Spin Canting and Metamagnetism in a 3D Homometallic Molecular Material Constructed by Interpenetration of Two Kinds of Cobalt(II)-Coordination-Polymer Sheets

Improvement of two Mn2+ coordination polymers on cognitive function of aged rats after anesthesia

Two Mn²⁺ coordination polymers (CPs) with the scientific terms of {[Mn(TTPA)·(H₂O)₂]·H₂O}_n (1) and {[Mn(TTPA)·(H₂TTPA)]·2DMSO}_n (2) were favorably created on the basis of multidentate linking organic ligand 2,5-bis-(1,2,4-triazol-1-yl)-terephthalic acid (H₂TTPA) in the conditions of solvent-presupposed thermal reaction. To measure the influence of two Mn²⁺ coordination polymers with novel structures, the ELISA assay and real-time RT-PCR assay were conducted in this present research. First of all, the ELISA assay was conducted to measure the content of inflammatory cytokines released into the hippocampal tissue. In addition to this, the relative expression of the TAU protein in the brain was further determined with real-time RT-PCR assay.

Melamine-induced synthesis of a structurally perfect kagomé antiferromagnet

We report here a structurally perfect kagomé lattice {[Cu₃(bpy)₆](SiF₆)₃(melamine)₈}_n (1), where bpy is 4,4'-bipyridine and [SiF₆]^2- is a hexafluorosilicate anion. In comparison to general 1D linear, 2D layered and 3D cubic metal-organic frameworks, by using Cu²⁺ nodes and bpy ligands, a perfect kagomé lattice was synthesized by introducing C₃ symmetrical melamine molecules. Magnetic susceptibility and low-temperature heat capacity measurements indicated weak antiferromagnetic interactions between the spins and no long-range magnetic ordering to 0.7 K. Using C₃ symmetrical melamine molecules can be considered as a challenging synthetic strategy to afford new topological materials.

A chromotropic PtIIPdIICoII coordination polymer with dual electrocatalytic activity for water reduction and oxidation

Here, we present a heterometallic coordination polymer that exhibits heterogeneous electrocatalytic activities for both water reduction and water oxidation. Treatment of the PtII2PdII2 tetranuclear complex [Pd₂{Pt(NH₃)₂(D-pen)₂}₂] ([1]; D-H₂pen = D-penicillamine) with CoX₂ (X = Cl, Br) provided (PtII2PdII2CoII2)_n coordination polymers [Co₂(H₂O)₆(1)]X₄ ([2]X₄), in which the PtII2PdII2 units of [1] are linked by [Co₂(μ-H₂O)(H₂O)₅]⁴⁺ moieties in a 3D network structure. [2]X₄ showed a colour change from orange to dark green upon dehydration, reflecting the geometrical conversion of the Co^II centres in [Co₂(μ-H₂O)(H₂O)₅]⁴⁺ from an octahedron to a tetrahedron by the removal of aqua ligands. While both [2]Cl₄ and [2]Br₄ electrochemically catalysed water reduction to H₂ in the solid state due to the presence of Pd^II active centres, water oxidation to O₂ was catalysed only by [2]Br₄, which is ascribed to the presence of Br^- ions that mediate the catalytic reactions that occurred at Co^II active centres.

3D Metal-Organic Frameworks Based on Co(II) and Bithiophendicarboxylate: Synthesis, Crystal Structures, Gas Adsorption, and Magnetic Properties

Three new 3D metal-organic porous frameworks based on Co(II) and 2,2′-bithiophen-5,5′-dicarboxylate (btdc²⁻) [Co₃(btdc)₃(bpy)₂]·4DMF, 1; [Co₃(btdc)₃(pz)(dmf)₂]·4DMF·1.5H₂O, 2; [Co₃(btdc)₃(dmf)₄]∙2DMF∙2H₂O, 3 (bpy = 2,2′-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformamide) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co₃(RCOO)₆}, connected either by btdc^2– ligands (1, 3) or by both btdc^2– and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N₂, O₂, CO, CO₂, CH₄ adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m²⋅g⁻¹ and promising gas separation performance with selectivity factors up to 35.7 for CO₂/N₂, 45.4 for CO₂/O₂, 20.8 for CO₂/CO, and 4.8 for CO₂/CH₄. The molar magnetic susceptibilities χ_p(T) were measured for 1 and 2 in the temperature range 1.77–330 K at magnetic fields up to 10 kOe. The room-temperature values of the effective magnetic moments for compounds 1 and 2 are μ_eff (300 K) ≈ 4.93 μ_B. The obtained results confirm the mainly paramagnetic nature of both compounds with some antiferromagnetic interactions at low-temperatures T < 20 K in 2 between the Co(II) cations separated by short pz linkers. Similar conclusions were also derived from the field-depending magnetization data of 1 and 2.

