Molecular-based materials with such functions as catalysis, magnetism and coordinate clathrations of one-, two-, and three-dimensional infinite frameworks have been extensively studied. Although rigid bridged ligands were frequently employed to construct these materials, flexible ligands were exploited less for this purpose. A one-dimensional polymer ${[Cd_2(=mu-bpe)_2](mu-bpe)}(NO_3)_4}_n$ is prepared ; its structure is strikingly characterized by heptacoordinate Cd ions as well as by a unique main framework.