Magnetic Structures of Heterometallic M(II)–M(III) Formate Compounds

Low-dimensional metal-organic frameworks: a pathway to design, explore and tune magnetic structures

The magnetic structure adopted by a material relies on symmetry, the hierarchy of exchange interactions between magnetic ions and local anisotropy. A direct pathway to control the magnetic interactions is to enforce dimensionality within the material, from zero-dimensional isolated magnetic ions, one-dimensional (1D) spin-chains, two-dimensional (2D) layers to three-dimensional (3D) order. Being able to design a material with a specific dimensionality for the phenomena of interest is non-trivial. While many advances have been made in the area of inorganic magnetic materials, organic compounds offer distinct and potentially more fertile ground for material design. In particular magnetic metal-organic frameworks (mMOFs) combine magnetism with non-magnetic property functionality on the organic linkers within the structural framework, which can further be tuned with mild perturbations of pressure and field to induce phase transitions. Here, it is examined how neutron scattering measurements on mMOFs can be used to directly determine the magnetic structure when the magnetic ions are in a 2D layered environment within the wider 3D crystalline framework. The hydrated formate, in deuterated form, Co(DCOO)2·2D2O, which was one of the first magnetic MOFs to be investigated with neutron diffraction, is reinvestigated as an exemplar case.

Perusal on the role of DMF solvent and hydrogen bonding in the formation of 1D polymeric chains in mixed ligand Ni(II) complex as an anticancer agent: a computational approach

A novel mixed ligand Ni(II) metal complex has been investigated for the modification in structural conformation, coordination bond, and noncovalent interactions. The novel Ni(II) metal complex [Ni(TFPB)2(1,10-Ph)(DMF)] has been synthesized and structurally characterized, which featured six coordination with three bidentate ligands connected through oxygen and nitrogen atoms. The single-crystal X-ray analysis showed that the compound possessed octahedral geometry and C-H…F, C-H…O, and π…π intermolecular interactions resulting in the formation of supramolecular architecture contributed significantly towards the crystal packing and molecular stability. Hirshfeld surface analysis was carried out to validate various intermolecular interactions. Further, the 3D structural topologies were visualized using energy framework analysis. To explore the coordination stability and chemically reactive parameters of the novel Ni(II) complex, the electronic structure was optimized using density functional theory calculations. The natural bond orbital analysis revealed the various hyperconjugative interactions exhibited by the complex. In addition, the complex was screened for in silico studies to understand the antitumoricidal potential of the novel Ni(II) complex. Molecular docking studies were also performed against three targeted proteins (PDB ID: 6H0W, 6NE5, and 6E91) to investigate the binding mode and protein-ligand interactions. These results are further analyzed by molecular dynamic simulation to confirm the best possible interactions and stability in the active site of the targeted proteins with a simulation period of 100 ns.Communicated by Ramaswamy H. Sarma.

Magnetic order in a metal thiocyanate perovskite-analogue

Metal thiocyanate perovskite-analogues are a growing class of materials, but although they contain paramagnetic cations there have been no reports of their magnetic properties. Due to the large separations between...

Structures and magnetic properties of two heterometallic Cu(ii)–Cd(ii) polymers exhibiting antiferromagnetic ordering

Two heterometallic Cu(ii)–Cd(ii) polymers (1 and 2) with a 2D layer or 1D chain structure were obtained and their magneto-structural correlations were discussed, and 1 displayed antiferromagnetic ordering at lower temperature.

Inorganic-Organic Hybrid Molecular Materials: From Multiferroic to Magnetoelectric

Inorganic-organic hybrid molecular multiferroic and magnetoelectric materials, similar to multiferroic oxide compounds, have recently attracted increasing attention because they exhibit diverse architectures, a flexible framework, fascinating physics, and potential magnetoelectric functionalities in novel multifunctional devices such as energy transformation devices, sensors, and information storage systems. Herein, the classification of multiferroicity and magnetoelectricity is briefly outlined and then the recent advances in the multiferroicity and magnetoelectricity of inorganic-organic hybrid molecular materials, particularly magnetoelectricity and the relevant magnetoelectric mechanisms and their categories are summarized. In addition, a personal perspective and an outlook are provided.

