Luminescent, magnetic and ferroelectric properties of noncentrosymmetric chain-like complexes composed of nine-coordinate lanthanide ions

Abstract

Reaction of the chiral ligand (−)-4,5-pinenepyridyl-2-pyrazine (L) with Ln(hfac)₃·2H₂O precursors [hfac⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate, Ln = Sm³⁺ (1), Eu³⁺ (2), Tb³⁺ (3) and Dy³⁺ (4)] in methanol solution led to the formation of four noncentrosymmetric lanthanide complexes with the general formula [Ln(hfac)₃L]_n·H₂O. The single-crystal X-ray diffraction analyses revealed that they are isostructural and take a one-dimensional (1D) chain structure based on the Ln(hfac)₃L repeating units, in which the nine-coordinate Ln³⁺ ions reside in a tricapped trigonal prism (TTP) environment never reported in previous 1D chain lanthanide complexes. The investigations of their photophysical properties showed that complexes 1, 2 and 3 exhibit characteristic emissions of Sm³⁺, Eu³⁺ and Tb³⁺ ions with respective luminescent lifetime values of 0.065, 1.066 and 0.129 ms, while complex 4 does not display any emission. The different luminescent intensities and lifetimes among them were further discussed in detail. Moreover, the magnetic properties of complexes 1–4 were assessed with a special emphasis on the Dy³⁺ complex 4. Alternating-current (ac) magnetic susceptibility measurements indicated that field-induced two-step slow magnetic relaxation processes were observed in 4, indicating the single-molecule magnet (SMM) behavior of 4. In addition, the noncentrosymmetric complexes 1–4 crystallizing in the same polar point group (C_s) exhibit both ferroelectric and nonlinear optical properties at room temperature. All these features make them multifunctional crystalline molecule materials.