Magnetic Coupling and Slow Relaxation of Magnetization in Chain-Based MnII, CoII, and NiII Coordination Frameworks

Tuning Dimensions of Complexes through Selective In Situ Reaction, Mechanistic Insights into Ni(II)-Catalyzed Br-OH Exchange, Magnetic Properties, and Density Functional Theory Studies

Two coordination polymers (CPs), namely, [Mn₃(L)₂(4,4'-bipy)₂(H₂O)₂]_n (1) and [Ni(L₁)(1,4-bib)(H₂O)]_n (2) (H₃L = 5-(3-bromo-4-carboxyphenoxy)isophthalic acid, H₂L₁ = 5-(3-hydroxyphenoxy)isophthalic acid, 4,4'-bpy = 4,4'-bipyridine, and 1,4-bib = 1,4-bis(1H-imidazol-1-yl)benzene), were synthesized under hydrothermal conditions. Most notably, with the help of the bromine atom-inducing effect, ligand transformation was observed in the structure of complex 2, which was scrutinized thoroughly by single crystal X-ray crystallography and X-ray photoelectron spectroscopy (XPS). Strikingly, Ni(II) ions were utilized as both coordinated atoms and as a catalyst for in situ Br-OH exchange of H₃L in the process, as a result of which the product would have preferred to form a one-dimensional chain. The same reaction cannot happen in 1, leading to form a two-dimensional structure. Moreover, Ni(II)-catalyzed and magnetic exchange mechanisms were well interpreted using density functional theory (DFT) calculations. Finally, complexes 1-2 show three-dimensional (3D) supramolecular structures because of intermolecular weak interactions (C-Br···π, C-H···π, C-H···O, and π···π stacking) and exhibit utterly different antiferrimagnetic coupling interactions.

Guest-Induced Switching of a Molecule-Based Magnet in a 3d-4f Heterometallic Cluster-Based Chain Structure

With the motivation of controlling a magnetic switch by external stimuli, we report here an infinite chain structure formed from the secondary building units of Cu₃Tb₂ clusters through the linkage of nitrate ions. It behaves as a molecule-based magnet with the highest energy barrier among isolated Tb/Cu-based single-molecule magnets and single-chain magnets, which is close to a dimer of a Cu₃Tb₂ cluster unit from a magnetic point as revealed by its correlation length of 2.23 Cu₃Tb₂ units. This kind of molecule-based magnet in a chain structure is rare. The removal of its guest ethanol molecules leads to the complete disappearance of slow magnetic relaxation behavior. Interestingly, the capture and removal of guest ethanol molecules are reversible, mediating a rare ON/OFF switching of a 3d-4f heterometallic molecule-based magnet, which was interpreted by the theoretical calculations based on the structural difference upon desolvation.

Single-chain magnets assembled in cobalt(ii) metal–organic frameworks

This feature article discusses the advantages, progress and prospects of constructing single-chain magnets in metal–organic frameworks.

Five new coordination polymers with a Y-shaped N-heterocyclic carboxylic acid: structural diversity, bifunctional luminescence sensing and magnetic properties

Five novel CPs have been synthesized under solvothermal conditions. The results show that 1 and 2 present high sensing ability for NACs and Fe³⁺ ions, and there exist ferromagnetic interaction in 3/4 and antiferromagnetic interaction in 5.

Mixed metal CoII1−xZnIIx–organic frameworks based on chains with mixed carboxylate and azide bridges: magnetic coupling and slow relaxation

A series of isomorphous three-dimensional metal–organic frameworks [Co^II_1−xZn^II_x(L)(N₃)]·H₂O (x = 0.26, 0.56 and 0.85) based on bimetallic Co^II_1−xZn^II_x (x = 0.26, 0.56 and 0.85) chains with random metal sites have been synthesized and magnetically characterized. The Co^II_1−xZn^II_x series, which intrinsically feature random anisotropic/diamagnetic sites, shows complex magnetic interactions. By gradually introducing the diamagnetic Zn^II ions into the pure anisotropic Co^II single-chain magnets system, the ferromagnetic interactions between Co^II ions are gradually diluted. Moreover, the slow magnetic relaxation behaviour of the mixed metal Co^II_1−xZn^II_x systems also changes. In this bimetallic series Co^II_1−xZn^II_x, the Co-rich materials exhibit slow relaxation processes that may arise from SCM mechanism, while the Zn^II-rich materials show significantly low slow magnetic relaxation. A general trend is that the activation energy and the blocking temperature decrease with the increase in diamagnetic Zn^II content, emphasizing the importance of anisotropy for slow relaxation of magnetization.

A series of mixed-metal systems consisting of Co^II_1−xZn^II_x chains with (μ-COO)₂(μ-EO-N₃) bridges were prepared, exhibiting interesting magnetic coupling and slow magnetic relaxation.

Random mixed-metal Co1−xNix single-chain magnets with simultaneous azide, carboxylate and tetrazolate bridges

A series of MOFs based on random ferromagnetic Co_1−xNi_x chains with simultaneous azide, carboxylate and tetrazolate bridges show metamagnetism and slow magnetic relaxation with complicated composition dependence and synergistic effects on single-chain slow dynamics.

