Crystal-engineering and luminescence studies of 1,3,5-tris(3-pyridylethynyl)benzene or 1,3,5-tris(4-pyridylethynyl)benzene with copper(i) iodides

Abstract

Two isomeric C₃-symmetric ligands, 1,3,5-tris(3-pyridylethynyl)benzene (L1) and 1,3,5-tris(4-pyridylethynyl)benzene (L2), were used to react with CuI to give a series of coordination frameworks containing various CuI clusters, {[(Cu₂I₂)₂(L1)₂]·C₆H₅CH₃}_n (1), {[(Cu₂I₂)_1.5(L1)₂]·1.5C₆H₆·CH₃CN}_n (2), [(Cu₂I₂)_0.5(L1)]_n (3), {[(Cu₂I₂)_0.5(L2)]·C₆H₆}_n (4), and {[(Cu₂I₂)(L2)]·C₆H₆}_n (5), which have been isolated and structurally characterized by X-ray diffraction studies. Although 1 is simultaneously composed of a rhombohedral Cu₂I₂ cluster and a step-cubane Cu₄I₄ cluster and 2 contains two types of rhombohedral Cu₂I₂ clusters in the frameworks, both give similar 3-D supramolecular architectures interpenetrated by 2-D layer frameworks. 3 forms a 1-D double-zigzag framework, and significantly the interlocking of the 1-D frameworks into the 28-membered rings of the adjacent chains generates a novel 1-D (1-D → 1-D) polyrotaxane framework. However, as the structural and isomeric analogue, 4 only forms a 1-D double-zigzag framework leading to a 2-D supramolecular structure by π⋯π interactions and C–H⋯N hydrogen bonding. 5, composed of polymeric (Cu₂I₂)_n cluster chains, forms a 3-D coordination framework and interpenetrates to give a 2-fold interpenetrated framework. It is noted that these coordination frameworks show various structural motifs depending on the reaction conditions and ligands’ backbones. In addition, the low-energy emissions at 538–615 nm for 1–5 either at room temperature or at 77 K have been observed, which are most likely to originate from an iodo-to-copper charge-transfer transition, possibly modified by Cu(I)⋯Cu(I) interactions.