Magnetic Ordering-Induced Multiferroic Behavior in [CH₃NH₃][Co(HCOO)₃] Metal–Organic Framework

We present the first example of magnetic ordering-induced multiferroic behavior in a metal–organic framework magnet. This compound is [CH₃NH₃]­[Co­(HCOO)₃] with a perovskite-like structure. The A-site [CH₃NH₃]⁺ cation strongly distorts the framework, allowing anisotropic magnetic and electric behavior and coupling between them to occur. This material is a spin canted antiferromagnet below 15.9 K with a weak ferromagnetic component attributable to Dzyaloshinskii–Moriya (DM) interactions and experiences a discontinuous hysteretic magnetic-field-induced switching along [010] and a more continuous hysteresis along [101]. Coupling between the magnetic and electric order is resolved when the field is applied along this [101]: a spin rearrangement occurs at a critical magnetic field in the ac plane that induces a change in the electric polarization along [101] and [10-1]. The electric polarization exhibits an unusual memory effect, as it remembers the direction of the previous two magnetic-field pulses applied. The data are consistent with an inverse-DM mechanism for multiferroic behavior

[(CH₃)₂NH₂]₇Pb₄X₁₅ (X = Cl^– and Br^–), 2D-Perovskite Related Hybrids with Dielectric Transitions and Broadband Photoluminiscent Emission

We have prepared two new lead halides with the novel general formula of DMA₇Pb₄X₁₅ (DMA = [(CH₃)₂NH₂]⁺ and X = Cl^– or Br^–) by using an easy route under mild conditions at room temperature. These compounds exhibit an unprecedented crystal structure, are formed by layers of distorted [PbX₆] octahedra, which share corners and faces, and contain intercalated DMA cations. Very interestingly, they display dielectric transitions, which are related to a partial order–disorder process of the DMA cations between 160 and 260 K. Additionally, these new layered hybrids exhibit a broadband photoluminiscent emission, which is related to the structural distortions of the [PbX₆] octahedra. These findings not only open up large possibilities for future optoelectronic applications of these materials, but they also offer a novel playground for an easy modulation of electrical and optical properties of hybrid organic–inorganic materials. We anticipate that this novel A₇Pb₄X₁₅ formula can be adequate to tune the family of the hybrid lead halides using other alkylammonium cations, such as methylammonium, formamidinium, or ethylammonium, to improve their photoelectronic properties