Self-assembly of [Cu3I2]- or [CuI]n-based (n = 2, 4, and ∞) coordination polymers from unsymmetrical bis(pyridyl) and in situ ligands: syntheses, structures, and properties

Abstract

Five new copper coordination polymers, [CuI(L1a)]_n (1), [Cu_1.5I(dmtrz)_0.5(PPh₃)]_n·0.5n(CH₃CN) (2), [Cu₂I₂(L1b)]_n (3), [Cu₄I₄(L2)]_n·nH₂O (4), and [CuI(L3)]_n (5) (L1a = N-(pyridin-2-ylmethyl)-N-(pyridin-3-yl)formamide, Hdmtrz = 3,5-dimethyl-4H-1,2,4-triazole, L1b = N-(pyridin-2-ylmethylene)pyridin-3-amine, L2 = N-(pyridin-4-ylmethyl)pyridin-3-amine, L3 = N-(pyridin-3-ylmethyl)pyridin-2-amine), have been synthesized by the solvothermal reactions of CuI and three unsymmetrical bis(pyridyl) ligands in mixed methanol–acetonitrile solution and characterized using elemental analysis, IR, TG, PL, XPS, powder and single-crystal X-ray diffraction. In 1, the ligand L1a is in situ generated from N-(pyridin-2-ylmethyl)pyridin-3-amine (L1) and bridges adjacent Cu₂I₂ rhomboid units, forming a double chain structure. The rare Cu₃I₂ clusters in 2 are linked by the dmtrz⁻ monoanion to generate a linear chain structure, in which the dmtrz⁻ monoanion is in situ synthesized by a non-ammonia pathway. The L1b in 3 is also in situ generated from L1 and connects adjacent chair like Cu₄I₄ clusters into a (4,4) layer structure. By contrast, the Cu₄I₄ cubanes in 4 are linked by the L2 ligands to form a 2-fold interpenetration (4⁴·6²) net. The Cu(I) cations in 5 are linked by the μ₃-I⁻ ions into infinite double-stranded [Cu₂I₂]_n ladder chains, which are further extended into a layer structure by the L3 molecules. Moreover, the binding energies of the Cu 2p_3/2 level in the XPS spectra are typical for a Cu(I) oxidation state. For the N1s, the different binding energies in the XPS spectra can be attributed to the N atoms with different chemical environments. Luminescent property investigation shows that only 5 exhibits a blue emission maximum at 475 nm.