Homochiral Multiferroic Cyanido-Bridged Dimetallic Complexes Assembled by C−F⋅⋅⋅K Interactions

Abstract

Cyanido-bridged dimetallic complexes are attracting attention due to their varied structures and properties. However, homochiral cyanido-bridged dimetallic complexes are rare, and making them ferroelectric is a great challenge. Introducing C−F⋅⋅⋅K interactions between the guest chiral cations and the host [KFe(CN)6]2− framework, gives three-dimensional cyanido-bridged dimetallic multiferroics, [R- and S-3-fluoropyrrolidinium]2[KFe(CN)6] (R- and S-3-FPC). The mirror-symmetric vibrational circular dichroism (VCD) signal shows their enantiomeric nature. R- and S-3-FPC crystallize in the same chiral-polar space group P21 at 298 K. Piezoresponse force microscopy (PFM), polarizing optical microscopy, and temperature-dependent second-harmonic generation (SHG) measurements show their multiferroic properties (the coexistence of ferroelectricity and ferroelasticity), in line with the Aizu notation of 222F2. R-3-FPC shows excellent ferroelectricity with saturated polarization up to 9.4 μC cm−2.