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 (μ-H 2 O) 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(NO 3 ) 2 ·4H 2 O 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.