The magnet-like behavior can beobserved by slow relaxation of the magnetization below theblocking temperature. Since the discovery of SMMs in theearly 1990s, this assumption has formed the basis for theunderstanding of the origin of the anisotropic barrier.However, in recent years the development of novel lantha-nide-only SMMs that challenge and defy this theory pose anumber of questions:

A Polynuclear Lanthanide Single-Molecule Magnet with a Record

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

Among the recent developments in metal-organic frameworks (MOFs), porous layered coordination polymers (CPs) have garnered attention due to their modular nature and tunable structures. These factors enable a number of properties and applications, including gas and guest sorption, storage and separation of gases and small molecules, catalysis, luminescence, sensing, magnetism, and energy storage and conversion. Among MOFs, two-dimensional (2D) compounds are also known as 2D CPs or 2D MOFs. Since the discovery of graphene in 2004, 2D materials have also been widely studied. Several 2D MOFs are suitable for exfoliation as ultrathin nanosheets similar to graphene and other 2D materials, making these layered structures useful and unique for various technological applications. Furthermore, these layered structures have fascinating topological networks and entanglements. This review provides an overview of different aspects of 2D MOF layered architectures such as topology, interpenetration, structural transformations, properties, and applications.

Two-Dimensional Metal-Organic Framework Materials: Synthesis, Structures, Properties and Applications.

Single-chain magnets (SCMs) are one-dimensional (1D) slow-relaxing magnetic chains with interesting fundamental properties and applications, such as information storage. The mechanism underlying the slow relaxation of SCMs is Glauber dynamics, in which R. J. Glauber proposed about 50 years ago that the 1D correlation of ferromagnetically coupled Ising spins causes very slow magnetic relaxation at a finite temperature. Since the first experimental observation of SCM dynamics of a cobalt(II)–organic radical alternating chain in 2001, several SCM systems have been reported, supporting and expanding the Glauber model. In this review, we present the recent advances concerning SCMs with the main focus on SCM systems beyond the Ising limit, SCMs constructed with non-collinear or canted antiferromagnetic intrachain interactions, the relation between SCM dynamics and interchain interactions, and some SCMs with chirality, porosity, spin-crossover, photo-switchable states, and so on.

Single-chain magnets: beyond the Glauber model

Five new MnII coordination polymers, namely [Mn2(tbip)2(bix)] (1), [Mn3(tbip)3(bix)2] (2), [Mn3(tbip)2(Htbip)2(bib)2]·4H2O (3), [Mn4(tbip)4(bbp)2(H2O)2] (4), and [Mn4(tbip)4(bip)]·2H2O (5), were prepared by hydrothermal reactions of Mn(II) acetate with H2tbip (5-tert-butyl isophthalic acid) in the presence of different di-imidazolyl coligands (bix =1,4-bis(imidazol-1-ylmethyl)benzene, bib =1,4-bis(imidazol) butane, bbp =1,3-bis(benzimidazol)propane, bip =1,3-bis(imidazol)propane). All complexes were characterized by elemental analysis, IR spectra, thermogravimetric analysis, single-crystal X-ray crystallography, and powder X-ray diffraction. Single crystal X-ray studies show that these coordination polymers contain homometallic clusters varying from dimeric, trimeric, and tetrameric motifs to polymeric chains depending upon the coligands used. Complex 1 has a 3D 6-connected polycatenane network with dinuclear [Mn2O2] secondary building units. Complex 2 possesses a 3D 8-connected structure with trinuclear ...

MnII Coordination Polymers Based on Bi-, Tri-, and Tetranuclear and Polymeric Chain Building Units: Crystal Structures and Magnetic Properties

Metamagnetism and slow magnetic dynamics in an antiferromagnet composed of cobalt(II) chains with mixed azide-carboxylate bridges.