Discrete unusual mixed-bridged trinuclear CoIII2CoII and pentanuclear NiII coordination complexes supported by a phenolate-based ligand: theoretical and experimental magneto-structural study

We report a combined computational and experimental magnetostructural correlation in trinuclear mixed valence cobalt and pentanuclear nickel complexes.

Azido-Cyanide Mixed-Bridged FeIII-NiII Complexes

The successful introduction of azide ions as secondary bridges into the Fe^III-Ni^II cyanide system afforded two clusters and one unique 4(3),2-ribbon chain: [(bpzpy)₂Ni₂(μ₂-1,1-N₃)₂{(pzTp)Fe(CN)₃}₂]·3H₂O [1; bpzpy = 2,6-bis(pyrazol-1-yl)pyridine, and pzTp = tetrakis(pyrazolyl)borate], [(L1)₂Ni₄(μ₃-1,1,1-OCH₃)₂(μ₂-1,1-N₃)₂(H₂O)₂{(Tp)Fe(CN)₃}₂]·2CH₃OH·H₂O [2; Tp = hydrotris(pyrazolyl)borate, and HL1 = 2,6-bis{(2-hydroxypropylimino)methyl}-4-methylphenol], and [(L2)₂Ni₃(μ₂-1,1-N₃)₄{(pzTp)Fe(CN)₃}₂]_n (3; L2 = 2-{[phenyl(pyridin-2-yl)methylene]amino}ethan-1-amine). Both 1 and 2 feature the centrosymmetric {Fe^III-Ni^II₂-Fe^III} and {Fe^III-Ni^II₄-Fe^III} rodlike structures in which the two peripheral [(Tp^R)Fe(CN)₃]^- anions act as monodentate ligands via one cyanide group to link the central azide-bridged [Ni₂] and [Ni₄] subunit, respectively, while 3 displays an extended structure of the double-zigzag (4,2-ribbon) chain in which the double end-on azide-bridged trinuclear [Ni₃] subunits serve as the 4-connected nodes. Magnetic study revealed that intramolecular ferromagnetic coupling is dominated by the azide or cyanide bridges in all of the complexes. Remarkably, complex 1 behaves as a single-molecule magnet with an effective energy barrier of 16.5 cm^-1 at zero dc field, while complex 3 exhibits metamagnetism with a hidden spin canting property below 12 K.

Selective Metal-Ligand Bond-Breaking Driven by Weak Intermolecular Interactions: From Metamagnetic Mn(III)-Monomer to Hexacyanoferrate(II)-Bridged Metamagnetic Mn2Fe Trimer

