Clathration of Five-Membered Aromatic Rings in the Bimetallic Spin Crossover Metal–Organic Framework [Fe(TPT)_2/3{M^I(CN)₂}₂]·G (M^I = Ag, Au)

Six clathrate compounds of the three-dimensional spin crossover metal–organic framework formulated [Fe­(TPT)_2/3­{M^I(CN)₂}₂]·nG, where TPT is 2,4,6-tris­(4-pyridyl)-1,3,5-triazine, M^I = Ag or Au and G represent the guest molecules furan, pyrrole and thiophene, were synthesized using slow diffusion techniques. The clathrate compounds were characterized by single-crystal X-ray diffraction at 120 and 300 K, thermogravimetric analysis and thermal dependence of the magnetic susceptibility. All compounds crystallize in the <i>R</i>3̅<i>m</i> trigonal space group. The Fe^II defines a unique [FeN₆] crystallographic site with the equatorial positions occupied by four dicyanometallate ligands while the axial positions are occupied by the TPT ligands. Each TPT ligand links three Fe^II sites, while the dicyanometallate ligands bridge two Fe^II sites thereby generating two interlocked three-dimensional frameworks with the NbO topology. The choice of the TPT ligand favors the generation of pores where the guest molecules are located. The thermal dependence of the magnetic susceptibility of samples constituted of single crystals was investigated for the six compounds to assess the influence of the guest molecules on the spin crossover behavior. In general, the magnetic properties of the six clathrates suggest a gradual stabilization of the high-spin state as the molecular volume of the guest increases

Clathration of Five-Membered Aromatic Rings in the Bimetallic Spin Crossover Metal–Organic Framework [Fe(TPT)_2/3{M^I(CN)₂}₂]·G (M^I = Ag, Au)

Six clathrate compounds of the three-dimensional spin crossover metal–organic framework formulated [Fe­(TPT)_2/3­{M^I(CN)₂}₂]·nG, where TPT is 2,4,6-tris­(4-pyridyl)-1,3,5-triazine, M^I = Ag or Au and G represent the guest molecules furan, pyrrole and thiophene, were synthesized using slow diffusion techniques. The clathrate compounds were characterized by single-crystal X-ray diffraction at 120 and 300 K, thermogravimetric analysis and thermal dependence of the magnetic susceptibility. All compounds crystallize in the <i>R</i>3̅<i>m</i> trigonal space group. The Fe^II defines a unique [FeN₆] crystallographic site with the equatorial positions occupied by four dicyanometallate ligands while the axial positions are occupied by the TPT ligands. Each TPT ligand links three Fe^II sites, while the dicyanometallate ligands bridge two Fe^II sites thereby generating two interlocked three-dimensional frameworks with the NbO topology. The choice of the TPT ligand favors the generation of pores where the guest molecules are located. The thermal dependence of the magnetic susceptibility of samples constituted of single crystals was investigated for the six compounds to assess the influence of the guest molecules on the spin crossover behavior. In general, the magnetic properties of the six clathrates suggest a gradual stabilization of the high-spin state as the molecular volume of the guest increases

Homoleptic Iron(II) Complexes with the Ionogenic Ligand 6,6′-Bis(1<i>H</i>‑tetrazol-5-yl)-2,2′-bipyridine: Spin Crossover Behavior in a Singular 2D Spin Crossover Coordination Polymer

Deprotonation of the ionogenic tetradentate ligand 6,6′-bis­(1<i>H</i>-tetrazol-5-yl)-2,2′-bipyridine [H₂bipy­(ttr)₂] in the presence of Fe^II in solution has afforded an anionic mononuclear complex and a neutral two-dimensional coordination polymer formulated as, respectively, NEt₃H­{Fe­[bipy­(ttr)₂]­[Hbipy­(ttr)₂]}·3MeOH (<b>1</b>) and {Fe­[bipy­(ttr)₂]}<i>_n</i> (<b>2</b>). The anions [Hbipy­(ttr)₂]⁻ and [bipy­(ttr)₂]^2– embrace the Fe^II centers defining discrete molecular units <b>1</b> with the Fe^II ion lying in a distorted bisdisphenoid dodecahedron, a rare example of octacoordination in the coordination environment of this cation. The magnetic behavior of <b>1</b> shows that the Fe^II is high-spin, and its Mössbauer spectrum is characterized by a relatively large average quadrupole splitting, Δ<i>E</i>_Q = 3.42 mm s^–1. Compound <b>2</b> defines a strongly distorted octahedral environment for Fe^II in which one [bipy­(ttr)₂]⁻ anion coordinates the equatorial positions of the Fe^II center, while the axial positions are occupied by peripheral <i>N</i>-tetrazole atoms of two adjacent {Fe­[bipy­(ttr)₂]}⁰ moieties thereby generating an infinite double-layer sheet. Compound <b>2</b> undergoes an almost complete spin crossover transition between the high-spin and low-spin states centered at about 221 K characterized by an average variation of enthalpy and entropy Δ<i>H</i>^av = 8.27 kJ mol^–1, Δ<i>S</i>^av = 37.5 J K^–1 mol^–1, obtained from calorimetric DSC measurements. Photomagnetic measurements of <b>2</b> at 10 K show an almost complete light-induced spin state trapping (LIESST) effect which denotes occurrence of antiferromagnetic coupling between the excited high-spin species and <i>T</i>_LIESST = 52 K. The crystal structure of <b>2</b> has been investigated in detail at various temperatures and discussed

