Influence of synthesis condition on product formation: hydrothermal auto-oxidated synthesis of five copper halides with ratio of Cu(I)/Cu(II) in 1:1, 2:1, 3:1, 4:1 and 1:0

The hydrothermal synthesis and structural characterization of five copper iodides derived from chelated ligands, 1, 10-phenanthroline (phen), ethylenediamine (en) and 1, 3-propanediamine, are reported. Except monovalent copper compound 1 ((phen)Cu3I3 1), other four compounds ([Cu(phen)2I][CuI2] 2, [Cu(phen)2I][Cu3I4] 3, [Cu(en)2][Cu4(phen)2I6] 4 and [Cu(1, 3-propanediamine)2][CuI2]2 5) are mixed-valent Cu(I)–Cu(II) compounds by partially auto-oxidated from Cu(I). Supramolecular frameworks of these compounds can be assembled by C/N–H⋯I hydrogen bonds, Cu(I)–Cu(I) interaction, weak Cu–I semicoordinate interaction, C–H⋯π and π–π stacking interactions. Itʹs noteworthy that we find hydrothermal synthesis under higher pH value, higher synthesis temperature and longer reaction time can obtain higher ratio of Cu(I)/Cu(II) copper iodides and organic ligand with lower steric hinderance is prone to coordinated with divalent copper to form cation unit. Finally, the fluorescent study shows 1 exhibits intense orange–red luminescence with long lifetime at 293 K and more intense emission and longer lifetime at 77 K. Moreover, the room temperature EPR spectra of above five compounds not only show the valence of copper but demonstrate the coordination environment of Cu(II) centre.