First-principles study of the structural, electronic, magnetic, and ferroelectric properties of a charge-ordered iron(ii)-iron(iii) formate framework

Density functional theory calculations have been performed for the structural, electronic, magnetic, and ferroelectric properties of a mixed-valence Fe(ii)-Fe(iii) formate framework [NH₂(CH₃)₂][FeⁱⁱⁱFeⁱⁱ(HCOO)₆]. Recent experiments report a spontaneous electric polarization, and our calculations are in agreement with the reported experimental value. Furthermore, we shed light onto the microscopic mechanism leading to the observed value, as well as on how to possibly enhance the polarization. The interplay between charge ordering, dipolar ordering of DMA⁺ cations, and the induced structural distortions suggest new interesting directions to explore in these complex multifunctional hybrid perovskites.

Tunable Ferromagnetic Strength in Niccolite Structural Heterometallic Formate Framework Based on Orthogonal Magnetic Orbital Interactions

A series of heterometallic formate framework templated by amines were solvothermally prepared. They feature the formula of [A^I][CrM^II(HCO₂)₆] (A^I = NH₄H₂O^I and M = Mn for 1, A^I = CH₃NH₃^I and M = Fe for 2, A^I = CH₃NH₂CH₃^I and M = Co for 3, A^I = CH₃NH₃^I and M = Ni for 4). The title compounds exhibit isostructural niccolite architectures with differences only in the host metal ions and guest amines. Tunable ferromagnetic (FO) strength was realized in the resulting framework under the guidance of orthogonal magnetic orbital analysis of Cr^III (t_2g³e_g) and M^II (t_2g³e_g² for Mn^II, t_2g⁴e_g² for Fe^II, t_2g⁵e_g² for Co^II, t_2g⁶e_g² for Ni^II) ions. The magnetic ordering temperatures derived from the experimental magnetic measurements for 1-4 are lower than 2, 10.3, 7.6, and 22.0 K, respectively. Notably, thanks to the weak FO coupling between Cr^III and Mn^II ions, compound 1 displays a large magnetocaloric effect bearing the maximum of magnetic entropy change (-Δ S_m^max) up to 43.9 J kg^-1 K^-1 with Δ H = 7 T and T = 3.5 K, larger than most reported transition metal-based complexes and commercial gadolinium gallium garnet (Gd₃Ga₅O₁₂) (-Δ S_m^max = 38.4 J kg^-1 K^-1 with Δ H = 7 T). From 1, 2/3, to 4, an enhancement of the magnetic ordering temperature is observable due to the increasing strength of FO interactions between Cr^III and M^II ions. Our work provides a successful instance to modulate the strength of FO exchange via analyzing the orthogonal magnetic orbitals of heterometallic ions.

Two 1D carboxylate-bridged magnets displaying solvent-dependent canted antiferromagnetic ordering

Two 1D carboxylate-bridged chain complexes can be converted irreversibly from 1 to 2 and exhibit terminal solvent-dependent canted antiferromagnetic ordering with T_C = 38 K.

Pressure dependence of spin canting in ammonium metal formate antiferromagnets

High-pressure single-crystal X-ray diffraction at ambient temperature and high-pressure SQUID measurements down to 2 K were performed up to ∼2.5 GPa on ammonium metal formates, [NH₄][M(HCOO)₃] where M = Mn²⁺, Fe²⁺, and Ni²⁺, in order to correlate structural variations to magnetic behaviour. Similar structural distortions and phase transitions were observed for all compounds, although the transition pressures varied with the size of the metal cation. The antiferromagnetic ordering in [NH₄][M(HCOO)₃] compounds was maintained as a function of pressure, and the magnetic ordering transition temperature changed within a few kelvins depending on the structural distortion and the metal cation involved. These compounds, in particular [NH₄][Fe(HCOO)₃], showed greatest sensitivity to the degree of spin canting upon compression, clearly visible from the twenty-fold increase in the low-temperature magnetisation for [NH₄][Fe(HCOO)₃] at 1.4 GPa, and the change from purely antiferromagnetic to weakly ferromagnetic ordering in [NH₄][Mn(HCOO)₃] at 1 GPa. The variation in the exchange couplings and spin canting was checked with density-functional calculations that reproduce well the increase in canted moment within [NH₄][Fe(HCOO)₃] upon compression, and suggest that the Dzyaloshinskii-Moriya (DM) interaction is evolving as a function of pressure. The pressure dependence of spin canting is found to be highly dependent on the metal cation, as magnetisation magnitudes did not change significantly for when M = Ni²⁺ or Mn²⁺. These results demonstrate that the overall magnetic behaviour of each phase upon compression was not only dependent on the structural distortions but also on the electronic configuration of the metal cation.

