Synthesis and photoluminescence properties of different structural cuprous complexes regulated by benzoxazole ligands and halogen/pseudohalide ions

Abstract

Reaction of 2-(2′-pyridyl)benzoxazole (2-PBO), 2-(4′-pyridyl)benzoxazole (4-PBO) and 2,2-(1,4-butanediyl)bis-1,3-benzoxazole (BBO) ligands with CuX (X = I, Br, SCN) afforded a binuclear copper(I) complex [Cu(2-PBO)(μ2-I)]2 (1) and three copper(I) coordination polymers [Cu4(4-PBO)4(μ3-I)4]n (2), {[Cu(4-PBO)(μ3-SCN)]2}n (3) and {[Cu(BBO)(μ2-Br)]2}n (4). The structural analysis revealed that the all copper(I) ions are four-coordinated and the geometric structure around the central copper(I) atom possessing slightly distorted tetrahedral geometry in complexes 1–4. Halogen or pseudohalide ions can not only act as counter anions, but also as ligands participation in coordination when the cuprous ion coordination sites are not saturated. Due to the different coordination modes of the benzoxazole ligands, in order to satisfy the tetra-coordination of cuprous ions, halogen or pseudohalide ions adopt μ2 and/or μ3-bridging modes to synergistically complete coordination. Photoluminescence investigation show that complexes 1, 3 and 4 have two emission peaks, the high energy band peak is attributed to MLCT[d10(Cu)→π*] and XMCT, the low energy band peak is caused by the 3CC emission. This may be due to the presence of μ2-X (X = I, Br, S) in these complexes. However complex 2 only had one emission peak, which may be attributed to MLCT[d10(Cu)→π*] and XMCT.