Postsynthetic Approach for the Rational Design of Chiral Ferroelectric Metal–Organic Frameworks

Ferroelectrics (FEs) are materials of paramount importance with a wide diversity of applications. Herein, we propose a postsynthetic methodology for the smart implementation of ferroelectricity in chiral metal-organic frameworks (MOFs): following a single-crystal to single-crystal cation metathesis, the Ca²⁺ counterions of a preformed chiral MOF of formula Ca₆^II{Cu^II₂₄[(S,S)-hismox]₁₂(OH₂)₃}·212H₂O (1), where hismox is a chiral ligand derived from the natural amino acid l-histidine, are replaced by CH₃NH₃⁺. The resulting compound, (CH₃NH₃)₁₂{Cu^II₂₄[(S,S)-hismox]₁₂(OH₂)₃}·178H₂O (2), retains the polar space group of 1 and is ferroelectric below 260 K. These results open a new synthetic avenue to enlarge the limited number of FE MOFs.