Synthesis and characterization of new coordination polymers generated from oxadiazole-containing ligands and IIB metal ions

The coordination chemistry of the oxadiazole-containing rigid bidentate ligands 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (L1) and 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L2) with inorganic IIB metal salts have been investigated. Five new coordination polymers (1-5) were prepared by solution reactions and fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Cd(L1)₂(CH₃CN)₂](ClO₄)₂ · (CH₃CN)₂ (1) crystallized in the monoclinic space group P2₁/c, a = 8.4028(5) Å, b = 21.3726(13) Å, c = 10.5617(7) Å, β = 95.1200(10)°, and Z = 2. In the solid state, it adopts an infinite two-dimensional polymeric structural motif with effective cross section of ca. 14.31 × 14.31 Å. Cd(L2)(H₂O)(NO₃)₂ (2) crystallized in the monoclinic space group Ia, a = 7.1203(5) Å, b = 22.2475(15) Å, c = 20.2652(16) Å, β = 90.6080(10)°, and Z = 8. In the solid state, the two Cd(II) centers are connected to each other by L2 ligands and bridging nitrates into a two-dimensional network. ZnCl₂(L1)] (3) and HgI₂(L1)] · CH₃CN (4) crystallized in the monoclinic crystal system (3: P2₁/c, a = 5.3702(3) Å, b = 20.4800(11) Å, c = 12.4093(7) Å, β = 94.7930(10)°, and Z = 4; 4: P2/n, a = 17.2733(11) Å, b = 5.2173(3) Å, c = 20.4069(13) Å, β = 102.8690(10)°, and Z = 4). In the solid state, Zn(II) and Hg(II) metal centers are connected to each other by L1 ligands into a zigzag chain motif. Compound 5 (HgBr₂(L2) is different from 3 and 4, monoclinic, P2(1)/n, a = 5.470(4) Å, b = 16.271(13) Å, c = 16.486(12) Å, β = 93.197(15)°, and Z = 4) adopts a novel one-dimensional helical chain motif which resulted from the relative different coordinated orientation of the two N-donors on L2 ligand.