Self-Assembly of 2D→2D Interpenetrating Coordination Polymers Showing Polyrotaxane- and Polycatenane-like Motifs: Influence of Various Ligands on Topological Structural Diversity

A series of mixed-ligand coordination complexes, namely, [Cd2(bimb)2(L1)2] (1), [Cd(bpimb)0.5(L2)(H2O)] (2), [Zn5(bpib)2(L3)4(OH)2(H2O)2] (3), [Zn(bpib)0.5(L4)] (4), and [Cd(bib)(L4)] (5), where bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene, bpimb = 1,4-bis((2-(pyridin-2-yl)-1H-imidazol-1-yl)methyl)benzene, bpib = 1,4-bis(2-(pyridin-2-yl)-1H-imidazol-1-yl)butane, bib = 1,4-bis(1H-imidazol-1-yl)butane, H2L1 = 4-((4-(dihydroxymethyl)phenoxy)methyl)benzoic acid, H2L2 = 4,4′-methylenebis(oxy)dibenzoic acid, H2L3 = 3,3′-methylenebis(oxy)dibenzoic acid, and H2L4 = 4,4′-(2,2′-oxybis(ethane-2,1-diyl)bis(oxy))dibenzoic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. In 1, (L1)2− anions link the metal−neutral ligand subunits to generate a 2-fold parallel interpenetrating net with the 63 topology. In 2−4, neutral ligands connect the various metal−carboxylic ligand subunits to give a 2-fold parallel interpenetrating net with (4,4) topology in 2, a 2-fold parallel interpenetrating net with (3,6)-connected topology in 3, and a 3-fold parallel interpenetrating net with (4,4) topology in 4. Compounds 1−4 display both polyrotaxane and polycatenane characters. Compound 5 is a 5-fold parallel interpenetrating net with (4,4) topology. By careful inspection of these structures, we find that different topological structures showing both polyrotaxane and polycatenane characters have been achieved with increase of the carboxylic ligand length. It is believed that various carboxylic ligands and N-donor ligands with different coordination modes and conformations are important for the formation of the different structures. In addition, the luminescent properties of these compounds are discussed.