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)

Magnetic Structures of Heterometallic M(II)–M(III) Formate Compounds

A study of the magnetic structure of the [NH₂(CH₃)₂]_<i>n</i>[Fe^IIIM^II(HCOO)₆]_<i>n</i> niccolite-like compounds, with M^II = Co^II (<b>2</b>) and Mn^II (<b>3</b>) ions, has been carried out using neutron diffraction and compared with the previously reported Fe^II-containing compound (<b>1</b>). The inclusion of two different metallic atoms into the niccolite-like structure framework leads to the formation of isostructural compounds with very different magnetic behaviors due to the compensation or not of the different spins involved in each lattice. Below <i>T</i>_N, the magnetic order in these compounds varies from ferrimagnetic behavior for <b>1</b> and <b>2</b> to an antiferromagnetic behavior with a weak spin canting for <b>3</b>. Structure refinements of <b>2</b> and <b>3</b> at low temperature (45 K) have been carried out combining synchrotron X-ray and high-resolution neutron diffraction in a multipattern approach. The magnetic structures have been determined from the difference patterns between the neutron data in the paramagnetic and the magnetically ordered regions. These difference patterns have been analyzed using a simulated annealing protocol and symmetry analysis techniques. The obtained magnetic structures have been further rationalized by means of ab initio DFT calculations. The direction of the magnetic moment of each compound has been determined. The easy axis of the M^II for compound <b>1</b> (Fe^II) is along the <i>c</i> axis; for compound <b>2</b> (Co^II), the moments are mainly within the <i>ab</i> plane; finally, for compound <b>3</b> (Mn^II), the calculations show that the moments have components both in the <i>ab</i> plane and along the <i>c</i> axis

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