Five Co(ii) coordination polymers with different counter anions based on [3,5-di(4H-1,2,4-triazol-4-yl)benzoato]− ligand: directed synthesis, structures and magnetic properties

Five cobalt(ii) coordination polymers were synthesized by reactions of HL with varied cobalt(ii) salts and different templates under solvothermal conditions.

Single-Chain Magnets Based on Octacyanotungstate with the Highest Energy Barriers for Cyanide Compounds

By introducing large counter cations as the spacer, two isolated 3, 3-ladder compounds, (Ph₄P)[Co^II(3-Mepy)_2.7(H₂O)_0.3W^V(CN)₈]·0.6H₂O (1) and (Ph₄As)[Co^II(3-Mepy)₃W^V(CN)₈] (2, 3-Mepy = 3-methylpyridine), were synthesized and characterized. Static and dynamic magnetic characterizations reveal that compounds 1 and 2 both behave as the single-chain magnets (SCMs) with very high energy barriers: 252(9) K for 1 and 224(7) K for 2, respectively. These two compounds display the highest relaxation barriers for cyano-bridged SCMs and are preceded only by two cobalt(II)-radical compounds among all SCMs. Meanwhile, a large coercive field of 26.2 kOe (1) and 22.6 kOe (2) were observed at 1.8 K.

Azide-bridged Cu(ii), Mn(ii) and Co(ii) coordination polymers constructed with a bifunctional ligand of 6-(1H-tetrazol-5-yl)-2,2′-bipyridine

Three new azide-bridged coordination polymers, [M(N₃)(tzbp)]_n (M = Cu, 1·Cu; Mn, 2·Mn; Co, 3·Co), were successfully prepared by introducing a bifunctional tetrazolate/2,2′-bipyridine ligand, 6-(1H-tetrazol-5-yl)-2,2′-bipyridine (Htzbp).

Biphenyl-2,4,6,3',5'-pentacarboxylic acid as a tecton for six new Co(II) coordination polymers: pH and N-donor ligand-dependent assemblies, structure diversities and magnetic properties

Six new Co(ii)-based mixed-ligand coordination polymers, namely, [Co2(H3bppc)2(2,2'-bpy)4]·H2O (), [Co2(Hbppc)(2,2'-bpy)2(H2O)]·H2O (), [Co(H2bppc)(H-bpp)]·2H2O (), [Co3(μ3-OH)(bppc)(dps)(CH3CH2OH)]·4H2O (), [Co2(bppc)(bib)(H2O)4]·(H2-bib)0.5·(H2O)3 (), and [Co2(Hbppc)(bix)2]·2H2O (), (H5bppc = biphenyl-2,4,6,3',5'-pentacarboxylic acid, 2,2'-bpy = 2,2'-bipyridine, bpp = 1,3-bis(4-pyridyl)propane, dps = 4,4'-sulfanediyldipyridine, bib = 1,4-bis(imidazol-1-yl)benzene, bix = 1,4-bis(imidazol-1-ylmethyl)benzene), have been obtained under solvothermal conditions. exhibits a 3D supramolecular framework based on a [Co2(H3bppc)2(2,2'-bpy)4] unit. has a (3,4)-connected dmc net with a (4·8(2))(4·8(5)) topology containing alternate binuclear metal clusters and single metal centres. shows a 3D supramolecular architecture constructed from ladder-like arrays decorated with H-bpp. exhibits a binodal (5,7)-connected 3D network based on trinuclear [Co3(μ3-OH)](5+) units with an unusual (3·4(6)·5(2)·6)(3(2)·4(6)·5(7)·6(5)·7) topology. features a (4,6)-connected 3D fsc open framework with binuclear [Co2(H2O)(COO)](3+) units as nodes, and H2-bib and water molecules located in the voids of its framework by hydrogen bonds. possesses a 3D net containing unusual 2D polyrotaxane sheets. Topological analysis reveals that has a (3,4,4)-connected 3D network with a (4·6·7(4))(4·6·7)(6·7(2)·10(2)·11) topology. The structural difference of and is due to the different pH values of the reaction system. Though complexes were synthesised under similar reaction conditions, the carboxylic groups of H5bppc were partially deprotonated in , and and fully deprotonated in and . Complexes display diverse structures depending on different N-donor ligands and the coordination modes of the multicarboxylate ligand. Variable-temperature magnetic susceptibility measurements reveal that complexes show antiferromagnetic interactions.

Two water-bridged cobalt(ii) chains with isomeric naphthoate spacers: from metamagnetic to single-chain magnetic behaviour

Two water-bridged cobalt(ii) chains with isomeric naphthoate spacers exhibit metamagnetic and SCM behaviours, arising from the dramatically different interchain stacking induced by naphthoate isomers.

Synthesis, structures and magnetic properties in 3d-electron-rich isostructural complexes based on chains with sole syn–anti carboxylate bridges

A series of isostructures based on 2,2′,4,4′-biphenyltetracarboxylic acid have been synthesized via solvothermal reaction, whereas magnetic studies reveal the polymers with sole syn–anti carboxylate bridges show different magnetic behaviors of uniform chains.