Influence of the Synthesis and Crystallization Processes on the Cation Distribution in a Series of Multivariate Rare-Earth Metal–Organic Frameworks and Their Magnetic Characterization

Abstract

The incorporation of multiple metal atoms in multivariate metal–organic frameworks is typically carried out through a one-pot synthesis procedure that involves the simultaneous reaction of the selected elements with the organic linkers. In order to attain control over the distribution of the elements and to be able to produce materials with controllable metal combinations, it is required to understand the synthetic and crystallization processes. In this work, we have completed a study with the RPF-4 MOF family, which is made of various rare-earth elements, to investigate and determine how the different initial combinations of metal cations result in different atomic distributions in the obtained materials. Thus, we have found that for equimolar combinations involving lanthanum and another rare-earth element, such as ytterbium, gadolinium, or dysprosium, a compositional segregation takes place in the products, resulting in crystals with different compositions. On the contrary, binary combinations of ytterbium, gadolinium, erbium, and dysprosium result in homogeneous distributions. This dissimilar behavior is ascribed to differences in the crystallization pathways through which the MOF is formed. Along with the synthetic and crystallization study and considering the structural features of this MOF family, we also disclose here a comprehensive characterization of the magnetic properties of the compounds and the heat capacity behavior under different external magnetic fields.

Magnetoelastic Coupling and Cryogenic Magnetocaloric Effect in Two-Site Disordered GdSrCoFeO6 Double Perovskite

“…The C latt fitting by eq is shown as a green line in Figure d. In the C mag ( T ) curve, two broad and well-defined peaks are centered on ∼10 and 70 K. The first one matches very well with the Schottky anomaly related mostly to Gd ions, whereas the second can be associated with the magnetic transition of FM/FiM to PM order. Generally, the materials with atoms with f -electrons have this anomalous peak of low-temperature specific heat.…”

“…Generally, the materials with atoms with f -electrons have this anomalous peak of low-temperature specific heat. The Schottky model explains this phenomenon through statistical physics by considering a few-level system with thermal occupation, , as C Sch ( T ) = R T 2 [ ∑ ν i Δ i 2 e − Δ i / T ∑ ν i e − Δ i / T − ( ∑ ν i Δ i e − Δ i / T ∑ ν i e − Δ i / T ) 2 ] . The model has energy gaps Δ i (in K units) as free parameters, Δ 0 = 0 corresponds to the ground level), while the number and degeneracy of levels ν i are fixed, leaving only one fitting parameter for 2-level systems.…”

The Chemistry of Metal Organic Framework Materials

“…More recently, MOF glasses, a disordered form of MOFs, are finding niche applications. This virtual collection catalogues recent MOF advances featured in Chemistry of Materials from 2022 to 2023, − with an accompanying editorial by Laura Gagliardi and Omar Yaghi that outlines three critical future directions for MOFs …”

“…17 Vasile et al scrutinized rare earth magnets created by a multivariate MOF strategy, revealing that phase segregation is observed for selected lanthanide combinations even for structures that appear to have a homogeneous distribution of multiple metals when examined as a single crystal; this finding was attributed to the differences in crystallization pathways. 18 Magnetic Kagome lattices are tremendously interesting but rare in MOFs. Clark and coworkers describe a family of copper carbonate based pillaredlayered ferromagnetic−antiferromagnetic Kagome networks which could represent important models for pursuing novel quantum and topological states of matter.…”

Discovery and In Situ Crystallization Studies of Cerium-Based Metal–Organic Frameworks with V-Shaped Linker Molecules

“…While only the crystal structure of La-RPF-4 was fully resolved, all compounds were tested for their potential use in luminescent and catalytic applications. In addition, the magnetic properties of mixed-metal MOFs with this structure type were investigated in a follow-up study …”