Zinc(II) metal-organic frameworks with 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide: control of the parameters of the cationic porous framework and optical properties

Four zinc metal-organic frameworks (MOFs) with 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide (odabco) as a bridging ligand were synthesized by varying the solvent and the anionic composition of the reaction medium. The synthesis in a mixture of N, N-dimethylacetamide and water acidified with nitric acid affords the compound [Zn2(odabco)3(OAc)2](NO3)2(1) containing coordinated acetate anions. The compound [Zn2(μ-O)(odabco)3](NO3)2 · NMP · 2H2O (2) crystallizes in a mixture of N-methylpyrrolidone (NMP) and water in the presence of triethylamine as the base. The compound [Zn2(odabco)4](NO3)3(ClO4) · 2 DMF (3) was obtained in N,N-dimethylformamide (DMF) acidified with perchloric acid. The synthesis in a mixture of DMF and dioxane (dox) acidified with a larger amount of perchloric acid produces [Zn(odabco)2](NO3)(ClO4) · 0.4 dox (4). The crystal structures of new compounds 2–4 were determined by single-crystal X-ray diffraction. Compound 2 consists of binuclear {Zn2O}2+ units, serving as nodes in the three-dimensional framework with pcu topology and a solvent-accessible volume (Vpore) of 37%. The isomeric metal-organic coordination frameworks of 3 (Vpore = 42%) and 4 (Vpore = 47%) are built from mononuclear units and have a BCT zeolite topology. The optical absorption of compounds 1–4 was characterized by diffuse reflectance spectroscopy.