Metal-ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare example where metal-ligand bonds dissociate in an irreversible way, helped by a large number of weak intermolecular interactions that surpass the energy of the metal-ligand bond. Thus, we describe the design and synthesis of trinuclear Mn₂Fe complex {[Mn(L)(H₂O)]₂Fe(CN)₆},^2- starting from a mononuclear Mn(III)-Schiff base complex: [Mn(L)(H₂O)Cl] (1) and [Fe(CN)₆]^4- anions. This reaction implies the dissociation of Mn(III)-Cl coordination bonds and the formation of Mn(III)-NC bonds with the help of several intermolecular interactions. Here, we present the synthesis, crystal structure, and magnetic characterization of the monomeric Mn(III) complex [Mn(L)(H₂O)Cl] (1) and of compound (H₃O)[Mn(L)(H₂O)₂]{[Mn(L)(H₂O)]₂Fe(CN)₆}·4H₂O (2) (H₂L = 2,2'-((1E,1'E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(4-methoxyphenol)). Complex 1 is a monomer where the Schiff base ligand (L) is coordinated to the four equatorial positions of the Mn(III) center with a H₂O molecule and a Cl^- ion at the axial sites and the monomeric units are assembled by π-π and hydrogen-bonding interactions to build supramolecular dimers. The combination of [Fe(CN)₆]^4- with complex 1 leads to the formation of linear Mn-NC-Fe-CN-Mn trimers where two trans cyano groups of the [Fe(CN)₆]^4- anion replace the labile chloride from the coordination sphere of two [Mn(L)(H₂O)Cl] complexes, giving rise to the linear anionic {[Mn(L)(H₂O)]₂Fe(CN)₆}^2- trimer. This Mn₂Fe trimer crystallizes with an oxonium cation and a mononuclear [Mn(L)(H₂O)₂]⁺ cation, closely related to the precursor neutral complex [Mn(L)(H₂O)Cl]. In compound 2, the Mn₂Fe trimers are assembled by several hydrogen-bonding and π-π interactions to frame an extended structure similar to that of complex 1. Density functional theoretical (DFT) calculations at the PBE1PBE-D3/def2-TZVP level show that the bond dissociation energy (-29.3 kcal/mol) for the Mn(III)-Cl bond is smaller than the summation of all the weak intermolecular interactions (-30.1 kcal/mol). Variable-temperature magnetic studies imply the existence of weak intermolecular antiferromagnetic couplings in both compounds, which can be can cancelled with a critical field of ca. 2.0 and 2.5 T at 2 K for compounds 1 and 2, respectively. The magnetic properties of compound 1 have been fit with a simple S = 2 monomer with g = 1.959, a weak zero-field splitting (|D| = 1.23 cm^-1), and a very weak intermolecular interaction (zJ = -0.03 cm^-1). For compound 2, we have used a model with an S = 2 monomer with ZFS plus an S = 2 antiferromagnetically coupled dimer with g = 2.009, |D| = 1.21 cm^-1, and J = -0.42 cm^-1. The metamagnetic behavior of both compounds is attributed to the weak intermolecular π-π and hydrogen-bonding interactions.

Metal-Organic Framework Magnets

Metal-organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal-organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal-organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal-organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal-organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal-organic magnet research that laid the foundation for structurally characterized metal-organic framework magnets. Sections 3 and 4 then outline the literature of metal-organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal-organic framework magnets while maintaining structural integrity and additional function.

Structural diversity and magnetic properties of six cobalt coordination polymers based on 2,2'-phosphinico-dibenzoate ligand

Six novel Co(ii) coordination polymers, namely, [Co₁₀L₆(OH)₂(H₂O)₉]·10.5H₂O (1), [Co₃L₂(3-abpt)₂]·4H₂O (2), [Co₃L₂(4-azpy)₂(H₂O)₂(EtOH)] (3), [Co₃L₂(4,4'-bipy)₂(H₂O)₂(MeCN)] (4), [Co₃L₂(4,4'-bipy)₂] (5), and [Co₅L₂(OH)₂(ina)₂(H₂O)₂] (6) (H₃L = 2,2'-phosphinico-dibenzoic acid, 3-abpt = 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole, 4-azpy = 4,4'-azobispyridine, 4,4'-bipy = 4,4'-bipyridine, Hina = isonicotinic acid), have been hydrothermally synthesized and their magnetic properties have been characterized. The L^3- anion displays six types of coordination modes in the compounds. Compound 1 exhibits a novel 1D ladder-like structure, which consists of non-centrosymmetric Co₁₀ units. Compounds 2-4 comprise 2D networks assembled from Co₃L₂ chains and N-heterocyclic linkers. Compound 5 comprises a 3D framework built from six neighboring parallel Co₃L₂ ladders bridged by 4,4'-bipy linkers. Compound 6 features a 3D framework that exhibits pcu topology with the Schläfli symbol of (4¹²·6³) using a pentanuclear [Co₅(OH)₂]⁸⁺ cluster as the node. Variable-temperature magnetic susceptibility studies indicate that the six coordination polymers exhibit remarkable magnetic behavior such as spin-canted antiferromagnetism and spin glass, which were found to coexist in compound 6.

Selective CO2 Capture and High Proton Conductivity of a Functional Star-of-David Catenane Metal-Organic Framework

Network structures based on Star-of-David catenanes with multiple superior functionalities have been so far elusive, although numerous topologically interesting networks are synthesized. Here, a metal-organic framework featuring fused Star-of-David catenanes is reported. Two triangular metallacycles with opposite handedness are triply intertwined forming a Star-of-David catenane. Each catenane fuses with its six neighbors to generate a porous twofold intercatenated gyroid framework. The compound possesses exceptional stability and exhibits multiple functionalities including highly selective CO₂ capture, high proton conductivity, and coexistence of slow magnetic relaxation and long-range ordering.

