Gadolinium Sulfate Modified by Formate To Obtain Optimized Magneto-Caloric Effect

Three new Gd^III based coordination polymers [Gd₂(C₂H₆SO)­(SO₄)₃(H₂O)₂]<i>_n</i> (<b>1</b>), {[Gd₄­(HCOO)₂­(SO₄)₅­(H₂O)₆]·H₂O}<i>_n</i> (<b>2</b>), and [Gd­(HCOO)­(SO₄)­(H₂O)]<i>_n</i> (<b>3</b>) were obtained by modifying gadolinium sulfate. With the gradual increase of the volume ratio of HCOOH and DMSO in synthesis, the formate anions begin to coordinate with metal centers; this results in the coordination numbers of sulfate anion increasing and the contents of water and DMSO molecules decreasing in target complexes. Accordingly, spin densities both per mass and per volume were enhanced step by step, which are beneficial for the magneto-caloric effect (MCE). Magnetic studies reveal that with the more formate anions present, the larger the negative value of magnetic entropy change (−Δ<i>S</i>_m) is. Complex <b>3</b> exhibits the largest −Δ<i>S</i>_m = 49.91 J kg^–1 K^–1 (189.51 mJ cm^–3 K^–1) for <i>T</i> = 2 K and Δ<i>H</i> = 7 T among three new complexes

Tuning the Structure and Magnetism of Heterometallic Sodium(1+)–Cobalt(2+) Formate Coordination Polymers by Varying the Metal Ratio and Solvents

Three new heterometallic formate coordination polymers formulated as [Na₂Co­(HCOO)₄]_∞ (<b>1</b>), [NaCo­(HCOO)₃]_∞ (<b>2</b>), and [Na₂Co₇(HCOO)₁₆]_∞ (<b>3</b>) were obtained by adjusting the solvent and ratio of the reactants. In <b>1</b>, a (4,4) cobalt formate layer is formed and the sodium ions connect the layers to form a three-dimensional (3D) framework. In <b>2</b>, each formate ligand binds two Co²⁺ and two Na⁺ ions with a syn,syn,anti,anti coordination mode to form a chrial network with 4,6-connected topology. <b>3</b> is a Na⁺-ion-linked 3D framework based on the cobalt formate layer, which has a 10-membered metal ring. Magnetic studies indicate the existence of ferromagnetic interactions between adjacent Co²⁺ ions in <b>1</b>, while dominating antiferromagnetic couplings in <b>2</b> and <b>3</b>

Tuning the Subunits and Topologies in Cluster-Based Cobalt–Organic Frameworks by Varying the Reaction Conditions

Different ways of anions introduction were applied to construct cluster-based frameworks, owning to the versatile coordination ability of the formate anion and its sensitivity to the pH value of the reaction system. Three tetra-, penta-, and hexanuclear cluster-based cobalt-organic frameworks, [Co₂(<b>L</b>)₃(HCO₂)·MeOH]_<i>n</i> (<b>1</b>), [Co₅(<b>L</b>)₆(OH)₂(NO₃)₂·2H₂O]_<i>n</i> (<b>2</b>), and [Co<b>L</b>(HCO₂)]_<i>n</i> (<b>3</b>) [<b>L</b> = (<i>E</i>)-3-(pyridin-3-yl)­acrylate], have been successfully synthesized. In these complexes, each Co^II cluster is linked by twelve <b>L</b> ligands with different connectivities to generate unique topological nets. In <b>1</b>, two formate anions link four Co^II ions forming a tetranuclear cluster, and each of the tetranuclear clusters is connected to eight neighbors by <b>L</b> ligands, giving an 8-connected 3⁶4¹⁸5³6 net. In <b>2</b>, the pentanuclear cluster is formed by five Co^II ions linked through two OH^– and six carboxylate groups, which are further connected by <b>L</b> ligands to afford a <i>pcu</i> (primitive cubic lattice) net. Different from <b>1</b> and <b>2</b>, complex <b>3</b> is a 2-fold interpenetrating <i>pcu</i> net based on hexanuclear clusters, which are formed by the linkage of six Co^II ions with six syn,syn,anti formate anions and six syn syn carboxylate groups. Magnetic studies indicated that domain antiferromagnetic interactions exist between Co^II ions, and spin competition exists in <b>2</b> and <b>3</b>

Tuning the Subunits and Topologies in Cluster-Based Cobalt–Organic Frameworks by Varying the Reaction Conditions

