The Synthesis And Structure Of Transitional Metal–pyridinecarboxylic Coordination Polymers

Coordination polymers have attracted much attention for the charming tailor-made structure and the potential applications in the fields of catalysis, adsorption, magnetics and second-order nonlinear optics etc. Rigid carboxylic ligands have been widely used to design and construct metal-organic framework (MOF) coordination polymers becasue their anionic nature can provide charge balance and covalent interactions with metal salt forming scaffold coordination polymer networks. The carboxylate derivertives of pyridine, multifunctional ligands containing N- or O-donors, have usually been used to bind metal centers to form metal-organic framework (MOF) coordination polymers. Nicotinic acid is an essential vitamin in the body of human being. Nicotinic acid can translate into nicotinamide, which is the important part of coenzyme I and II. Along with the asymmetric structure, the design and synthesis of transitional metal-nicotinic acid coordination polymers are in favor of the possibility of forming novel topological structure with non-linear optical properties and the significant value of simulated enzyme. Here, the synthesis of a series of coordination polymers construced from transitional metals and nicotinic acid/3,5-pyridinedicarboxylic acid. The single-crystal structures of the coordination polymers were determined by single-crystal X-ray diffraction, and the purity, composition and stability were also investigated through XRD ,FT-IR and TGA.1. Cadmium-nicotinic coordination polymers: Cd(IN)(DMF)(H₂O)(NO₃) (1), Cd(IN)₂(H₂O)·DMF (2) and Cd2(H₂O)(IN)₄·DMF (3) were synthesized using Cd(NO₃)₂·4H₂O in the organic solvent mixture of DMF and ethanol/acetonitrile through solvent evaporation. The X-ray crystallography show that compound 1 is a 1D chain, the structure are connected by O-H…O hydrogen bonds, forming three-dimensinal supramolecular frameworks. Both compounds 2 and 3 are 3D networks.In compound (2), two nicotinic ligands connected to two Cd(II) to form a 2D layer in the ac plane .And another two nicotinic ligands link the 2D layer in the b axis, forming the 3D structures. Compound (3) exhibit 3D structure based on Cd2(H₂O)(IN)₄ building blocks and posses open channels that are occupied by removable solvent DMF molecules.2. Transitional metals-nicotinic coordination polymers: Zn(IN)₂ (4), Cu(IN)Cl (5) and Mn₂(H₂O)(IN)₄·DMF (6) were synthesized using Zn(NO₃)₂·6H₂O,Cu(NO₃)₂·3H₂O and MnCl₂·4H₂O as metal salts, respectively. Zn(IN)₂ (4) is 2D layered network ,and has left-hand and right-hand chrial chains in the layers.Cu(IN)Cl (5) is a zero dimension structure, the structure are connected byO-H…O andC-H…Cl hydrogen bonds, forming three-dimensinal supramolecular frameworks. Compound (6) exhibit 3D structure based on Mn₂(H₂O)(IN)₄ building blocks and posses open channels that are occupied by removable solvent DMF molecules.3.Nickle-3,5-pyridinedicarboxylate coordination polymers: Three coordination polymers [Ni(3,5-Pydc)(H₂O)₄·H₂O]_n (7), [Ni2(3,5-pydc)₂(H₂O)₈·(H₂O)₂]_n (8) and [Ni(3,5-pydc) (H₂O)₂]_n (9) were synthesized using NiCl₂·6H₂O as metal salt through hydrothermal method. X-ray crystallography reveals that both compound (7) and (8) are 1D zigzag chains, while compund (9) is a 2D layered network. In compound (7), 3,5-Pydc ligand links two different Ni(II) into 1D zigzag chain. There are two independent 1D zigzag chains with same coordination mode in compound (8) and each zigzag chain is formed by 3,5-Pydc ligand connecting with Ni(II). Compound (9) is a 2D network constructed by twenty-membered rings comprising three Ni(II) and three 3,5-Pydc ligands. Furthermore, three compounds form 3D supramolecular frameworks through O-H…O hydrogen bonds among chains or layers. The guest water molecules are defined in supramolecular frameworks of compound (7) and (8).