Red phosphorescent cuprous halide/pseudohalide coordination polymers with pyrimidine-2-thionates as Co-ligands

Abstract

Hydro(solvo)thermal treatment of Cu(II) and pyrimidine-2-thione (pymtH) in the presence of halide/pseudohalide has generated four phosphorescent cuprous pyrimidine-2-thiolate complexes, namely Cu₂(pymt)Cl (1) and Cu₃(pymt)₂(SCN) (2), Cu₃(pymt)₂I (3) and Cu₁₁(pymt)₄I₇ (4). Complex 1 has a layered structure constructed by a [Cu₂SCl]_∞ staircase chain; 2 contains helical chains [Cu₃(pymt)₂]_nⁿ⁺ that are further linked by μ₃-1,2κS:3κN SCN into a 2-D layer, in which two adjacent helical chains are heterochiral; 3 is structurally related to 2 because it also contains a helical chain [Cu₃(pymt)₂]_nⁿ⁺. Differently the helical chain in 3 is attached by iodides to form a neutral two-fold screw chain; 4 consists of linear, trigonal and tetrahedral copper(I) sites, some of which are half occupied and has a complicated layered structure. Two unprecedented coordination modes of μ₄-1κS:2,3κS:4κN′ and μ₅-1,κN:2,3,4,κS:5,κN′ of pymt are observed. The presence of helical [Cu₃(pymt)₂]_nⁿ⁺ chains in both 2 and 3 leads us to guess that the [Cu₃(pymt)₂]_nⁿ⁺ chain is possibly an elementary structural species in solution. In the solid state and at ambient temperature, 1–4 all show interesting phosphorescent emissions: a strong red emission and a weak higher energy blue emission band. The weak higher energy blue emissions are tentatively assigned as originating from the halides/pseudohalides to aromatic pyrimidine π* charge transfer while the low-energy red emissions are tentatively assigned as from ligand-to-metal charge transfer (LMCT) and/or metal-to-ligand charge-transfer (MLCT) characters, mixed with metal-centered (ds/dp) states modified by Cu–Cu interactions.