Metal-organic frameworks based on unprecedented trinuclear and pentanuclear metal-tetrazole clusters as secondary building units

摘要

Solvothermal reactions of manganese(II) chloride tetrahydrate with a bis-tetrazole ligand, 2,6-di(1H-tetrazol-5-yl)naphthalene (H_2NDT), in N,N′-dimethylformamide (DMF)/MeOH mixed solvent at two slightly different temperatures, 75 and 100 °C, led to two different metal-organic frameworks (MOFs), [Mn_3~(II)O(HNDT)_2(NDT)(DMF)_3] (1) and [Mn_5~(II)O_2(HNDT)_2(NDT) _2(DMF)_8] (2), with different net topologies. Single-crystal X-ray diffraction studies reveal that 1 is constructed from an unprecedented trinuclear building block, [Mn_3~(II)O(CN _4)_6], as a 6-connected trigonal prismatic secondary building unit (SBU) of topological D_(3h) site symmetry, and that the ligand in the HNDT~(-1)/NDT~(2-) deprotonation states is a linker, where two tetrazole (CN_4) groups of the ligand are connected via a rigid naphthyl group. The tetrazole groups in 1 adopt a 1,2-μ-bridging mode with the manganese(II) ions to form a μ~3-oxo trinuclear SBU. The trigonalprismatic SBU in 1 is connected to six neighboring SBUs to form a three-dimensional MOF of acs net topology. 2 is constructed from an unprecedented pentanuclear building block, [Mn_5~(II)O _2(CN_4)_8], as an 8-connected tetragonal prismatic SBU of topological D_(4h) site symmetry. The tetrazole groups in 2 adopt monodentate, 1,2-μ- and 2,3-μ-bridging bidentate and 1,2,3-μ-bridging tridentate binding modes with the manganese(II) centers to form a bis-μ_3-oxo pentanuclear SBU of local C_2 site symmetry. The tetragonal prismatic SBU in 2 is connected to eight neighboring SBUs to form a 3-D MOF of bcu net topology.