Two ZnII Metal-Organic Frameworks with Coordinatively Unsaturated Metal Sites: Structures, Adsorption, and Catalysis

Assembly of Zn(NO3)2 with the tripodal ligand H3TCPB (1,3,5-tri(4-carboxyphenoxy)benzene) affords two porous isoreticular metal-organic frameworks, [Zn3(TCPB)2 center dot 2DEF]center dot 3DEF (1) and [Zn3(TCPB)2 center dot 2H2O]center dot 2H2O center dot 4DMF (2). Single-crystal X-ray diffraction analyses reveal that 1 crystallizes in the monoclinic space group P21/c and possesses a 2D network containing 1D microporous opening channels with an effective size of 3.0x2.9 angstrom 2, whereas 2 crystallizes in the trigonal space group P (3) over bar c1 and also possesses a 2D network containing 1D channels, with an effective aperture of 4.0x4.0 angstrom 2. TOPOS analysis reveals that both 1 and 2 have a (3,6)-connected network topology with the Schlafli symbol of (43.612) (43)2. According to the variable-temperature powder X-ray diffraction patterns, the solid phase of 1 can be converted into that of 2 during a temperature-induced dynamic structural transformation, thus indicating that the framework of 2 represents the most thermally stable polymorph. Desolvated 2 exhibits highly selective adsorption behaviors toward H2/N2, CO2/N2, and CO2/CH4; furthermore, it displays size-selective catalytic activity towards carbonyl cyanosilylation and Henry (nitroaldol) reactions.