Three novel cadmium(II) complexes from different conformational 1,1′-biphenyl-3,3′-dicarboxylate

Three novel cadmium(II) coordination polymers, [Cd-2(4,4'-bipy)(3,3'-bpda)(2)](n) (1), [Cd-4(bpe)(3)(mu-H2O)(2)(3,3'-bpda)(4)](n) (2), and [Cd-2(3,3'-bpda)(2)](n) (3), have been hydrothermally synthesized by 1,1'-biphenyl-3,3'-dicarboxylate (3,3'-bpda) and Cd(NO3)(2).4H2O with exo-bidentate pyridyl-containing ligands, 4,4'-bipyridine (4,4'-bipy), 1,2-bi(4-pyridyl)ethane (bpe), and 1,3-di(4-pyridyl)propane (dpp), respectively. X-ray crystal structural analyses reveal that the three polymers possess different novel structural motifs derived from different conformations of the 3,3'-bpda ligand. In 1, 3,3'-bpda in a trans conformation links paddle wheel dimeric cadmium-tetracarboxylate building units resulting in a two-dimensional layer, which is further bridged by 4,4'-bipy generating a three-dimensional framework with a 3-fold interpenetrating structure. 3,3'-bpda in 2 has a cis conformation and bridges among six-coordinated and seven-coordinated Cd-II centers forming a tetranuclear cadmium unit, which is further connected by bpe producing a two-dimensional layer. The larger cavities in a layer of 2 result in mutually perpendicular interpenetrating two-dimensional layers. Complex 3 is an unprecedented three-dimensional polymer consisting of double chains formed from two different trans bridging 3,3'-bpda and five-coordinated cadmium(II) centers.