Assemblies of Two Mixed-Ligand Coordination Polymers with Two-Dimensional Metal−Organic Frameworks Constructed from M(II) Ions with Croconate and 1,2-Bis-(4-pyridyl)ethylene (M = Cd and Zn)

Abstract

Two metal−croconate (C5O52-) complexes, {[Cd2(bpe)(C5O5)2(H2O)]·2H2O}n (1) and {[Zn2(bpe)2(C5O5)2]}·H2O}n (2) (bpe = 1,2-bis(4-pyridyl)ethylene)) with two-dimensional (2-D) metal−organic frameworks (MOFs), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction studies. Structural determination reveals that compound 1 possesses a 2-D layered MOF with two rectangular boxes as the basic building units through the connectivity of CdII with μ3-croconates, μ5-croconates, and bpe ligands. In compound 2, a 2-D brick-wall-like layered framework is formed by using a rectangular grid as the basic building unit through the connectivity of ZnII with hybrid μ3-croconates, μ4-croconates, and bpe ligands. Two layers are then cross-linked by the other bpe ligands to complete a 2-D bilayered MOF. Both of the 2-D MOFs are extended to three-dimensional supramolecular architectures through π−π and C−H···O interactions between the croconate and the pyridyl rings of bpe, which exhibit high thermal stability and retain their crystalline forms up to 350 °C.