The role of effectors of the activin signalling pathway, activin receptors IIA and IIB, and Smad2, in patterning of tooth development

The synthesis, crystal structures, magnetic behavior, and electron paramagnetic resonance studies of five new Fe^III spin crossover (SCO) complexes are reported. The [Fe^IIIN₅O] coordination core is constituted of the pentadentate ligand bztpen (N₅) and a series of alkoxide anions (ethoxide, propoxide, <i>n</i>-butoxide, isobutoxide, and ethylene glycoxide). The methoxide derivative previously reported by us is also reinvestigated. The six complexes crystallize in the orthorhombic <i>Pbca</i> space group and show similar molecular structures and crystal packing. The coordination octahedron is strongly distorted in both the high- and low-temperature structures. The structural changes upon spin conversion are consistent with those previously observed for [Fe^IIIN₄O₂] SCO complexes of the Schiff base type, except for the Fe–O­(alkoxide) bond distance, which shortens significantly in the high-spin state. Application of the Slichter–Drickamer thermodynamic model to the experimental SCO curves afforded reasonably good simulations with typical enthalpy and entropy variations ranging in the intervals Δ<i>H</i> = 6–13 kJ mol^–1 and Δ<i>S</i> = 40–50 J mol^–1 K^–1, respectively. The estimated values of the cooperativity parameter Γ, found in the interval 0–2.2 kJ mol^–1, were consistent with the nature of the SCO. Electron paramagnetic resonance spectroscopy confirmed the transformation between the high-spin and low-spin states, characterized by signals at <i>g</i> ≈ 4.47 and 2.10, respectively. Electrochemical analysis demonstrated the instability of the Fe­(II) alkoxide derivatives in solution

Exploiting Pressure To Induce a “Guest-Blocked” Spin Transition in a Framework Material

A new functionalized 1,2,4-triazole ligand, 4-[(<i>E</i>)-2-(5-methyl-2-thienyl)­vinyl]-1,2,4-triazole (thiome), was prepared to assess the broad applicability of strategically producing multistep spin transitions in two-dimensional Hofmann-type materials of the type [Fe^IIPd­(CN)₄(R-1,2,4-trz)₂]·<i>n</i>H₂O (R-1,2,4-trz = a 4-functionalized 1,2,4-triazole ligand). A variety of structural and magnetic investigations on the resultant framework material [Fe^IIPd­(CN)₄(thiome)₂]·2H₂O (<b>A·2H</b>_<b>2</b><b>O</b>) reveal that a high-spin (HS) to low-spin (LS) transition is inhibited in <b>A·2H</b>_<b>2</b><b>O</b> due to a combination of guest and ligand steric bulk effects. The water molecules can be reversibly removed with retention of the porous host framework and result in the emergence of an abrupt and hysteretic one-step spin transition due to the removal of guest internal pressure. A spin transition can, furthermore, be induced in <b>A·2H</b>_<b>2</b><b>O</b> (0–0.68 GPa) under hydrostatic pressure, as evidenced by variable-pressure structure and magnetic studies, resulting in a two-step spin transition at ambient temperatures at 0.68 GPa. The presence of a two-step spin crossover (SCO) in <b>A·2H</b>_<b>2</b><b>O</b> under hydrostatic pressure compared to a one-step SCO in <b>A</b> at ambient pressure is discussed in terms of the relative ability of each phase to accommodate mixed HS/LS states according to differing lattice flexibilities

Spin Crossover-Assisted Modulation of Electron Transport in a Single-Crystal 3D Metal–Organic Framework

