Combination of Magnetic Susceptibility and Electron Paramagnetic Resonance to Monitor the 1D to 2D Solid State Transformation in Flexible Metal–Organic Frameworks of Co(II) and Zn(II) with 1,4-Bis(triazol-1-ylmethyl)benzene

Two families of coordination polymers, {[M­(btix)₂(OH₂)₂]·2NO₃·2H₂O}_<i>n</i> [M = Co (<b>1</b>), Zn (<b>2</b>), Co–Zn (<b>3</b>); btix = 1,4-bis­(triazol-1-ylmethyl)­benzene] and {[M­(btix)₂(NO₃)₂]}_<i>n</i> [M = Co (<b>4</b>), Zn (<b>5</b>), Co–Zn (<b>6</b>)], have been synthesized and characterized. The two conformations of the ligand, <i>syn</i> and <i>anti</i>, lead to one-dimensional (1D) cationic chains or two-dimensional (2D) neutral grids. Extrusion of the water molecules of the 1D compounds results in an irreversible transformation into the 2D compounds, which involves a change in conformation of the btix ligands and a rearrangement in the metal environment with cleavage and reformation of covalent bonds. This structural transformation has been followed by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements to monitor the minor modifications that the metal centers suffer

Combination of Magnetic Susceptibility and Electron Paramagnetic Resonance to Monitor the 1D to 2D Solid State Transformation in Flexible Metal–Organic Frameworks of Co(II) and Zn(II) with 1,4-Bis(triazol-1-ylmethyl)benzene

Two families of coordination polymers, {[M­(btix)₂(OH₂)₂]·2NO₃·2H₂O}_<i>n</i> [M = Co (<b>1</b>), Zn (<b>2</b>), Co–Zn (<b>3</b>); btix = 1,4-bis­(triazol-1-ylmethyl)­benzene] and {[M­(btix)₂(NO₃)₂]}_<i>n</i> [M = Co (<b>4</b>), Zn (<b>5</b>), Co–Zn (<b>6</b>)], have been synthesized and characterized. The two conformations of the ligand, <i>syn</i> and <i>anti</i>, lead to one-dimensional (1D) cationic chains or two-dimensional (2D) neutral grids. Extrusion of the water molecules of the 1D compounds results in an irreversible transformation into the 2D compounds, which involves a change in conformation of the btix ligands and a rearrangement in the metal environment with cleavage and reformation of covalent bonds. This structural transformation has been followed by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements to monitor the minor modifications that the metal centers suffer

Solvent-Free Synthesis of a Pillared Three-Dimensional Coordination Polymer with Magnetic Ordering

A new magnetic coordination polymer, [Fe­(bipy)­(im)₂] (bipy = 4,4-bipyridine and im = imidazole), has been synthesized in a solvent-free reaction. Structural analysis reveals a pillared 3D coordination polymer composed by neutral layers, formed by iron­(II) and imidazolate linkers, interconnected by bipy ligands which serve as pillars. Magnetic measurements show that the material magnetically orders at low temperatures (<i>T</i>_c = 14.5 K) as a weak ferromagnet, likely due to a spin canting

A Mixed-Ligand Approach for Spin-Crossover Modulation in a Linear Fe^II Coordination Polymer

In this work, we present a family of Fe^II coordination polymers of general formula [Fe­(btzx)_{3–3<i>x</i>}(btix)_3<i>x</i>]­(ClO₄)₂ with interesting spin-crossover properties. These coordination polymers have been synthesized using chemical mixtures of two different but closely related ligands, 1,4-bis­(tetrazol-1-ylmethyl)­benzene (btzx) and 1,4-bis­(triazol-1-ylmethyl)­benzene (btix), and the effect of a gradual substitution of the ligand in the spin transition temperature has been investigated. Several chemical mixtures have been structurally characterized by X-ray powder diffraction indicating a clear critical amount in the composition of the mixture after which mixed phases rather than a single phase comprising mixed components are observed. Importantly, this approach causes the appearance of a new transition at lower temperatures that is not present in the pure [Fe­(L)₃]­(ClO₄)₂ systems