Effects of Ru(ii/iii) redox on the Co(ii) coordination number and magnetic properties of 1D cyanide-bridged Co-Ru compounds

A new 1D cyanide-bridged Co-Ru compound, {[trans-Ru^III(dmap)₄(CN)₂Co(dipic)(MeOH)](PF₆)}_n (1a) (dmap = 4-dimethylaminopyridine, dipic = pyridine-2,6-dicarboxylate), and its reduced state, [trans-Ru^II(dmap)₄(CN)₂Co(dipic)]_n (1b) have been synthesized. Upon the Ru center reduction from iii to ii, the MeOH solvent molecule bound to Co(ii) in 1a is expelled. 1a displays ferrimagnetic properties but 1b is only a paramagnetic compound.

Pre-design and synthesis of a five-fold interpenetrated pcu-type porous coordination polymer and its CO2/CO separation

The first five-fold interpenetrated PCP with pcu topology and high porosity was rationally designed and prepared, which showed high separation potential of CO₂/CO mixtures.

Crystal structure of two-dimensional coordination polymer poly-[μ2-azido-aqua-(μ2-pyrazine-2-carboxylato-κ3O,N:N′)nickel(II)], C5H5N5O3Ni

C5H5N5O3Ni, monoclinic, C2/c (no. 15), a = 8.5804(17) Å, b = 13.790(3) Å, c = 13.969(3) Å, β = 104.37(3)°, V =1601.2(6)Å3, Z = 8, Rgt(F) = 0.0203, wRref(F2) = 0.0550, T = 293 K.

Synthesis, structure, magnetic and biological activity studies of bis-hydrazone derived Cu(ii) and Co(ii) coordination compounds

Four coordination compounds of formulae [Cu(II)2(H2L(1))(HL(1))](ClO4)3·H2O (1), [Cu(II)2(H2L(2))(CH3OH)2](ClO4)2·2CH3OH (2), [Co(II)2(H2L(1))2](ClO4)4 (3) and [Co(II)2(H2L(2))2]·2H2O (4) were synthesized via self-assembly of succinohydrazone derived ligands (H2L(1) = N',N'-4-bis(2-pyridyl)succinohydrazide, H4L(2) = N',N'-4-bis(2-hydroxybenzylidene)succinohydrazide) and Cu(2+) and Co(2+) ions, respectively. The compounds were characterized by crystal structure determination, magnetic measurements and biological activities. Compounds 1, 3 and 4 have discrete double helicate structures, whereas compound 2 is a one-dimensional chain. Magnetic studies show antiferromagnetic exchange interactions in 2 with a J value of -67.1 cm(-1) and antiferromagnetic spin-canting in compound 3 originates through supramolecular H-bonding. For compound 3, a clear bifurcation was observed in zero field cooled (ZFC) and field cooled (FC) measurement at a temperature of 3.5 K and field of 0.1 T, implying long range magnetic ordering below this temperature. Interestingly, all of compounds 1-4 show significant changes in their absorption (hypo- and hyperchromism) in the presence of SS-DNA, inferring interaction between the compounds and DNA. In addition, compounds 1-4 significantly exhibited nuclease activities on both RNA and pUC19 plasmid DNA. Moreover, the nuclease activity was further enhanced in the presence of oxidant (H2O2) and suggests the possible role of reactive oxygen species in DNA nicking ability of compounds 1-4. Furthermore, compounds 1, 2 and 4 exhibited significant cytotoxicity against mammalian cancer cell lines (HeLa, A549 and MDAMB-231). In addition, our results from Annexin/PI staining and DNA fragmentation assays revealed that these compounds are capable of inducing apoptosis and have potential to act as anticancer drugs.

An air-stable Dy(iii) single-ion magnet with high anisotropy barrier and blocking temperature

A mononuclear Dy(iii) complex assembled just from five water molecules and two phosphonic diamide ligands combines the advantages of high anisotropy barrier, high blocking temperature and significant coercivity, apart from its remarkable air- and moisture-stability.