Different ways of anions introduction were applied to construct cluster-based frameworks, owning to the versatile coordination ability of the formate anion and its sensitivity to the pH value of the reaction system. Three tetra-, penta-, and hexanuclear cluster-based cobalt-organic frameworks, [Co₂(<b>L</b>)₃(HCO₂)·MeOH]_<i>n</i> (<b>1</b>), [Co₅(<b>L</b>)₆(OH)₂(NO₃)₂·2H₂O]_<i>n</i> (<b>2</b>), and [Co<b>L</b>(HCO₂)]_<i>n</i> (<b>3</b>) [<b>L</b> = (<i>E</i>)-3-(pyridin-3-yl)­acrylate], have been successfully synthesized. In these complexes, each Co^II cluster is linked by twelve <b>L</b> ligands with different connectivities to generate unique topological nets. In <b>1</b>, two formate anions link four Co^II ions forming a tetranuclear cluster, and each of the tetranuclear clusters is connected to eight neighbors by <b>L</b> ligands, giving an 8-connected 3⁶4¹⁸5³6 net. In <b>2</b>, the pentanuclear cluster is formed by five Co^II ions linked through two OH^– and six carboxylate groups, which are further connected by <b>L</b> ligands to afford a <i>pcu</i> (primitive cubic lattice) net. Different from <b>1</b> and <b>2</b>, complex <b>3</b> is a 2-fold interpenetrating <i>pcu</i> net based on hexanuclear clusters, which are formed by the linkage of six Co^II ions with six syn,syn,anti formate anions and six syn syn carboxylate groups. Magnetic studies indicated that domain antiferromagnetic interactions exist between Co^II ions, and spin competition exists in <b>2</b> and <b>3</b>

Azido-Directed Formation of An Unprecedented Mn(II)-Organic Framework with Nanoscale Cubic Cage Units

A <i>bcu</i> topological three-dimensional Mn­(II)-organic framework [Mn₂₂(N₃)₈(L)₁₂(H₂O)₂₆·5H₂O]_∞ (<b>1</b>) <i></i>(L = 1,2,3-triazole-4,5-dicarboxylate) based on an unprecedented nanoscale cage has been hydrothermally synthesized. Dominating antiferromagnetic interactions were detected between the Mn^II ions in <b>1</b>

Tuning the Subunits and Topologies in Cluster-Based Cobalt–Organic Frameworks by Varying the Reaction Conditions

Different ways of anions introduction were applied to construct cluster-based frameworks, owning to the versatile coordination ability of the formate anion and its sensitivity to the pH value of the reaction system. Three tetra-, penta-, and hexanuclear cluster-based cobalt-organic frameworks, [Co₂(<b>L</b>)₃(HCO₂)·MeOH]_<i>n</i> (<b>1</b>), [Co₅(<b>L</b>)₆(OH)₂(NO₃)₂·2H₂O]_<i>n</i> (<b>2</b>), and [Co<b>L</b>(HCO₂)]_<i>n</i> (<b>3</b>) [<b>L</b> = (<i>E</i>)-3-(pyridin-3-yl)­acrylate], have been successfully synthesized. In these complexes, each Co^II cluster is linked by twelve <b>L</b> ligands with different connectivities to generate unique topological nets. In <b>1</b>, two formate anions link four Co^II ions forming a tetranuclear cluster, and each of the tetranuclear clusters is connected to eight neighbors by <b>L</b> ligands, giving an 8-connected 3⁶4¹⁸5³6 net. In <b>2</b>, the pentanuclear cluster is formed by five Co^II ions linked through two OH^– and six carboxylate groups, which are further connected by <b>L</b> ligands to afford a <i>pcu</i> (primitive cubic lattice) net. Different from <b>1</b> and <b>2</b>, complex <b>3</b> is a 2-fold interpenetrating <i>pcu</i> net based on hexanuclear clusters, which are formed by the linkage of six Co^II ions with six syn,syn,anti formate anions and six syn syn carboxylate groups. Magnetic studies indicated that domain antiferromagnetic interactions exist between Co^II ions, and spin competition exists in <b>2</b> and <b>3</b>

The Design of Dual-Emissive Composite Material [Zn₂(HL)₃]⁺@MOF‑5 as Self-Calibrating Luminescent Sensors of Al³⁺ Ions and Monoethanolamine

Introducing another chromophore into a luminescent MOF is a potential way to assembling novel dual-emissive luminescent materials. Putting the chromophore, for which luminescence can be enhanced by Zn²⁺ ion, into MOF-5 by the “bottle around ship” strategy is a simple but efficient synthesis method to realize such dual-emissive materials. According to this strategy, a novel dual-emissive luminescent composite material [Zn₂(HL)₃]⁺@MOF-5 was constructed by loading the [La₃(HL)₂L₂(NO₃)₃H₂O] (<b>1</b>) (H₂L = 7,7′-(ethane-1,1′-diyl)­8-hydro-quinoline) into MOF-5, in which the [Zn₂(HL)₃]⁺ anions were transformed from <b>1</b> with the existence of Zn²⁺. The dual-emissive composite materials show excellent luminescence with two emissions of MOF-5 at 410 nm and [Zn₂(HL)₃]⁺ at 524 nm. Furthermore, by combining characteristics of MOF-5 and the guest chromophore, the composite material is highly selectively sensitive toward Al³⁺ and monoethanolamine, which makes [Zn₂(HL)₃]⁺@MOF-5 a potential self-calibrated fluorescence sensor

