Syntheses and Structures of Three Unprecedented Metal−Ciprofloxacin Complexes with Helical Character

Self-assemblies of the fluoroquinolone ciprofloxacin (cfH) and zinc salt in the presence of V-shaped polycarboxylate
ligands yielded three unprecedented helical metal−cfH complexes, namely, [Zn(cfH)(Hbtc)]·H2O (1), [Zn2(cfH)2(odpa)] (2), and
[Zn2(cfH)2(bptc)]·4H2O (3) (btc = 1,3,5-benzenetricarboxylate, odpa = 4,4‘-oxydiphthalate, bptc = 3,3‘,4,4‘-benzophenonetetracarboxylate). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental
analyses, IR spectra, and thermogravimetric analyses. Compound 1 is a unique helical metal−cfH complex containing three types
of helices. This case is still rare in metal−organic complexes. Compound 2 exhibits a novel two-dimensional (2D) chiral layer
structure featuring two distinct helices, in which the hydrogen-bonded double-stranded helix is quite uncommon. The chiral layer
structure of 3 is similar to that of 2. However, due to the existence of guest water molecules, the pitch of the helices in 3 is longer
than those in 2, which indicates that the pitch of the helices in 2 and 3 could be tuned through the incorporation of guest molecules.
To the best of our knowledge, compounds 1−3 represent the first examples of metal−quinolone complexes containing helical and
chiral structures. Furthermore, the photoluminescent properties of compounds 1 and 3 were studied.