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 π−π interactions. In drastic contrast, 3 and 4 exhibit a three‐dimensional structure consisting of one‐dimensional polymeric chains held together through π−π 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 } n 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)