Highly photo- and triboluminescent lanthanide(iii) coordination polymers based on diphosphine dioxides containing azaheterocyclic linkers

Abstract

The reactions of Eu(III) and Tb(III) hexafluoroacetylacetonates (hfac⁻) with 2,4-bis(diphenylphosphino)pyrimidine dioxide (L¹), 4,6-bis(diphenylphosphino)pyrimidine dioxide (L²), or 3,6-bis(diphenylphosphino)pyridazine dioxide (L³) afforded a new series of one-dimensional coordination polymers [LnL(hfac)₃]_n (L = L¹, L², and L³). Compounds [TbL²(hfac)₃]_n and [LnL³(hfac)₃]_n (Ln = Eu, Tb) consist of the eight-coordinated Ln(III) atoms linked by L² and L³ ligands in the O,O′-bridging manner (an O₈ polyhedron). In [LnL¹(hfac)₃]_n (Ln = Eu, Tb) and [EuL²(hfac)₃]_n, one of the N atoms of bridging diphosphine dioxide is involved in the coordination to the Ln³⁺ ion resulting in a N₁O₈ polyhedron. All coordination polymers exhibit high thermal stability above 300 °C. The Eu(III) coordination polymers display strong photoluminescence with the solid-state quantum yield up to 61% observed for [EuL¹(hfac)₃]_n. The chelating coordination of L¹ and L² increases considerably the energy transfer efficiency from the ligands to Eu(III) compared to that of L³. The centrosymmetric coordination polymers [LnL¹(hfac)₃]_n exhibit strong triboluminescence that is clearly observed even in daylight at ambient temperature, while their non-centrosymmetric analogue [EuL²(hfac)₃]_n displays lower triboluminescent activity, which is visible only in the dark.