pH Influence on the Structural Variations of 4,4′-Oxydiphthalate Coordination Polymers

Five new Zn­(II)/ODPT/bpe compounds, namely, {[Zn­(bpe)­(H2O)2]­(H2ODPT)·3H2O}n (1), {[Zn4(ODPT)2(bpe)3(H2O)2]2(bpe)·7H2O}n (2), {[Zn2(ODPT)­(bpe)2]2·7H2O}n (3), {Zn4(ODPT)2(bpe)}n (4), and
{Zn2(ODPT)­(bpe)­(H2O)2}n (5) (ODPT = 4,4′-oxidiphthalate,
bpe =1,2-bis­(4-pyridyl)­ethane), have been synthesized through a hydrothermal
method under different pH conditions, and characterized by single-crystal
X-ray diffraction, element analysis, infrared spectra (IR), and thermogravimetric
(TG) analyses. Compound 1 shows a 3D network framework
constructed by the 1D linear [Zn­(bpe)­(H2O)4]n2+ cationic chains through extensive
hydrogen-bonding. Compound 2 displays an unusual three-dimensional
(3D) meso-racemic self-penetrating coordination network with distinct
chiral information in the interpenetrating networks. Compound 3 features a novel 4-connected (4·62·83)­(42·62·82) topology,
also exhibiting an intriguing 3D self-penetrating structure formed
by triple- and double-stranded helical chain motifs. Compounds 4 and 5 are based upon 3D pillared-layer frameworks
constructed from Zn2+ and ODPT4‑, and further
consolidated by the bpe ligands as molecular pillars. The most striking
feature of 5 is that achiral ODPT4– ligands link the Zn cations into right-handed 21 helical
chains, and the chiral information is transferred to the 3D framework
with a chiral space group C2221. The diversity
of the product structures illustrates the marked sensitivity of the
coordination chemistry of the V-shaped multicarboxylate ligand (H4ODPT) to the pH value of the solution. Moreover, the thermal
dynamic properties and fluorescent properties of all compounds are
also investigated.