Constructing magnetic molecular solids by employing three-atom ligands as bridges

Framework-structured weak ferromagnets are new rising stars in molecule-based magnetic materials. The framework structures are powerful carriers for long-range ordering of spins. And weak ferromagnetism due to spin canting is an effective approach for magnets because of its frequent occurrence and desired spontaneous magnetization as long as the canting angle γ is large enough. In this critical review, we provide an overview of the various framework-structured weak ferromagnets based on different grades of ligands (from mono-atom to three-atom-like ligands). Particular emphasis is given to the relationships between structural features and the properties, rational employment of the ligands, and weak ferromagnetic strategies for molecule-based magnets with exciting properties and applications (273 references).

Framework-structured weak ferromagnets

A toolbox of building blocks, linkers and crystallisation methods used to generate single-chain magnets

By employing a flexible molecule, 2,2′-dipyridylamine (dpa), as a bidentate coligand, three azide-bridged one-dimensional coordination polymers, [M(dpa)(N3)2]n (M = Cu, 1·Cu; Co, 2·Co) and [Ni(dpa)(OAc)0.5(N3)1.5(H2O)]n (3·Ni), have been successfully synthesized and structurally and magnetically characterized. They show versatile one-dimensional chain structures. 1·Cu is an EO-N3 bridged uniform chain; 2·Co is an alternative chain linked by two EO-N3 and two EE-N3 bridges. Interestingly, 3·Ni is a zigzag chain linked alternatively by one EE-N3 and a novel 3-fold bridge, which is composed of two EO-N3 and one acetate group. This series of azido complexes demonstrates that the flexibility of the dpa ligand plays an important role in directing the structures of the final products. Magnetic studies reveal dominant intrachain antiferromagnetic couplings in compound 1·Cu. Compounds 2·Co and 3·Ni are weak ferromagnets due to the spin canting, with critical temperatures of 12.4 and 32.5 K, respectively.

Diversity of azido magnetic chains constructed with flexible ligand 2,2'-dipyridylamine.

Two-step magnetic transitions: An azide-bridged 1D Mn(III) coordination polymer with a unique single end-on mode was prepared; it displayed atypical antiferromagnetic couplings and field-induced two-step magnetic transitions (see figure). The spin-canted phenomenon in the antiferromagnetic chain complex plays a pivotal role in establishing the slow magnetic relaxation.

An End‐On Azide‐Bridged Antiferromagnetic Single‐Chain Magnet Involving Spin Canting and Field‐Induced Two‐Step Magnetic Transitions

Low-dimensional magnetic compounds, especially zero-dimensional magnetic clusters and 1D chain compounds that show single-molecule and single-chain magnetic properties, are currently of ongoing interest for the design and synthesis of new molecule-based magnets. Well-documented examples include Mn12 [1] and Fe8 [2] for single-molecule magnets (SMMs), and [Co(hfacac)2(NITPhOMe)] (hfacac = hexafluoroacetylacetonate, NITPhOMe = 4′-methoxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and [Mn2(saltmen)2Ni(pao)2L2](A)2 (saltmen = N,N′-1,1,2,2-tetramethylethylenebis(salicylideneiminate), pao = pyridine-2-aldoximate, and A= anion) for single-chain magnets (SCMs). Although they are not associated with real 3D magnetic order, the slow magnetic relaxation and a hysteresis loop below the blocking temperature make them behave like classical magnets, and good candidates for potential high-density information storage. The slow relaxation phenomenon, which is one of the main characters for both SMMs and SCMs, is quite common for many systems, including magnetic systems, liquid crystals, polymers, high-critical-temperature (Tc) superconductors, and metallic glasses. Typical examples of magnetic systems, besides SMMs and SCMs, are spin-glass magnets, cluster spin-glass magnets, and classical superparamagnets. The origin of the relaxation is quite complex and varies in different systems. Randomness (defects, disorder, etc.) and frustration (geometrical or competitive) are thought to be responsible for the spin-glass system. For SMMs and SCMs, the strong uniaxial magnetic anisotropy (where the zero-field splitting parameter D < 0) and the large spin values of the ground states (for SCMs, one can say that the total spin number ST =∞) are two main reasons for the very slow relaxation in these systems. In long-range ordered magnets, such as ferromagnets or ferrimagnets, the relaxation can also be induced by the dynamics of domain walls, such as domain-wall displacement and the domain magnetization rotation and so on. In order to obtain a magnetic ground-state for a chain, individual magnetic moments cannot cancel out. This condition can be satisfied if the chain is ferromagnetic (e.g., [[FeL(CN)4]4Co(H2O)x] (L= 2,2′-bipyridine or 1,10-phenanthroline, x = 1 or 2), and [Co(bt)(N3)2] (bt = 2,2′-bithiazoline)) or ferrimagnetic, such as [Co(hfacac)2(NITPhOMe)]. [3a] There is another way to achieve this goal in an antiferromagnetic chain: the spin-canting that arises from the non-colinear spin arrangements because of the existence of an antisymmetrical component of the superexchange interaction (Dzyaloshinsky– Moriya interaction, DMI) or the appropriate anisotropy. Such is the case in the reported SCM of Co(H2L)(H2O) (H4L= 4-Me-C6H4-CH2N(CH2PO3H2)2). [3g]

Weak Ferromagnetism and Dynamic Magnetic Behavior in a Single End‐to‐End Azide‐Bridged Nickel(II) Chain

Five-fold twinned Ir-alloyed Pt nanorods with high C1 pathway selectivity for ethanol electrooxidation

Direct oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using O2 as the oxidant has crucial significance under mild conditions in industrial manufacturing. Herein, an efficient and ecofriendly Pd/O-g-C3N4 heterojunction catalyst using oxygen-doped g-C3N4 (O-g-C3N4) with a porous surface as the support is developed for visible light-driven thermocatalytic oxidation of BzOH to BzH by using O2 as the sole oxidant. The obtained Pd/O-g-C3N4 exhibits visible light-enhanced catalytic performance under visible light irradiation with BzOH conversion and BzH yield of 89.4 and 76.6%, respectively, which are 1.96 and 1.83 times higher than those for the catalyst in the dark. Oxygen doping, as well as Pd deposition, can significantly narrow the band gap of g-C3N4, thereby enhancing its visible light harvesting ability. The resulting heterojunction interface between Pd nanoparticles and O-g-C3N4 might promote separation of the photogenerated e--h+ pairs. In addition to achieving considerable BzOH conversion and BzH yield, Pd/O-g-C3N4 also exhibits impressive stability. The current study provides potential applications for the green and efficient catalytic oxidation of other alcohols to corresponding aldehydes using O2 as the oxidant.

Activating Pd Nanoparticles on Oxygen-Doped g-C3N4 for Visible Light-Driven Thermocatalytic Oxidation of Benzyl Alcohol.

Optimal Design of a Small-Molecule Crowding Electrolyte and Molecular Dynamics Simulation of an Electrode–Electrolyte Interface for Aqueous Supercapacitors with a Wide Operating Temperature Range

Isolation of light-switchable metal–organic cages within the targeted cavities of metal–organic frameworks through light-assisted precise size control, thus providing an efficient, light-switchable adsorbent for tunable CO2 adsorption.

https://pubs.rsc.org/en/content/articlepdf/2023/qi/d3qi00412k

Target-specific isolation of light-switchable metal–organic cages within metal–organic frameworks for tunable CO2 adsorption

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