Herein we report air-stable Dy(iii) and Er(iii) single-ion magnets (SIMs) with pseudo-D_5h symmetry, synthesized from a sterically encumbered phosphonamide, ^tBuPO(NHⁱPr)₂, where the Dy(iii)-SIM exhibits a magnetization blocking (T_B) up to 12 K, defined from the maxima of the zero-field cooled magnetization curve, with an anisotropy barrier (U_eff) as high as 735.4 K. The Dy(iii)-SIM exhibits a magnetic hysteresis up to 12 K (30 K) with a large coercivity of ∼0.9 T (∼1.5 T) at a sweep rate of ∼0.0018 T s^–1 (0.02 T s^–1). These high values combined with persistent stability under ambient conditions, render this system as one of the best-characterized SIMs. Ab initio calculations have been used to establish the connection between the higher-order symmetry of the molecule and the quenching of quantum tunnelling of magnetization (QTM) effects. The relaxation of magnetization is observed via the second excited Kramers doublet owing to pseudo-high-order symmetry, which quenches the QTM. This study highlights fine-tuning of symmetry around the lanthanide ion to obtain new-generation SIMs and offers further scope for pushing the limits of U_eff and T_B using this approach.

ZnII and CdII MOFs based on an amidoisophthalic acid ligand: synthesis, structure and catalytic application in transesterification

Metal–organic frameworks of Zn(ii) and Cd(ii) act as recyclable heterogeneous catalysts for the transesterification reaction of carboxylate esters.

Three Chiral Schiff-Base-Manganese(III)-Based Complexes: Synthesis, Structures and Magnetic Properties

Three chiral manganese(III) Schiff-base complexes [Mn(R,R-Salcy)(CH3OH)(N3)], [Mn(S,S-Salcy)(DMF)(N3)] (both monomers by X-structure determination) and the trinuclear complex (X-ray structure) {[Mn(R,R-Salcy)(H2O)]2[μ-Ni(CN)4]}·3CH3OH·H2O [Salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato)dianion)] have been synthesised. The trimeric complex shows weak antiferromagnetic interactions between the adjacent Mn(III) ions.

Spontaneous Magnetization in Homometallic μ6-Oxalate Coordination Polymers

The reaction of 1,2,4-triazole and NaF with M(ox) (M = transition-metal dication; ox = oxalate dianion) under hydrothermal conditions has led to the isolation of a variety of hybrid organic-inorganic coordination polymers. Four structurally different 3D networks were obtained, depending on the transition metal, with stoichiometry [M2(H2O)(μ2-ox)][M2(μ3-trz)6] [M = Fe (1), Co (2), Ni (3)], [Zn2(H2O)(μ3-trz)2(μ2-ox)] (4), [Mn3(μ3-trz)2(μ6-ox)(μ3-F)2] (5), and [Fe3(μ3-trz)2(μ6-ox)(μ2-F)2] (6). In all cases, the magnetic behavior is dominated by antiferromagnetic exchange interactions between paramagnetic centers. Remarkably, 5 and 6 present a novel magnetic connectivity around the oxalate anion: a μ6-bridging mode. This magnetic geometry promotes multiple triangular arrangements among antiferromagnetically coupled spin carriers, resulting in a complex magnetic network because of the presence of competing interactions. These materials exhibit spontaneous magnetization below 9 and 66 K, respectively.

Synthesis, characterization and magnetism of metal–organic compounds: role of the positions of the coordinating groups of a meso-flexible ligand in placing anisotropy to exhibit spin-canting behaviour

Magnetic anisotropy can be included in metal–organic coordination polymers by altering the position of the coordinating groups on the skeleton of the ligand.

Solvent-controlled structural diversity observed in three Cu(ii) MOFs with a 2,2′-dinitro-biphenyl-4,4′-dicarboxylate ligand: synthesis, structures and magnetism

Three solvent-dependent 3D Cu^II-based MOFs with diverse topology net have been successfully separated under controllable solvothermal conditions and magnetic studies suggest homo-spin topological ferrimagnetic and antiferromagnetic interactions.

Field-induced dynamic magnetic behaviour of a canted weak ferromagnetic chain material

A 1-D [Mn^III₃O] based magnetic chain material amazingly exhibits the coexistence of spin-glass, spin-canting, and metamagnetic behaviours as well as slow relaxation of magnetization under different applied magnetic fields.

The concept of mixed organic ligands in metal–organic frameworks: design, tuning and functions

The mixed organic ligand strategy is significant for the rational construction of MOFs, and furthermore for their functionality and tunability.

An unusual magnetic response in a π-stacked 66-dia net structure of [4 + 2] copper(ii) cubane

Unusual hysteresis loops with coercivity maximum (∼2000 Oe) at 20 K are observed in a copper(ii) cubane. The apparent anomaly appears due to variation of intercubane π⋯π stacking with thermal energy.