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.