A High Working Temperature Multiferroic Induced by Inverse Temperature Symmetry Breaking

Molecular-based multiferroic materials that possess ferroelectric and ferroelastic orders simultaneously have attracted tremendous attention for their potential applications in multiple-state memory devices, molecular switches, and information storage systems. However, it is still a great challenge to effectively construct novel molecular-based multiferroic materials with multifunctionalities. Generally, the structure of these materials possess high symmetry at high temperatures, while processing an obvious order–disorder or displacement-type ferroelastic or ferroelectric phase transition triggered by symmetry breaking during the cooling processes. Therefore, these materials can only function below the Curie temperature (Tc), the low of which is a severe impediment to their practical application. Despite great efforts to elevate Tc, designing single-phase crystalline materials that exhibit multiferroic orders above room temperature remains a challenge. Here, an inverse temperature symmetry-breaking phenomenon was achieved in [FPM][Fe3(μ3-O)(μ-O2CH)8] (FPM stands for 3-(3-formylamino-propyl)-3,4,5,6-tetrahydropyrimidin-1-ium, which acts as the counterions and the rotor component in the network), enabling a ferroelastoelectric phase at a temperature higher than Tc (365 K). Upon heating from room temperature, two-step distinct symmetry breaking with the mm2Fm species leads to the coexistence of ferroelasticity and ferroelectricity in the temperature interval of 365–426 K. In the first step, the FPM cations undergo a conformational flip-induced inverse temperature symmetry breaking; in the second step, a typical ordered–disordered motion-induced symmetry breaking phase transition can be observed, and the abnormal inverse temperature symmetry breaking is unprecedented. Except for the multistep ferroelectric and ferroelastic switching, this complex also exhibits fascinating nonlinear optical switching properties. These discoveries not only signify an important step in designing novel molecular-based multiferroic materials with high working temperatures, but also inspire their multifunctional applications such as multistep switches

A High Working Temperature Multiferroic Induced by Inverse Temperature Symmetry Breaking

Molecular-based multiferroic materials that possess ferroelectric and ferroelastic orders simultaneously have attracted tremendous attention for their potential applications in multiple-state memory devices, molecular switches, and information storage systems. However, it is still a great challenge to effectively construct novel molecular-based multiferroic materials with multifunctionalities. Generally, the structure of these materials possess high symmetry at high temperatures, while processing an obvious order–disorder or displacement-type ferroelastic or ferroelectric phase transition triggered by symmetry breaking during the cooling processes. Therefore, these materials can only function below the Curie temperature (Tc), the low of which is a severe impediment to their practical application. Despite great efforts to elevate Tc, designing single-phase crystalline materials that exhibit multiferroic orders above room temperature remains a challenge. Here, an inverse temperature symmetry-breaking phenomenon was achieved in [FPM][Fe3(μ3-O)(μ-O2CH)8] (FPM stands for 3-(3-formylamino-propyl)-3,4,5,6-tetrahydropyrimidin-1-ium, which acts as the counterions and the rotor component in the network), enabling a ferroelastoelectric phase at a temperature higher than Tc (365 K). Upon heating from room temperature, two-step distinct symmetry breaking with the mm2Fm species leads to the coexistence of ferroelasticity and ferroelectricity in the temperature interval of 365–426 K. In the first step, the FPM cations undergo a conformational flip-induced inverse temperature symmetry breaking; in the second step, a typical ordered–disordered motion-induced symmetry breaking phase transition can be observed, and the abnormal inverse temperature symmetry breaking is unprecedented. Except for the multistep ferroelectric and ferroelastic switching, this complex also exhibits fascinating nonlinear optical switching properties. These discoveries not only signify an important step in designing novel molecular-based multiferroic materials with high working temperatures, but also inspire their multifunctional applications such as multistep switches

Design and Synthesis of Stable Cobalt-Based Weak Ferromagnetic Framework with Large Spin Canting Angle

It still remains a great challenge to design and construct framework-structured weak ferromagnets with large canting angle which is an effective approach for high performance magnets. According to the strategy of antisymmetric interaction causing spin canting, we report the design of four cobalt compounds, which were tested by X-ray single crystal diffraction, TGA, PXRD, and magnetic measurement. Single-crystal structure analysis reveals that compound <b>1</b> has a 2D structure, complex <b>2</b> has a 3,4-connected 3D framework, and complex <b>3</b> exhibits a 3D net structure with rare 3,5-connected 2-nodal β-SnF₂ topology and the solvent MeOH trapped in the 3D channels as guests. The magnetic property of <b>3</b> is spin canting just as designed, with <i>T</i>_N about 4.0 K and large canting angle of 14.8°. Highly stable compound <b>3</b> sustains its framework in air for more than 12 months, in which the guest MeOH molecules can be replaced by water to form complex <b>4</b>