The reactions of manganese(II) acetate or perchlorate, sodium azide, and the inner-salt-type dicarboxylate ligand 1,3-bis(4-carboxylato-1-pyridinium)propane (L) under different conditions yielded four different MnII coordination polymers with mixed azide and carboxylate bridges: {[Mn(L)(N3)]ClO4·0.5H2O}n (1), {[Mn2(L)2(N3)2][Mn(N3)4(H2O)2]·2H2O}n (2), {[Mn2(L)2(N3)2(H2O)2]Br(N3)·2H2O}n (3), and [Mn4 (L)2(N3)8]n (4). The compounds exhibit great diversity in their structures and magnetic properties. Both 1 and 2 contain anionic chains featuring a mixed (OCO)2(EO-N3) triple bridge (EO = end-on) between adjacent MnII ions. In 1, two independent sets of triple bridges with apparently different structural parameters alternate in the AABB sequence, and the resulting alternating chains are cross-linked into a cationic 3D framework by the cationic dipyridinium spacers. Differently, the chains in 2 have uniform bridges and are interlinked into a 2D coordination layer. An expression of the magnetic susceptibility fo...

Diverse manganese(II) coordination polymers with mixed azide and zwitterionic dicarboxylate ligands: structure and magnetic properties.

Mn(II) and Fe(II) compounds derived from azide and the zwitterionic 1-carboxylatomethylpyridinium-4-carboxylate ligand are isomorphous three-dimensional metal-organic frameworks (MOFs) with the sra net, in which the metal ions are connected into anionic chains by mixed (μ-1,1-azide)bis(μ-carboxylate) triple bridges and the chains are cross-linked by the cationic backbones of the zwitterionic ligands. The Mn(II) MOFs display typical one-dimensional antiferromagnetic behavior. In contrast, with one more d electron per metal center, the Fe(II) counterpart shows intrachain ferromagnetic interactions and slow relaxation of magnetization attributable to the single-chain components. The activation energies for magnetization reversal in the infinite- and finite-chain regimes are Δτ1 = 154 K and Δτ2 = 124 K, respectively. Taking advantage of the isomorphism between the Mn(II) and Fe(II) MOFs, we have prepared a series of mixed-metal Mn(II)(1-x)Fe(II)(x) MOFs with x = 0.41, 0.63, and 0.76, which intrinsically feature random isotropic/anisotropic sites and competing antiferromagnetic-ferromagnetic interactions. The materials show a gradual antiferromagnetic-to-ferromagnetic evolution in overall behaviors as the Fe(II) content increases, and the Fe-rich materials show complex relaxation processes that may arise for mixed SCM and spin-glass mechanisms. A general trend is that the activation energy and the blocking temperature increase with the Fe(II) content, emphasizing the importance of anisotropy for slow relaxation of magnetization.

Manganese(II), iron(II), and mixed-metal metal-organic frameworks based on chains with mixed carboxylate and azide bridges: magnetic coupling and slow relaxation.

Field-modified multiple slow relaxations in a metamagnet composed of cobalt(II) chains with mixed azide and tetrazolate bridges

Three isomorphous coordination polymers based on the chain with triple (μ-1,1-N3)(μ-1,3-COO)2 bridges have been synthesized from a new zwitterionic dicarboxylate ligand [L– = 1-(4-carboxylatobenzyl)pyridinium-4-carboxylate]. They are of formula [M(L)(N3)]n·3nH2O [M = MnII, CoII, and NiII]. In these compounds, the mixed-bridge chains are linked into 2D coordination networks by the N-benzylpyridinium spacers. The magnetic properties depend strongly on the nature of the metal center. The magnetic coupling through (μ-1,1-N3)(μ-1,3-COO)2 is antiferromagnetic in the MnII compound but ferromagnetic in the CoII and NiII analogues. Magnetostructural analyses indicate that the magnitude of the magnetic coupling can be correlated to the M–N–M angle of the azide bridge and the average M–O–C–O torsion angle of the carboxylate bridge. As the values of these parameters increase, the antiferromagnetic coupling for MnII decreases while the ferromagnetic coupling for CoII increases. With strong magnetic anisotropy, the CoI...

Kun Wang

Papers

Metamagnetism and slow magnetic dynamics in an antiferromagnet composed of cobalt(II) chains with mixed azide-carboxylate bridges.

Diverse manganese(II) coordination polymers with mixed azide and zwitterionic dicarboxylate ligands: structure and magnetic properties.

Manganese(II), iron(II), and mixed-metal metal-organic frameworks based on chains with mixed carboxylate and azide bridges: magnetic coupling and slow relaxation.

Field-modified multiple slow relaxations in a metamagnet composed of cobalt(II) chains with mixed azide and tetrazolate bridges

Magnetic coupling and slow relaxation of magnetization in chain-based Mn(II), Co(II), and Ni(II) coordination frameworks.