A series of metal–organic frameworks containing diverse secondary building units derived from a flexible triazine-based tetracarboxylic ligand

Abstract

Five new coordination polymers, {[Zn₂(CCTA)(DMF)₂]·(DMF)·(H₂O)₂}_n (1), {[Zn_2.5(CCTA)(OH)(H₂O)]·(DMF)·(H₂O)}_n (2), {[Zn₂(CCTA)(H₂O)₃]·(NMP)₂·(H₂O)₃}_n (3), {[Cd₄(CCTA)₂(DMF)₄(H₂O)₂]·(H₂O)₆}_n (4) and {[Cd₄(CCTA)₂(H₂O)₄]·(H₂O)₄}_n (5), (H₄CCTA = 2,4-bis(4-carboxyphenylamino)-6-bis(carboxymethyl)amino-1,3,5-triazine, DMF = N,N′-dimethylformamide, NMP = N-methyl-2-pyrrolidone), have been solvothermally synthesized and contain diverse secondary building units (SBUs). Due to various coordination modes and different conformations of the flexible H₄CCTA ligand, the five complexes exhibit different topologies. Complex 1 has a two-dimensional (2D) structure with (4,4)-sql topology constructed with tetranuclear zinc clusters. Complex 2 also possesses a 2D framework with an unprecedented (4¹⁸·6¹⁰)(4⁵·6)₂ point symbol based on pentanuclear zinc clusters. Complex 3 shows a three-dimensional (3D) framework with PtS topology, containing linear tetranuclear zinc clusters. Both complexes 4 and 5 with 3D frameworks are built with rare infinite Cd–O–Cd and Cd₂O₂ rod-shaped SBUs, respectively. Furthermore, complex 4 could be described as a 4-connected uninodal umc net, instead of the pillared-layer structure of complex 5.