Syntheses and characterizations of metal-organic frameworks with unusual topologies derived from flexible dipyridyl ligands

Two flexible exo-bidentate ligands, 2,2'-bis(3-pyridylmethyleneoxy)-1,1'-biphenylene (3,3'-bpp) and 2,2'-bis(4-pyridylmethyleneoxy)-1,1'-biphenylene (4,4'-bpp), were synthesized and employed for the preparation of coordination polymers. Seven metal-organic complexes, [Zn-2(3,3'-bpp)(2)Cl-4] (1), [Zn-2(3,3'-bpp)(2)Br-4] (2), [Zn(4,4'-bpp)Cl-2](n) (3), [Zn(4,4'bpp)Br-2](n) (4). [Co(4,4'-bpp)(2)(SCN)(2)](n) (5), {[Cd(4,4'bpp)(2)(SCN)(2)].2H(2)O}(n) (6) and [Cd(4,4'-bpp)(dca)(2)](n) (7) (dca(-) = dicyanamide), have been obtained through self-assembly reactions of 3,3'-bpp or 4,4'-bpp with the divalent metal ions Zn-II, Co-II and Cd-II. Crystal structure analyses reveal that 1 and 2 are dinuclear metallomacrocycles, are isomorphous and possess a layer network built from metallomacrocycles through pi-pi interactions. In drastic contrast, 3 and 4 exhibit a three-dimensional structure consisting of one-dimensional polymeric chains held together through pi-pi interactions between adjacent pyridyl rings. The metal-organic frameworks of 5, 6, and 7 possess unusual topologies: Complex 5 is a two-dimensional polymer based on folded rectangular boxes and zigzag chains, whereas 6 is a polycatenated species consisting of inclined interpenetrating two-dimensional layers, and each layer is constructed by the alternating assembly of left-hand (M) and right-hand (P) cylindrical 2(1) helices. In 7, dca(-) connects Cd-II centers forming a two-dimensional {Cd(dca)(2)}, layer, which is fused with (M)- and (P)-Cd-(4,4'-bpp) helical chains into a three-dimensional structure. The results suggest that the nature of organic ligands and the coordination preferences of transitional metal ions have a great influence on the structures of metal-organic complexes. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).