Probing magnetic interactions in metal-organic frameworks and coordination polymers microscopically

Materials with magnetic interactions between their metal centres play a tremendous role in modern technologies and can exhibit unique physical phenomena. In recent years, magnetic metal-organic frameworks and coordination polymers have attracted significant attention because their unique structural flexibility enables them to exhibit multifunctional magnetic properties or unique magnetic states not found in the conventional magnetic materials, such as metal oxides. Techniques that enable the magnetic interactions in these materials to be probed at the atomic scale, long established to be key for developing other magnetic materials, are not well established for studying metal-organic frameworks and coordination polymers. This review focuses on studies where metal-organic frameworks and coordination polymers have been examined using such microscopic probes, with a particular focus on neutron scattering and density-functional theory, the most-well established experimental and computational techniques for understanding magnetic materials in detail. This paper builds on a brief introduction to these techniques to describe how such probes have been applied to a variety of magnetic materials starting with select historical examples before discussing multifunctional, low dimensional and frustrated magnets. This review highlights the information that can be obtained from such microscopic studies, including the strengths and limitations of these techniques. The article then concludes with a brief perspective on the future of this area.

Tuning the structure and properties of a multiferroic metal–organic-framework via growing under high magnetic fields

High magnetic field-induced synthesis has been demonstrated to tune the structure and properties of the multiferroic metal–organic framework [(CH₃)₂NH₂][Mn(HCOO)₃].

Ferroelastic Phase Transition and Switchable Dielectric Constant in Heterometallic Niccolite Formate Frameworks

Four heterometallic formate frameworks templated by various alkylamine cations with the general formula [cat][Ga^IIIMn^II(HCOO)₆] {cat is MA (CH₃NH₃⁺) for 1, DMA [(CH₃)₂NH₂⁺] for 2, EtA (CH₃CH₂NH₃⁺) for 3, and DEtA [(CH₃CH₂)₂NH₂⁺] for 4} have been prepared and characterized by X-ray diffraction, differential scanning calorimetry, and dielectric studies. All of the complexes have niccolite-like structures, which possess the same [GaMn(HCOO)₆]^- anionic framework with binodal (4¹²·6³)(4⁹·6⁶) topology; only the counterions in the cavity are different. Complex 4 undergoes a reversible ferroelastic phase transition around 220 K accompanied by a thermally switchable dielectric constant transition triggered by the freezing of the order-disorder DEtA cations.

A Niccolite Structural Multiferroic Metal-Organic Framework Possessing Four Different Types of Bistability in Response to Dielectric and Magnetic Modulation

Multiple switchable physical properties have been demonstrated in one single niccolite structural metal-organic framework, [(CH₃ CH₂ )₂ NH₂ ][Fe^III Fe^II (HCOO)₆ ] (1), including (i) a reversible ferroelastic phase transition triggered by freezing the disordered (CH₃ CH₂ )₂ NH₂⁺ cations, (ii) a thermally switchable dielectric constant transition accompanied by phase transition, and (iii) thermal and positive magnetic field driven magnetic poles reversal at low temperatures, attributed to different responses of the magnetization of Fe^II and Fe^III sublattices to external stimuli. More interestingly, the exchange anisotropy between the two sublattices can also give rise to tunable positive and negative exchange bias fields. Straightforwardly, such diverse demonstrations of bistability in one single material (depending on the specific tuning way) will provide extra freedom and flexibility for the design of switcher devices.

Study of the relationship between magnetic field and dielectric properties in two ferromagnetic complexes

Two heterometallic niccolite structure frameworks [NH₂(CH₃)₂][Cr^IIIM^II(HCOO)₆] (M = Fe, Ni) were reported and characterized by single crystal X-ray diffraction, dielectric and magnetic susceptibility measurement.

Four coordination polymers based on dinuclear and trinuclear units with a new multifunctional pyridyl-dicarboxylate ligand: luminescence and magnetic properties

Four coordination polymers with a new pyridyl-dicarboxylate ligand were synthesized under solvothermal conditions and studied by means of X-ray crystallography, topological analyses, luminescence and magnetic analyses.