The Syntheses, Structures And Properties Of Complexes Based On Pyridine Carboxylic Ligand

The Metal-organic-frameworks, due to their diverse structures and potentialapplications, have become one of the hot research fields. Among these influentialfactors upon the syntheses of metal-organic-frameworks, the judicious selections oforganic ligands play an indispensable role in the construction and structural diversityof coordination polymers. Recent decade, bifunctional pridine-carboxylate ligandshave captured the chemistry’s attention, because they possess N-and O-potentialelectron-donating centers which can exhibit diverse coordination modes with metalcenters and various structures.In this paper, twelve complexes based on a new type of pridine-carboxylate ligand3,3’-(pyridine-3,5-diyl)dibenzoic acid (H2pddb) have been synthesized undersolvothermal condition. The main contents are summarized as follows:1. Varying pH values, five Zn/Cd/Mn complexes,[Zn(pddb)(H2O)]n(1),[Zn(pddb)]n(2),{[Cd2(pddb)2]·H2O}n(3),[Cd(pddb)(H2O)2]n(4) and {[Mn2(pddb)2]·H2O}n(5), have been synthesized by the reaction with transition metal salts undersolvothermal condition. Complex1shows a binodal3,3-connected wavelike layerstructure with the point symbol of (63)2. However,2performs a binodal3,6-connected3D coordination framework with the point symbol of(4·62)·(42·68·85).3exhibits a more complicated3D periodic structure built on aninfinite rod-shape secondary blocking units (SBUs), while4shows a double-chainstructure, extended into3D supramolecular framework through strong hydrogenbonding interactions. The1D chain-shape SBUs link with the skeleton of H2pddb,to generate the3D framework of complex5. The studies about the elementalanalyses, IR, TGA, fluorescence properties of the complexes14and themagnetism of complex5have also been characterized.2. Four microporous coordination polymers {[Co2(pddb)2(H2O)3]·(DMA)2·(H2O)6}n(6),{[Ni2(pddb)2(H2O)3]·0.5DMA·2H2O}n(7),{[Co2(pddb)2(H2O)3]·DMF·4H2O}n(8),{[Co2(pddb)2(DMF)(H2O)2]n(9), have been obtained by the reaction of H2pddb and transition metal Co2+, Ni2+salts. These three complexes containsimilar Co2(COO)2units to construct3D structures, but complex7have distinctstructure from the other two due to the coordination of DMF to metal centers.From the view of topologies, the point symbols of the complexes68are(42·6)·(44·62·88·10), while that of9is (4·62)2·(42·610·83). In addition, the XRD, IR,elemental analyses and TGA of the complexes68were studied.3. In the presence of a N donor ligand1,4-bis(1,2,4-triazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (btmx), threecomplexes [Cd(pddb)(btmx)]n10and [Co2(pddb)2(btmx)0.5]n11,[Ni(pddb)(btmx)]n12, have been synthesized by using H2pddb and Cd, Co salts.The structure analyses indicate that10and12are heterogeneous isomorphismand perform a binodal (3,5)-connected3D coordination framework with the pointsymbol of (42·65·83)·(42·6). Btmx link with the step-like chain which is constructedby the pddb2-ligand and Co centers to result into the2D layer structure of11. Inaddition, the elemental analyses, IR, XRD, TGA and photoluminescence of thecomplex10were studied.