Multifunctional Lanthanide Molecular Ferroelectrics [ R / S -H ₂ MPPA][Ln(btfa) ₄ ] ₂ Constructed by Hydrogen Bond Linking Functional Blocks

Chiral molecular ferroelectrics with optical and magnetic functions have attracted widespread attention, but their rational construction is extremely challenging due to the strict requirements of crystal symmetry. Herein, based on the construction strategy of hydrogen bond linking functional blocks, two pairs of enantiomeric multifunctional lanthanide molecular ferroelectrics [R/S-H2MPPA][Ln(btfa)4]2 (Tb-R (1), Tb-S (2), Dy-R (3), and Dy-S (4)) were obtained by using anionic functional blocks [Ln(btfa)4]− (Ln = TbIII and DyIII, Hbtfa = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) and chiral protonated amines cation [R/S-H2MPPA]2+ (R/S-MPPA = (R/S)-2-methylpiperazine). Ferroelectric characterization and second-harmonic generation (SHG) measurements confirmed that Tb-R (1) and Dy-R (3) exhibit both ferroelectricity and second-order nonlinear optical (NLO) activity. At room temperature, the spontaneous polarizations (Ps) of Tb-R (1) and Dy-R (3) are 1.02 μC·cm–2 and 1.01 μC·cm–2, respectively. Differential scanning calorimetry (DSC) revealed that the P21 ferroelectric phase of Tb-R (1) and Dy-R (3) remained stable up to 414.9 and 421.6 K. Furthermore, Tb-R (1) exhibits obvious characteristic yellow-green luminescence of TbIII ions. Dy-R (3) shows field-induced single-ion magnet (SIM) behavior. This study demonstrates that integrating chiral protonated amines with [Ln(btfa)4]− functional blocks can be an effective strategy for precisely constructing molecular ferroelectrics coupled to magnetic or photoluminescent properties.