Dynamic Magnetic Materials Based on the Cationic Coordination Polymer [Cu(btix)₂]_<i>n</i>^2<i>n</i>+ [btix = 1,4-Bis(triazol-1-ylmethyl)benzene]: Tuning the Structural and Magnetic Properties through Anion Exchange

A three-dimensional coordination polymer, [Cu­(btix)₂(BF₄)₂]_<i>n</i> [btix = 1,4-bis­(triazol-1-ylmethyl)­benzene], with antiferromagnetic interactions occurring via the organic ligand, has been prepared and characterized. It has been shown to permit the exchange of anionic species in the crystalline network with modification of the magnetic properties. Coordinated BF₄^– can be reversibly exchanged by different anions with (NO₃^– and Cl^–) or without (PF₆^– and ClO₄^–) dynamic response of the organic ligand, which acts as the only linker between the metal centers. Interestingly, an irreversible exchange occurs with N₃^– anions to generate a new coordination polymer, [Cu­(btix)­(N₃)₂]_<i>n</i>, whose structure has been determined ab initio by powder X-ray diffraction, revealing a totally different connectivity between the Cu^II centers. These structural transformations are accompanied by a change of the magnetic properties, which have been detected by electron paramagnetic resonance and magnetic susceptibility measurements

Spin-Crossover Modification through Selective CO₂ Sorption

We present a spin-crossover Fe^II coordination polymer with no permanent channels that selectively sorbs CO₂ over N₂. The one-dimensional chains display internal voids of ∼9 Å diameter, each being capable to accept one molecule of CO₂ at 1 bar and 273 K. X-ray diffraction provides direct structural evidence of the location of the gas molecules and reveals the formation of OCO­(δ^–)···π interactions. This physisorption modifies the spin transition, producing a 9 K increase in <i>T</i>_1/2

Spin-Crossover Modification through Selective CO₂ Sorption

We present a spin-crossover Fe^II coordination polymer with no permanent channels that selectively sorbs CO₂ over N₂. The one-dimensional chains display internal voids of ∼9 Å diameter, each being capable to accept one molecule of CO₂ at 1 bar and 273 K. X-ray diffraction provides direct structural evidence of the location of the gas molecules and reveals the formation of OCO­(δ^–)···π interactions. This physisorption modifies the spin transition, producing a 9 K increase in <i>T</i>_1/2

Spin-Crossover Modification through Selective CO₂ Sorption

We present a spin-crossover Fe^II coordination polymer with no permanent channels that selectively sorbs CO₂ over N₂. The one-dimensional chains display internal voids of ∼9 Å diameter, each being capable to accept one molecule of CO₂ at 1 bar and 273 K. X-ray diffraction provides direct structural evidence of the location of the gas molecules and reveals the formation of OCO­(δ^–)···π interactions. This physisorption modifies the spin transition, producing a 9 K increase in <i>T</i>_1/2

Hybrid Magnetic Superconductors Formed by TaS₂ Layers and Spin Crossover Complexes

The restacking of charged TaS₂ nanosheets with molecular counterparts has so far allowed for the combination of superconductivity with a manifold of other molecule-intrinsic properties. Yet, a hybrid compound that blends superconductivity with spin crossover switching has still not been reported. Here we continue to exploit the solid-state/molecule-based hybrid approach for the synthesis of a layered TaS₂-based material that hosts Fe²⁺ complexes with a spin switching behavior. The chemical design and synthetic aspects of the exfoliation/restacking approach are discussed, highlighting how the material can be conveniently obtained in the form of highly oriented easy-to-handle flakes. Finally, proof of the presence of both phenomena is provided by the use of a variety of physical characterization techniques. The likely sensitivity of the intercalated Fe²⁺ complexes to external stimuli such as light opens the door for the study of synergistic effects between the superconductivity and the spin crossover switching at low temperatures