A New Type of Single-Helix Coordination Polymer with Mixed Ligands [M₂(phen)₂(<i>e,a</i>-<i>cis</i>-1,4-chdc)₂(H₂O)₂]<i>_n</i> (M = Co and Ni; phen = 1,10-phenanthroline; chdc = cyclohexanedicarboxylate)

A new family of single-stranded helices coordination polymers with mixed ligands, [M2(phen)2(e,a-cis-1,4-chdc)2(H2O)2]n (1, M = Co; 2, M = Ni; chdc = cyclohexanedicarboxylic acid; phen = 1,10-phenanthroline), were prepared
under hydrothermal conditions and characterized by elemental analyses, IR spectra, TG analysis, and single-crystal X-ray diffraction analysis. X-ray crystal structural analyses reveal that 1 and 2 are isomorphic and belong
to the monoclinic system. C40H36Co2N4O10, P21/c, a = 10.0566(5) Å, b = 8.8843(5) Å, c = 20.2912(14) Å, β =
100.052(3)°, Z = 2 for 1; and C40H36Ni2N4O10, P21/c, a = 9.8921(6) Å, b = 9.0151(4) Å, c = 20.1628(17) Å, β
= 100.31(2)°, Z = 2 for 2. In the structures of 1 and 2, the 1,4-chdc ligand possesses only one kind of e,a-cis-conformation although there are both cis- and trans-conformations in the raw material. Two oxygen atoms of one
carboxyl in 1,4-chdc ligand and another oxygen atom of contraposition carboxyl link adjacent Co or Ni atoms into
an infinite 1-D zigzag chain. The most attractive structural feature of 1 and 2 is that they both exhibit an infinite
chiral chainlike structure with 21 helices along the b axis. In addition, the right-handed and the left-handed chains
are alternate. Meanwhile, the adjacent chains of 1 and 2 are linked via hydrogen bonds into 2-D network structures,
which further form 3-D frameworks via π-π interactions of 1,10-phen.