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

Reaction of the chiral ligand (-)-4,5-pinenepyridyl-2-pyrazine (L) with Ln(hfac)(3)center dot 2H(2)O 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)(3)L](n)center dot 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 Ln(3+) 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.