2D and 3D Cadmium(II) Coordination Polymers from a Flexible Tripodal Ligand of 1,3,5-Tris(carboxymethoxy)benzene and Bidentate Pyridyl-Containing Ligands with Three-, Eight- and Ten-Connected Topologies

Abstract

Four novel cadmium(II) coordination polymers, [Cd3(TCMB)2(4,4-bipy)(H2O)16]n (1), [Cd3(TCMB)2(bpe)(H2O)13]n (2), [Cd3(TCMB)2(bpe)2(H2O)4]n (3), and [Cd3(TCMB)2(dpp)2(H2O)3]n (4), [TCMB = 1,3,5-tris(carboxymethoxy)benzene, 4,4-bipy = (4,4-bipyridine), bpe = 1,2-bis(4-pyridyl)ethane, dpp = 1,3-bis(4-pyridyl)propane] have been hydrothermally synthesized by the self-assembly of the flexible tripodal acid TCMB and Cd(OAc)2·2H2O with pyridyl-containing ligands possessing different flexibilities. Single-crystal X-ray diffraction analysis reveals that the four polymers exhibit novel frameworks due to diverse coordination modes and different conformations of the flexible TCMB as well as pyridyl-containing ligands. Complex 1 shows a unique twofold parallel interpenetrating 2D honeycomb network structure with an unusual 63 topology, in which two different large hexagonal rings are arranged alternately, with extraordinarydimensions of ca. 22.172(6) × 12.947(2) Å (A) and 17.233(2) × 12.947(2) Å (B) based on the distances of the atoms at the opposite positions of the rings. Complex 2 is almost isostructural to complex 1, except that the bidentate bpe ligands bridge the cadmium centers in an anti conformation, rendering the network more flexible. Complex 3 features a 3D network with one of the scarce eight-connected (46, 614, 88)(43)2 topologies based on the rare CdI2-type layer constructed from secondary building units (SBUs) of rare [Cd3(CO2)4]2- isosceles triangle cadmium clusters. Complex 4 possesses distorted CdI2-type layers constructed from unprecedented ten-connected Cd3 clusters which are linked by more flexible dpp ligands in a trans-gauche (TG) conformation in (4,4) networks, leading to another 3D framework of the unusual (418, 624, 83)(43)2 topology. Such an arrangement represents the highest connected topology presently known for the frameworks. Among them, complex 1 displays photoluminescent properties at 460 nm due to the ligand-to-metal charge transfer (LMCT).