Pulsed-Laser Switching in the Bistability Domain of a Cooperative Spin Crossover Compound: A Critical Study through Calorimetry

The photoswitching from the low spin (LS) to high spin (HS) state and the reverse process in the bistability domain of spin crossover (SCO) compounds is a promising function to be used in molecular electronic devices, and evidenced mainly through spectroscopy. The phenomenon, and in particular its mechanism, is however still under debate since some controversial experimental results have been reported. Here we present a calorimetric experimental study of the photoswitching of the [Fe­(pyrazine)­Pt­(CN)₄] SCO material by a nanosecond-pulsed green laser. Our results confirm that the single laser pulse of varying energies results in significant LS to HS transformations and show that calorimetry provides an accurate quantification of the overall conversion. Successive pulses allow increasing the conversion, achieving a maximum of 60% under our experimental conditions. The HS to LS transformation is on the other hand not induced at any laser fluences contrary to previous reports. The results are compared with those reported with Raman spectroscopy and critically discussed in terms of efficiency of the transformation and potential thermal effects

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)

The Role of Order–Disorder Transitions in the Quest for Molecular Multiferroics: Structural and Magnetic Neutron Studies of a Mixed Valence Iron(II)–Iron(III) Formate Framework

Neutron diffraction studies have been carried out to shed light on the unprecedented order–disorder phase transition (ca. 155 K) observed in the mixed-valence iron­(II)–iron­(III) formate framework compound [NH₂(CH₃)₂]_<i>n</i>[Fe^IIIFe^II(HCOO)₆]_<i>n</i>. The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order–disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe^IIIFe^II(HCOO)₆]_<i>n</i> framework. In the low-temperature phase, a change in space group from <i>P</i>3̅1<i>c</i> to <i>R</i>3̅<i>c</i> occurs, involving a tripling of the <i>c</i>-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe^II and Fe^III magnetic moments

The Role of Order–Disorder Transitions in the Quest for Molecular Multiferroics: Structural and Magnetic Neutron Studies of a Mixed Valence Iron(II)–Iron(III) Formate Framework

Neutron diffraction studies have been carried out to shed light on the unprecedented order–disorder phase transition (ca. 155 K) observed in the mixed-valence iron­(II)–iron­(III) formate framework compound [NH₂(CH₃)₂]_<i>n</i>[Fe^IIIFe^II(HCOO)₆]_<i>n</i>. The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order–disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe^IIIFe^II(HCOO)₆]_<i>n</i> framework. In the low-temperature phase, a change in space group from <i>P</i>3̅1<i>c</i> to <i>R</i>3̅<i>c</i> occurs, involving a tripling of the <i>c</i>-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe^II and Fe^III magnetic moments

The Role of Order–Disorder Transitions in the Quest for Molecular Multiferroics: Structural and Magnetic Neutron Studies of a Mixed Valence Iron(II)–Iron(III) Formate Framework

Neutron diffraction studies have been carried out to shed light on the unprecedented order–disorder phase transition (ca. 155 K) observed in the mixed-valence iron­(II)–iron­(III) formate framework compound [NH₂(CH₃)₂]_<i>n</i>[Fe^IIIFe^II(HCOO)₆]_<i>n</i>. The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order–disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe^IIIFe^II(HCOO)₆]_<i>n</i> framework. In the low-temperature phase, a change in space group from <i>P</i>3̅1<i>c</i> to <i>R</i>3̅<i>c</i> occurs, involving a tripling of the <i>c</i>-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe^II and Fe^III magnetic moments