A Series of Coordination Polymers Exhibiting Dual Chiral Features and Diverse Interhelical Interactions

With
the aim of integrating the inherent chirality of ligand and
the chirality induced by conformational twists of the asymmetric skeleton
of the ligand upon its coordination, (1R,3S)-1,2,2-trimethyl-3-{[5-(2-hydroxy)­phenyl-1,3,4-oxadiazol-2-yl]}­cyclopentanecarboxylic
acid (H2L) was prepared from the acylation reaction of
chiral camphoric acid with salicylhydrazide. The reactions of H2L with transition metal ions gave five coordination polymers
{[Co­(L)­(py)2]·DMF}n (1), {[Ni­(L)­(py)2]·DMF}n (2), [Cu­(L)­(py)]n (3), [Zn2(L)2(py)2]n (4), and [Cd2(L)2(py)2]n (5). Complexes 1 and 2 show only
right-handed helical chains with homochiral helical discrimination
by interhelical nonclassic hydrogen bonds C–H···O.
However, 3–5 contain right-handed
and left-handed helical chains simultaneously, which are arranged
alternately and interact with each other by π···π
interactions for 3 and by interchain M–O–M
linkage for 4 and 5, respectively. The chiralities
of these compounds derive from the inherent chirality of the ligand,
as well as from the conformational twists of the asymmetric ligand
skeleton. The results also reveal the role of different metal ions
in the construction of chiral coordination polymers. The fluorescent
studies revealed emission bands assigned to intraligand transmission
for complexes 1–5.