Enhancing the chemical flexibility of hybrid perovskites by introducing divalent ligands

Negative linear compressibility exhibited by the hybrid perovskite [(NH2)3C]Er(HCO2)2(C2O4)

Extended framework materials with specific topologies can exhibit unusual mechanical behaviour, such as expanding in one direction under hydrostatic (uniform) pressure, known as negative linear compressibility (NLC). Here, two hybrid perovskite frameworks with winerack structures, a known NLC topology, are investigated under pressure. [C(NH2)3]Er(HCO2)2(C2O4) exhibits NLC from ambient pressure to 2.63(10) GPa and is the first reported NLC hybrid perovskite from ambient pressure. However, isostructural [(CH3)2NH2]Er(HCO2)2(C2O4) instead compresses relatively moderately along all axes before it undergoes a phase transition above 0.37(10) GPa. The differences in the mechanical properties can be interpreted from differences in host-guest interactions within these frameworks, primarily their hydrogen bond networks.

Synthesis and Magnetic Properties of the Multiferroic [C(NH2)3]Cr(HCOO)3 Metal-Organic Framework: The Role of Spin-Orbit Coupling and Jahn-Teller Distortions

We report for the first time the synthesis of [C(NH2)3]Cr(HCOO)3 stabilizing Cr2+ in formate perovskite, which adopts a polar structure and orders magnetically below 8 K. We discuss in detail the magnetic properties and their coupling to the crystal structure based on first-principles calculations, symmetry, and model Hamiltonian analysis. We establish a general model for the orbital magnetic moment of [C(NH2)3]M(HCOO)3 (M = Cr, Cu) based on perturbation theory, revealing the key role of the Jahn-Teller distortions. We also analyze their spin and orbital textures in k-space, which show unique characteristics.

Perovskite-derived structure modulation in the iron sulfate family

We report the first example of a perovskite sulfate [Na₃(H₂O)]Fe(SO₄)₃. Further structure modulation, by dimensional reduction or ligand extension, has resulted in two related layered perovskite-like compounds Na₆Fe(SO₄)₄ and Na₁₂Fe₃(SO₄)₆F₈. Taken together, these results open up a more general strategy for the future design of more complex perovskite-related materials.