Metal-Organic Frameworks Based on Unprecedented Trinuclear and Pentanuclear Metal-Tetrazole Clusters as Secondary Building Units

Abstract

Solvotherrnal reactions of manganese(II) chloride tetrahydrate with a bis-tetrazole ligand, 2,6-di( 1H-tetrazol-5-yl)naphthalene (H2NDT), in N,N'-dimethylforrnamide (DMF)/MeOH mixed solvent at two slightly different temperatures, 75 and 100 degrees C, led to two different metal-organic frameworks (MOFs), [(Mn3O)-O-II(HNDT)(2)(NDT)(DMF)(3)] (1) and [(Mn5O2)-O-II(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, [(Mn3O)-O-II(CN4)(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/NDT2- deprotonation states is a linker, where two tetrazole (CN4) groups of the ligand are connected via a rigid naphthyl group. The tetrazole groups in 1 adopt a 1,2-mu-bridging mode with the manganese(111) ions to form a mu(3)-oxo trinuclear SBU. The trigonal prismatic 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, [MnII5O2(CN4)(8)], as an 8-connected tetragonal prismatic SBU of topological D-4h site symmetry. The tetrazole groups in 2 adopt monodentate, 1,2-mu- and 2,3-mu-bridging bidentate and 1,2,3-mu-bridging tridentate binding modes with the manganese(II) centers to form a bis-mu(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.