Synthesis, Crystal Structure And Properties Of Coordination Polymers With Symmetric Schiff-base Ligands

The construction of coordination polymers via self-assembly of predesigned ligands with appropriate metal ions is a subject of current interest. These solid materials are attractive to chemists not only for the variety of topologies and intriguing frameworks, but also for their potential applications in catalysis, photochemistry, electrochromism, sorption, biology and medicine.The organic ligands containing nitrogen heterocyclic rings, such as pyridine and pyrazine, are excellent ligands and their coordination to metals leads to a variety of coordination complexes. Compared with the flexible ligands, the rigid ligands are particularly attractive for making expectant coordination polymer structures. Herein the chosen ligands, L¹ [bis(1-pyrazinylethylidene)hydrazine] and L² [(bis-(1-pyridin-4-yl-ethylidene)-hydrazine)], are easy-to-prepare and the two ligands are one of the shortest imine-based ligand systems. L¹ and L² are suitable to assemble different anion dependent coordination polymers with transition-metal ions. As part of our studies on the construction of metal-Schiff base species and POM-based compounds, in this paper we report the synthesis and characterization of ten interesting coordination polymers, including four 1D crystalline arrays, three 2D sheets and three 3D networks. The luminescent properties of L¹, L² and 1-10 in the solid were investigated.(1) Two 3D coordination polymers {[Ag₂L¹(NO₃)₂]·H₂O}_n (1), [Ag(L¹)0.5(SCN)]_n (2) and two 2D coordination polymers [L¹Cd(SCN)₂]_n (3), [L¹CdI₂]_n (4) have been synthesized and structurally characterized using ligand L¹.(2) One 3D coordination polymer {[CuL²(SCN)₂]CH3CN}_n (5),one 2D coordination polymer [CuL²2 (NO₃)₂·3H₂O]_n (6) and two 1D chains {[AgL²][AgL²NO₃](NO₃)(L²)_0.5(H₂O)₂}_n (7) and [ZnL²CL²]_n (8) have been synthesized and structurally characterized using ligand L².(3) Two 1D coordination polymers {[CuL²(DMF)3]2 (PW₁₂O₄₀)}_n[CuL²(DMF)₄]_n·nPW₁₂O₄₀·nDMF (9) and {[AgL²(DMF)]2(PMo₁₂O₄₀)]}_n[AgL²]_n·4nH₂O (10) have been synthesized and structurally characterized using ligand L² and saturated Keggin type polyoxoanions.