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

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 P2 ₁ 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 .
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