Novel Iron(II) Microporous Spin-Crossover Coordination Polymers with Enhanced Pore Size

In this Communication, we report the synthesis and characterization of novel Hofmann-like spin-crossover porous coordination polymers of composition {Fe­(L)­[M­(CN)₄]}·G [L = 1,4-bis­(4-pyridylethynyl)­benzene and M^II = Ni, Pd, and Pt]. The spin-crossover properties of the framework are closely related to the number and nature of the guest molecules included in the pores

Novel Iron(II) Microporous Spin-Crossover Coordination Polymers with Enhanced Pore Size

In this Communication, we report the synthesis and characterization of novel Hofmann-like spin-crossover porous coordination polymers of composition {Fe­(L)­[M­(CN)₄]}·G [L = 1,4-bis­(4-pyridylethynyl)­benzene and M^II = Ni, Pd, and Pt]. The spin-crossover properties of the framework are closely related to the number and nature of the guest molecules included in the pores

Synthesis of Nanocrystals and Particle Size Effects Studies on the Thermally Induced Spin Transition of the Model Spin Crossover Compound [Fe(phen)₂(NCS)₂]

Surfactant-free nanocrystals of the model spin-crossover compound [Fe­(phen)₂(NCS)₂] (phen: 1,10-phenanthroline) have been synthesized applying the reverse micelle technique. The morphology of the nanocrystals, characterized by scanning electronic microscopy, corresponds to rhombohedric platelets with dimensions ranging from 203 × 203 × 106 nm to 142 × 142 × 74 nm. Variation of the concentration of the Fe­(BF₄)₂·6H₂O salt in the synthesis has been found to have little influence on the crystallite size. In contrast, the solvent–surfactant ratio (ω) is critical for a good particle growth. The spin transition of the nanocrystals has been characterized by magnetic susceptibility measurements and Mössbauer spectroscopy. The nanocrystals undergo an abrupt and more cooperative spin transition in comparison with the bulk compound. The spin transition is centered in the interval of temperature of 175–185 K and is accompanied by 8 K of thermal hysteresis width. The crystallite quality more than the crystallite size is responsible for the higher cooperativity. The magnetic properties of the nanocrystals embedded in organic polymers such as polyethylene glycol, nujol, glycerol, and triton have been studied as well. The spin transition in the nanocrystals is affected by the polymer coating. The abrupt and first-order spin transition transforms into a more continuous spin transition as a result of the chemical pressure asserted by the organic polymers on the Fe­(II) centers

Fast Detection of Water and Organic Molecules by a Change of Color in an Iron(II) Microporous Spin-Crossover Coordination Polymer

Here we present a novel three-dimensional iron­(II) spin-crossover porous coordination polymer based on the bis­(1,2,4-triazol-4-yl)­adamantane (tr₂ad) ligand and the [Au­(CN)₂]⁻ metalloligand anions with the formula {Fe₃(tr₂ad)₄[Au­(CN)₂)]₂}­[Au­(CN)₂]₄·G. The sorption/desorption of guest molecules, water, and five/six-membered-ring organic molecules is easily detectable because the guest-free and -loaded frameworks present drastically distinct coloration and spin-state configurations

Fast Detection of Water and Organic Molecules by a Change of Color in an Iron(II) Microporous Spin-Crossover Coordination Polymer

Here we present a novel three-dimensional iron­(II) spin-crossover porous coordination polymer based on the bis­(1,2,4-triazol-4-yl)­adamantane (tr₂ad) ligand and the [Au­(CN)₂]⁻ metalloligand anions with the formula {Fe₃(tr₂ad)₄[Au­(CN)₂)]₂}­[Au­(CN)₂]₄·G. The sorption/desorption of guest molecules, water, and five/six-membered-ring organic molecules is easily detectable because the guest-free and -loaded frameworks present drastically distinct coloration and spin-state configurations

Heterobimetallic MOFs Containing Tetrathiocyanometallate Building Blocks: Pressure-Induced Spin Crossover in the Porous {Fe^II(pz)[Pd^II(SCN)₄]} 3D Coordination Polymer

Here we describe the synthesis, structure, and magnetic properties of two related coordination polymers made up of self-assembling Fe­(II) ions, pyrazine (pz), and the tetrathiocyanopalladate anion. Compound {Fe­(MeOH)₂[Pd­(SCN)₄]}·pz (<b>1a</b>) is a two-dimensional coordination polymer where the Fe­(II) ions are equatorially coordinated by the nitrogen atoms of four [Pd­(SCN)₄]^2– anions, each of which connects four Fe­(II) ions, forming corrugated layers {Fe­[Pd­(SCN)₄]}_∞. The coordination sphere of Fe­(II) is completed by the oxygen atoms of two CH₃OH molecules. The layers stack one on top of each other in such a way that the included pz molecule establishes strong hydrogen bonds with the coordinated methanol molecules of adjacent layers. Compound {Fe­(pz)­[Pd­(SCN)₄]} (<b>2</b>) is a three-dimensional porous coordination polymer formed by flat {Fe­[Pd­(SCN)₄]}_∞ layers pillared by the pz ligand. Thermal analysis of <b>1a</b> shows a clear desorption of the two coordinated CH₃OH molecules giving a rather stable phase (<b>1b</b>), which presumably is a polymorphic form of <b>2</b>. The magnetic properties of the three derivatives are typical of the high-spin Fe­(II) compounds. However, compounds <b>1b</b> and <b>2</b>, with coordination sphere [FeN₆], show thermal spin crossover behavior at pressures higher than ambient pressure (10⁵ MPa)

