Three cuprous coordination polymers based on bisbenzoxazole: Syntheses, structures, luminescence and electrochemical properties

Abstract

Three cuprous coordination polymers, namely: {[Cu(BBO)3]·PF6}n (1), {[Cu(BBO)2(CH3CN)2]·BF4}n (2) and {[Cu(BBO)2(SPPh3)]·BF4}n (3), bearing a bisbenzoxazole ligand, 2,2′-(1,4-butanediyl)bis-1,3-benzoxazole (BBO), have been synthesized, and structurally characterized by elemental analyses, IR, UV–Vis and single-crystal X-ray diffraction. The structural analysis revealed that the structures of coordination polymers 1 and 3 are both three-coordinated and show distorted trigonal planar geometry, but 2 is four-coordinated and a slightly distorted tetrahedron environment. In coordination polymer 1, adjacent copper(I) ions were bridged by three independent BBO to form a two-dimensional planar layer framework in which PF6− anion is filled in the hole. Two BBO link Cu(I) ions into a one-dimensional zigzag chain in coordination polymer 2, while acetonitrile as an ancillary ligand distributed on both sides of the one-dimensional chain. Coordination polymer 3 exhibits a single-stranded helix chain structure by two BBO bridging adjacent copper(I) ions. Luminescence properties investigation show that 1 have two emission peaks, which attributed to π–π* and n–π* transitions. However 2 and 3 only had one emission peak, which may be attributed to [MLCT(d10(Cu) → π*]. This may be due to the synergy of the auxiliary ligands in coordination polymers 2 and 3. The cyclic voltammogram of 1–3 represent quasi-reversible Cu2+/Cu+ pairs.