Ferroelectric Order in the Chiral Coordination Polymers [Ln₂(L*)₂(ox)₂(H₂O)₂] with Ln=Gd³⁺ or Dy³⁺, L*=((S, S)‐1,3‐bis(1‐Carboxylethyl)imidazolium and Ox=Oxalate.

We evidence the ferroelectricity of two isostructural magnetic coordination networks obtained from a chiral imidazolium dicarboxylate salt ((S, S)‐1,3‐bis(1‐carboxylethyl)imidazolium or [HL*]) and Gd 3+ or Dy 3+ ions in presence of oxalic acid (H 2 ox). The two compounds exhibit a chiral structure P 1 and ferroelectric properties. The crystallographic study shows that the Dy based‐compound is isostructural to the Gd analog. The non‐centrosymmetry of the two samples was further checked by means of nonlinear optical spectroscopy. The room temperature ferroelectric character of the compounds has been investigated through by an original method, derived from that used for thin films, made possible by preparing the sample as thin slices of resin containing inclusions of the coordination compounds.