate between two layers, which do not coordinate with rare earth elements. Compound [Yb2(O₂N-BDC)₃(phen)₂]_n (3) and compound {[Gd(O₂N-BDC)₃(phen)₂]2·0.5(CH₃OH)·0.5(H₂O)}_n (4) generate complicated 3D networks, however, P21/n space group for 3 and P1 space group for 4 are observed. Compared with the complexes of 3, complex 4 has the same ligands as it but has different coordination environment around the metal ion. So they display unidentical structure.2. Two compounds {[Ce₂(H₂N-BDC)₃(H₂O)₂]·1.75(H₂O)}_n (5) and {[Eu₂(H₂N-BDC)₃(H₂O)₂]₂·3(H₂O)}_n (6) are synthesized by direct hydrothermal reaction of 5-aminoisophthalic acid and appropriate lanthanide compound. 5-aminoisophthalic acid adopts many coordination modes, compounds 5 and 6 crystallized in the space group P1 and possessed isostructural 3D rhombic tunnel frameworks. The uncoordinated amino- group and water molecules are trapped in the pores. Compound 6 exhibits excellent blue fluorescence.3. Two coordination polymers contained d10 metal ions: Cd(II), [Cd(O₂N-BDC)(BIM)(H₂O)]_n (7), [Cd(HIDC)(bbi)_0.5]_n (8) have been hydrothermally synthesized from carboxylate compounds with the introduction of N-containing auxiliary ligands, such as rigid imidazole-based BIM, highly flexible imidazole-based bbi. Compound 7 contains unique one-dimensional double-chains, and these 1D chains form a 2D layer structure by hydrogen bonds. On the other hand, the Cd(II) ions in the 3D framework 8 exhibit hexahedral geometry. Each Cd(II) ions is firstly bridged through three HIDC^2- to form a 2D network. These 2D layers are further locked with bbi in bidentate fashion to lead to a complicated 3D porous framework. Compound 8 may be suitable as excellent candidate of blue fluorescent material, since it is highly thermally stable and insoluble in common solvents.4. Two coordination polymers possess two-dimensional layer structures: [Ba(O₂N-HBDC)2(H₂O)2]n (9), [Mn(H2N-BDC)(H₂O)·2H₂O]n (10) have been hydrothermally synthesized used aromatic polycarboxylate acid as bridged ligands. These 2D layers form 3D framework by significant hydrogen bonds andπ···πinteractions.5. Three copper (II) tripetitide Schiff base complexes: [Cd(H₂O)₂(CH₃OH)₂(CuL¹)₂]·2H₂O (11), [Cd(H₂O)₄(CuL²)₂]·2(CH₃OH)·2H₂O (12), [Co(H₂O)₄(CuL³)₂]·4H₂O (13), (H₃L¹=N-Salicylideneglycylglycylglycine, H3L2= N-3-methoxysalicylideneglycylglycylglycine, H₃L³= N-5-bromosalicylideneglycylglycylglycine) have been synthesized and structurally characterized. Single crystal X-ray diffraction analyses showed that the copper atom exhibits square-planar geometry, with the chelating ONNO atoms of the deprotonated Schiff base ligand(L) in the basal plane. In 11-13, two symmetric [CuL]^- groups coordination to M(II) (M=Cd, Co) at an inversion center, each via one carboxylate oxygen atom, to form a hetreotrinuclear complex.These complexes were characterized by elemental analysis, single-crystal X-ray crystallography, IR, UV-Vis, TG and fluorescence spectra.