Twisting MOFs into Ferroelectrics

MATERIALS SCIENCE Ferroelectric materials, in which the bulk lattice exhibits a spontaneous net dipole moment, have numerous applications as memory elements, insulators, and resonators. Typical ferroelectrics are composed of inorganic salts such as BaTiO3 and LiNbO3, but there is interest in finding organic or organometallic alternatives. Ye et al. explored the potential for ferroelectricity in a metal-organic framework (MOF) architecture, a porous motif that has been studied for chemical applications such as sorption or catalysis. They found that hydrothermal reaction of CdCl2 and NaN3 with homochiral N -(4-cyanobenzyl)-( S )-proline yields a MOF with the necessary noncentrosymmetric lattice symmetry; x-ray crystallography revealed a slight displacement of the Cd atoms in their octahedral sites. The temperature dependence of the dielectric loss suggests that the Cd-Cl bond vibration or the displacement of the proton on a tetrazoyl group (the adduct of azide-to-nitrile cycloaddition) underlies the relaxation process, and the authors estimate a dielectric constant of ∼40 for this material at ∼220 K. — PDS J. Am. Chem. Soc. 128 , 10.1021/ja060856p (2006).