Modulated preparation and structural diversification of Zn-II and Cd-II metal-organic frameworks with a versatile building block 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol

摘要

Four novel Zn-II and Cd-II metal-organic coordination polymers with a versatile building block 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (Hpyt) have been prepared under different conditions. [Zn-3(pyt)(4)(OH)(2)](n) (1) and [Cd(pyt)(HCOO)](n) (3) were obtained through a solvothermal method, whereas {[Zn(pyt)(2)(H2O)(2)].(DMF)(2)}(n) (2) and {[Cd(pyt)(2)].CHCl3}(n) (4) were isolated under general conditions. X-ray single-crystal diffraction indicates that the anionic ligand pyt adopts a thioamide isomer in 1, 2, and 4, but a thiolate form in 3. Four types of binding modes involving monodentate (eta-N-oxa), bidentate (mu-N-py, N-oxa, or mu-N-py,S,S) and tridentate (mu-N-py, N-oxa, S) are observed. The discrepancy of the synthetic routes and metal-coordination preferences facilitates the production of the final crystalline materials with distinct network structures, including a 1D zigzag array of 1 with dangling arms, a common 2D ( 4,4) coordination layer of 2, a decorated 3D alpha-Po network of 3, and an unprecedented (3,6)- connected 3D framework of 4 with a (4(2).6)(2)(4(2).6(2).8(7).10(2)) topology. Notably, the hydrolysis of DMF solvates leads to the formation of formate ions, being a component in the structure of 3. Complexes 2 and 4 show 1D channels in which the solvates are accommodated, and even after the exclusion of these guests, the porous host frameworks are still retained. Thermal stability and gas adsorption properties have also been studied.