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 ODPT^4‑, and further consolidated by the bpe ligands as molecular pillars. The most striking feature of 5 is that achiral ODPT^4– 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.