Three Novel Cadmium(II) Complexes from Different Conformational 1,1‘-Biphenyl-3,3‘-dicarboxylate

Three novel cadmium(II) coordination polymers, [Cd2(4,4‘-bipy)(3,3‘-bpda)2]n (1), [Cd4(bpe)3(μ-H2O)2(3,3‘-bpda)4]n (2), and [Cd2(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 CdII 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.