Protonated N-oxide-4,4′-bipyridine: from luminescent BiIII complexes to hybrids based on H-bonded dimers or H-bonded open 2D square supramolecular networks

Abstract

The N-oxide-4,4′-bipyridine (bp4mo) ligand has been rarely used in coordination or supramolecular chemistry. Depending on experimental conditions in the bp4mo/BiX₃ (X = Cl, Br) system, several compounds, in which the degree of protonation of bp4mo (τ = H/bp4mo) varies, have been stabilized. In acidic conditions, either a complete N-protonation and a partial O-protonation (τ = 1.5) or a complete N-protonation (τ = 1.0) can occur, leading to either a hybrid salt based on H-bonded dimers [H(Hbp4mo)₂]³⁺, or to O(Hbp4mo)–Bi photoluminescent complexes. In neutral conditions, a partial N-protonation (τ = 0.5) occurs in [H(bp4mo)₂][BiCl₄]. Although the N-oxide parts are free to bind Bi³⁺ cations, the organic entities prefer self-organizing through H-bonding (NH⋯N and CH⋯O) to give an impressive 2D supramolecular square network which accommodates the 1D BiCl₄⁻ polymeric anion.