Reactant ratio-modulated six new copper(i)–iodide coordination complexes based on diverse [CumIm] aggregates and biimidazole linkers: syntheses, structures and temperature-dependent luminescence properties

Abstract

A total of six copper(I)–iodide coordination complexes with diverse [Cu_mI_m] aggregates and bidentate biimidazole bridging ligands, [Cu₂I₂(dmimb)]_n (1), [Cu₄I₄(dmimb)]_n (2), [Cu₆I₆(dmimb)₃]_n (3), [Cu₄I₄(dimb)]_n (4), [Cu₂I₂(dimb)₂]_n (5), and [Cu₄I₄(dimb)₃]_n (6), (dmimb = 1,4-di(2-methyl-imidazol-1-yl)butane, dimb = 1,3-di(imidazol-1-yl)benzene), have been synthesized and structurally characterized by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Single-crystal X-ray diffraction analysis reveals that 1 is a double-chain based 1D ribbon incorporating a discrete [Cu₄I₄] stepped cubane aggregate. Complex 2 is a 2D layer based on the 1D infinite [Cu₆I₆]_n column aggregate. Complex 3 is a triple-chain based 1D ribbon incorporating a discrete ladder-like [Cu₆I₆] aggregate. Interestingly, 1 and 3 are a pair of genuine supramolecular isomers controlled by the reaction ratio with an identical chemical composition. In the 2D layered structure of complex 4, the rare “S-shaped-double-bowl” Cu₁₀I₁₀ aggregate is observed and share the Cu₂I₂ rhomboids to form the 1D infinite [Cu₁₀I₁₀]_n column. Complex 5 is a binuclear 18-membered metal–organic macrocycle with [CuI] monomeric units. Complex 6 is also a 2D layer constructed from a 1D infinite [Cu₈I₈]_n aggregate which consists of a 1D infinite [Cu₆I₆]_n column and a [Cu₂I₂]_n ladder. In the overall view, the biimidazole linkers play an important role in the formation of diverse [Cu_mI_m] aggregates as well as the resulting structures and topologies. The structural changes of 1/2/3 and 4/5/6 are highly influenced due to the change of the reaction stoichiometry. For 1, 2, 5 and 6, they are non-emissive at both 298 K and 77 K, whereas 3 and 4 exhibit interesting temperature-dependent luminescence properties. The correlation between the luminescence thermochromism and the temperature-dependent variation of the Cu⋯Cu distance is also elucidated.