Heterobimetallic MOFs Containing Tetrathiocyanometallate Building Blocks: Pressure-Induced Spin Crossover in the Porous {Fe^II(pz)[Pd^II(SCN)₄]} 3D Coordination Polymer

Here we describe the synthesis, structure, and magnetic properties of two related coordination polymers made up of self-assembling Fe­(II) ions, pyrazine (pz), and the tetrathiocyanopalladate anion. Compound {Fe­(MeOH)₂[Pd­(SCN)₄]}·pz (<b>1a</b>) is a two-dimensional coordination polymer where the Fe­(II) ions are equatorially coordinated by the nitrogen atoms of four [Pd­(SCN)₄]^2– anions, each of which connects four Fe­(II) ions, forming corrugated layers {Fe­[Pd­(SCN)₄]}_∞. The coordination sphere of Fe­(II) is completed by the oxygen atoms of two CH₃OH molecules. The layers stack one on top of each other in such a way that the included pz molecule establishes strong hydrogen bonds with the coordinated methanol molecules of adjacent layers. Compound {Fe­(pz)­[Pd­(SCN)₄]} (<b>2</b>) is a three-dimensional porous coordination polymer formed by flat {Fe­[Pd­(SCN)₄]}_∞ layers pillared by the pz ligand. Thermal analysis of <b>1a</b> shows a clear desorption of the two coordinated CH₃OH molecules giving a rather stable phase (<b>1b</b>), which presumably is a polymorphic form of <b>2</b>. The magnetic properties of the three derivatives are typical of the high-spin Fe­(II) compounds. However, compounds <b>1b</b> and <b>2</b>, with coordination sphere [FeN₆], show thermal spin crossover behavior at pressures higher than ambient pressure (10⁵ MPa)

Heterobimetallic MOFs Containing Tetrathiocyanometallate Building Blocks: Pressure-Induced Spin Crossover in the Porous {Fe^II(pz)[Pd^II(SCN)₄]} 3D Coordination Polymer

Here we describe the synthesis, structure, and magnetic properties of two related coordination polymers made up of self-assembling Fe­(II) ions, pyrazine (pz), and the tetrathiocyanopalladate anion. Compound {Fe­(MeOH)₂[Pd­(SCN)₄]}·pz (<b>1a</b>) is a two-dimensional coordination polymer where the Fe­(II) ions are equatorially coordinated by the nitrogen atoms of four [Pd­(SCN)₄]^2– anions, each of which connects four Fe­(II) ions, forming corrugated layers {Fe­[Pd­(SCN)₄]}_∞. The coordination sphere of Fe­(II) is completed by the oxygen atoms of two CH₃OH molecules. The layers stack one on top of each other in such a way that the included pz molecule establishes strong hydrogen bonds with the coordinated methanol molecules of adjacent layers. Compound {Fe­(pz)­[Pd­(SCN)₄]} (<b>2</b>) is a three-dimensional porous coordination polymer formed by flat {Fe­[Pd­(SCN)₄]}_∞ layers pillared by the pz ligand. Thermal analysis of <b>1a</b> shows a clear desorption of the two coordinated CH₃OH molecules giving a rather stable phase (<b>1b</b>), which presumably is a polymorphic form of <b>2</b>. The magnetic properties of the three derivatives are typical of the high-spin Fe­(II) compounds. However, compounds <b>1b</b> and <b>2</b>, with coordination sphere [FeN₆], show thermal spin crossover behavior at pressures higher than ambient pressure (10⁵ MPa)

Reversible Chemisorption of Sulfur Dioxide in a Spin Crossover Porous Coordination Polymer

The chemisorption of sulfur dioxide (SO₂) on the Hofmann-like spin crossover porous coordination polymer (SCO-PCP) {Fe­(pz)­[Pt­(CN)₄]} has been investigated at room temperature. Thermal analysis and adsorption–desorption isotherms showed that ca. 1 mol of SO₂ per mol of {Fe­(pz)­[Pt­(CN)₄]} was retained in the pores. Nevertheless, the SO₂ was loosely attached to the walls of the host network and completely released in 24 h at 298 K. Single crystals of {Fe­(pz)­[Pt­(CN)₄]}·<i>n</i>SO₂ (<i>n</i> ≈ 0.25) were grown in water solutions saturated with SO₂, and its crystal structure was analyzed at 120 K. The SO₂ molecule is coordinated to the Pt^II ion through the sulfur atom ion, Pt–S = 2.585(4) Å. This coordination slightly stabilizes the low-spin state of the Fe^II ions shifting the critical temperatures of the spin transition by 8–12 K. DFT calculations have been performed to rationalize these observations