Crystal Structures and Spectroscopic Properties of Metal-Organic Frameworks Based on Rigid Ligands with Flexible Functional Groups

Two rigid linear ligands with alkoxy functional groups (L1 = 4,4'-(2,5-dimethoxy-1,4-phenylene) dipyridine; L2 = 4,4'-(2,5-diethoxy-1,4-phenylene) dipyridine) incorporating carboxyl-containing auxiliary ligands (isophthalic acid = H(2)IPA; terephthalic acid = H(2)TPA; biphenyl-4,4'-dicarboxylate = H2BPDC) have been adopted to build a series of complexes with M(II) (M = Zn, Co, Cd) under solvothermal conditions. The formula of these complexes are {[Zn(L1)(IPA)]}(n) (1), {[Zn(L1)(TPA)]center dot DMF}(n) (2), ([Co(L1)(TPA)(H2O)(2)]center dot 2DMF}(n) (3), {[Cd(L1)(TPA)(H2O)(2)]center dot 2DMF}(n) (4), and {[Co(L2)(BPDC)]center dot 0.5H(2)O}(n) (5). Five complexes have been characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction and thermogravimetry measurements. Topological analyses reveal that complex 2 is a 6-connected pcu net with point symbol {4(12).6(3)}, while complex 5 is a 6-connected rob net with point symbol {4(8).6(8).8}, the other complexes 1, 3, and 4 can be simplified as 4-connected sq1 nets with point symbol {4(4).6(2)}. Complexes 1, 3, and 4 are 2D layer motifs, 2 and 5 are both 2-fold interpenetrating 3D frameworks. The optical absorption spectra of 3 and 5 indicate the nature of semiconductivity. The strong fluorescence emissions and long emission lifetimes of 1, 2, and 4 display that they are promising phosphorescent materials.