Molecule-based spin crossover (SCO) materials display likely one of the most spectacular switchable processes. The SCO involves reversible changes in their physicochemical properties (i.e. optical, magnetic, electronic, and elastic) that are coupled with the spin-state change under an external perturbation (i.e. temperature, light, magnetic field, or the inclusion/release of analytes). Although very promising for their future integration into electronic devices, most SCO compounds show two major drawbacks: (i) their intrinsic low conductance and (ii) the unclear mechanism connecting the spin-state change and the electrical conductivity. Herein, we report the controlled single-crystal-to-single-crystal temperature-induced transformation in a robust metal–organic framework, [Fe2(H0.67bdt)3]·9H2O (1), being bdt2– = 1,4-benzeneditetrazolate, exhibiting a dynamic spin-state change concomitant with an increment in the anisotropic electrical conductance. Compound 1 remains intact during the SCO process even after approximately a 15% volume reduction. The experimental findings are rationalized by analyzing the electronic delocalization of the frontier states by means of density-functional theory calculations. The results point to a correlation between the spin-state of the iron and the electronic conductivity of the 3D structure. In addition, the reversibility of the process is proved

Spin Crossover-Assisted Modulation of Electron Transport in a Single-Crystal 3D Metal–Organic Framework

Molecule-based spin crossover (SCO) materials display likely one of the most spectacular switchable processes. The SCO involves reversible changes in their physicochemical properties (i.e. optical, magnetic, electronic, and elastic) that are coupled with the spin-state change under an external perturbation (i.e. temperature, light, magnetic field, or the inclusion/release of analytes). Although very promising for their future integration into electronic devices, most SCO compounds show two major drawbacks: (i) their intrinsic low conductance and (ii) the unclear mechanism connecting the spin-state change and the electrical conductivity. Herein, we report the controlled single-crystal-to-single-crystal temperature-induced transformation in a robust metal–organic framework, [Fe2(H0.67bdt)3]·9H2O (1), being bdt2– = 1,4-benzeneditetrazolate, exhibiting a dynamic spin-state change concomitant with an increment in the anisotropic electrical conductance. Compound 1 remains intact during the SCO process even after approximately a 15% volume reduction. The experimental findings are rationalized by analyzing the electronic delocalization of the frontier states by means of density-functional theory calculations. The results point to a correlation between the spin-state of the iron and the electronic conductivity of the 3D structure. In addition, the reversibility of the process is proved

Spin Crossover-Assisted Modulation of Electron Transport in a Single-Crystal 3D Metal–Organic Framework

Molecule-based spin crossover (SCO) materials display likely one of the most spectacular switchable processes. The SCO involves reversible changes in their physicochemical properties (i.e. optical, magnetic, electronic, and elastic) that are coupled with the spin-state change under an external perturbation (i.e. temperature, light, magnetic field, or the inclusion/release of analytes). Although very promising for their future integration into electronic devices, most SCO compounds show two major drawbacks: (i) their intrinsic low conductance and (ii) the unclear mechanism connecting the spin-state change and the electrical conductivity. Herein, we report the controlled single-crystal-to-single-crystal temperature-induced transformation in a robust metal–organic framework, [Fe2(H0.67bdt)3]·9H2O (1), being bdt2– = 1,4-benzeneditetrazolate, exhibiting a dynamic spin-state change concomitant with an increment in the anisotropic electrical conductance. Compound 1 remains intact during the SCO process even after approximately a 15% volume reduction. The experimental findings are rationalized by analyzing the electronic delocalization of the frontier states by means of density-functional theory calculations. The results point to a correlation between the spin-state of the iron and the electronic conductivity of the 3D structure. In addition, the reversibility of the process is proved

Spin Crossover-Assisted Modulation of Electron Transport in a Single-Crystal 3D Metal–Organic Framework

Molecule-based spin crossover (SCO) materials display likely one of the most spectacular switchable processes. The SCO involves reversible changes in their physicochemical properties (i.e. optical, magnetic, electronic, and elastic) that are coupled with the spin-state change under an external perturbation (i.e. temperature, light, magnetic field, or the inclusion/release of analytes). Although very promising for their future integration into electronic devices, most SCO compounds show two major drawbacks: (i) their intrinsic low conductance and (ii) the unclear mechanism connecting the spin-state change and the electrical conductivity. Herein, we report the controlled single-crystal-to-single-crystal temperature-induced transformation in a robust metal–organic framework, [Fe2(H0.67bdt)3]·9H2O (1), being bdt2– = 1,4-benzeneditetrazolate, exhibiting a dynamic spin-state change concomitant with an increment in the anisotropic electrical conductance. Compound 1 remains intact during the SCO process even after approximately a 15% volume reduction. The experimental findings are rationalized by analyzing the electronic delocalization of the frontier states by means of density-functional theory calculations. The results point to a correlation between the spin-state of the iron and the electronic conductivity of the 3D structure. In addition, the reversibility of the process is proved