Coordination polymers with the angular dipyridyl ligand 1,3,4-thiadiazole-2,5-di-3-pyridyl: Influence of analogue dipyridyl ligands and bridging anions on structural diversity

The self-assembly of Zn-II, Cd-II, and Cu-II salts with the angular ligand 1,3,4-thiadiazole-2,5-di-3-pyridyl (L-1) and three secondary ligands, 1,3-di-4-pyridylpropane (L-2), 4,4'-dipyridyl (L-3), and 2,3-dimethylpyrazine (L-4), produced six new one- and two-dimensional coordination polymers. The unusual two-dimensional bilayer coordination polymer [Zn(L-1)(SO4)](n) (1) obtained from L-1, L-3 (or L-4), and ZnSO4 center dot 7H(2)O has SO42--bridged chiral inorganic 1-D ladders that are wound by L-1 from two unparallel directions to form a novel chiral channel structure. According to the same synthetic procedure of 1, only the displacement of L 3 (or L-4) with L-2. however, afforded the one-dimensional coordination polymer {[Zn(L-1)(2)(H2O)(SO4)](H2O)(2)}(n) (2). Interestingly, the elegant dipyridyl ligands L-2, L-3, and L-4, unlike their analogue L-1 coordinating to metal ions, affect the structural configuration of the resulting single crystals, even though they do not exist in these compounds. Another 2-D bilayer coordination polymer, [Cd(L-1)(H2O)(SO4)](n) (3), synthesized from L-1 and CdSO4 center dot 7H(2)O, however, has a different framework from 1. By contrast, the replacement of a bridging SO42- anion in 3 by a SCN- anion results in a 2-D monolayer coordination polymer [Cd-2(L-1)(3)(SCN)(4)](n) (4) with the grid network. Furthermore, the 1-D zigzig coordination polymer [Cu-2(L-1)(mu-OA(c))(4)](n) (5) and the 2-D coordination polymer {[Cu(L-3)(2)(H2O)(2)](L-1)(H2O)(2)(PF6)(2)}(n) (6) were organized by a similar procedure, with the main difference of the secondary ligand L 3 being used only in the synthesis of 6. The structural diversity of the six coordination polymers perhaps mainly results from the changes of secondary ligands and bridging anions, showing that the two factors play important roles in the construction of various metal-organic frameworks.