Anion–Anion Bonding and Topology in Ternary Iridium Seleno–Stannides

The synthesis and physical properties of two new and one known Ir–Sn–Se compound are reported. Their crystal structures are elucidated with transmission electron microscopy and powder X-ray diffraction. IrSn_0.45Se_1.55 is a pyrite phase which consists of tilted corner-sharing Ir<i>X</i>₆ octahedra with randomly distributed (Sn–Se)^4– and (Se–Se)^2– dimers. Ir₂Sn₃Se₃ is a known trigonally distorted skutterudite that consists of cooperatively tilted corner-sharing IrSn₃Se₃ octahedra with ordered (Sn–Se)₂^4– tetramers. Ir₂SnSe₅ is a layered, distorted β-MnO₂ (pyrolusite) structure consisting of a double IrSe₆ octrahedral row, corner sharing in the <i>a</i> direction and edge sharing in the <i>b</i> direction. This distorted pyrolusite contains (Se–Se)^2– dimers and Se^2– anions, and each double row is “capped” with a (Sn–Se)_<i>n</i> polymeric chain. Resistivity, specific heat, and magnetization measurements show that all three have insulating and diamagnetic behavior, indicative of low-spin 5d⁶ Ir³⁺. Electronic structure calculations on Ir₂Sn₃Se₃ show a <i>single,</i> spherical, nonspin–orbit split valence band and suggest that Ir₂Sn₃Se₃ is topologically nontrivial under tensile strain due to inversion of Ir-d and Se-p states

Selective Gas Adsorption in Highly Porous Chromium(II)-Based Metal–Organic Polyhedra

Selective Gas Adsorption in Highly Porous Chromium(II)-Based Metal–Organic Polyhedr

Flexing of a Metal–Organic Framework upon Hydrocarbon Adsorption: Atomic Level Insights from Neutron Scattering

Metal–organic frameworks (MOFs) offer considerable opportunities for gas uptake, storage, and separation due to their porosity, chemical tunability, and flexibility. Flexible MOFs undergo reversible structural transformations triggered by external stimuli such as adsorption of specific guest molecules. The MUF-16 family of materials has exceptional gas adsorption properties including selective uptake of carbon dioxide over other gases. We observed one member of this family, MUF-16(Mn), to be flexible upon the adsorption of hydrocarbon gases. We used a combination of in situ synchrotron X-ray and neutron diffraction to identify the framework–gas interactions that underlie the structural flexibility. Inelastic neutron scattering, along with calculations, also enables an understanding of the dynamics of the flexibility. In essence, C3 hydrocarbons effectively bridge across hydrogen-bonded carboxyl dimers in the framework, triggering pore expansion and inhibiting certain types of motion in the framework

Flexing of a Metal–Organic Framework upon Hydrocarbon Adsorption: Atomic Level Insights from Neutron Scattering

Metal–organic frameworks (MOFs) offer considerable opportunities for gas uptake, storage, and separation due to their porosity, chemical tunability, and flexibility. Flexible MOFs undergo reversible structural transformations triggered by external stimuli such as adsorption of specific guest molecules. The MUF-16 family of materials has exceptional gas adsorption properties including selective uptake of carbon dioxide over other gases. We observed one member of this family, MUF-16(Mn), to be flexible upon the adsorption of hydrocarbon gases. We used a combination of in situ synchrotron X-ray and neutron diffraction to identify the framework–gas interactions that underlie the structural flexibility. Inelastic neutron scattering, along with calculations, also enables an understanding of the dynamics of the flexibility. In essence, C3 hydrocarbons effectively bridge across hydrogen-bonded carboxyl dimers in the framework, triggering pore expansion and inhibiting certain types of motion in the framework

Nature of Decahydro-<i>closo</i>-decaborate Anion Reorientations in an Ordered Alkali-Metal Salt: Rb₂B₁₀H₁₀

The ordered monoclinic phase of the alkali-metal decahydro-<i>closo</i>-decaborate salt Rb₂B₁₀H₁₀ was found to be stable from about 250 K all the way up to an order–disorder phase transition temperature of ≈762 K. The broad temperature range for this phase allowed for a detailed quasielastic neutron scattering (QENS) and nuclear magnetic resonance (NMR) study of the protypical B₁₀H₁₀^2– anion reorientational dynamics. The QENS and NMR combined results are consistent with an anion reorientational mechanism comprised of two types of rotational jumps expected from the anion geometry and lattice structure, namely, more rapid 90° jumps around the anion <i>C</i>₄ symmetry axis (e.g., with correlation frequencies of ≈2.6 × 10¹⁰ s^–1 at 530 K) combined with order of magnitude slower orthogonal 180° reorientational flips (e.g., ≈3.1 × 10⁹ s^–1 at 530 K) resulting in an exchange of the apical H (and apical B) positions. Each latter flip requires a concomitant 45° twist around the <i>C</i>₄ symmetry axis to preserve the ordered Rb₂B₁₀H₁₀ monoclinic structural symmetry. This result is consistent with previous NMR data for ordered monoclinic Na₂B₁₀H₁₀, which also pointed to two types of anion reorientational motions. The QENS-derived reorientational activation energies are 197(2) and 288(3) meV for the <i>C</i>₄ fourfold jumps and apical exchanges, respectively, between 400 and 680 K. Below this temperature range, NMR (and QENS) both indicate a shift to significantly larger reorientational barriers, for example, 485(8) meV for the apical exchanges. Finally, subambient diffraction measurements identify a subtle change in the Rb₂B₁₀H₁₀ structure from monoclinic to triclinic symmetry as the temperature is decreased from around 250 to 210 K

Nature of Decahydro-<i>closo</i>-decaborate Anion Reorientations in an Ordered Alkali-Metal Salt: Rb₂B₁₀H₁₀

The ordered monoclinic phase of the alkali-metal decahydro-<i>closo</i>-decaborate salt Rb₂B₁₀H₁₀ was found to be stable from about 250 K all the way up to an order–disorder phase transition temperature of ≈762 K. The broad temperature range for this phase allowed for a detailed quasielastic neutron scattering (QENS) and nuclear magnetic resonance (NMR) study of the protypical B₁₀H₁₀^2– anion reorientational dynamics. The QENS and NMR combined results are consistent with an anion reorientational mechanism comprised of two types of rotational jumps expected from the anion geometry and lattice structure, namely, more rapid 90° jumps around the anion <i>C</i>₄ symmetry axis (e.g., with correlation frequencies of ≈2.6 × 10¹⁰ s^–1 at 530 K) combined with order of magnitude slower orthogonal 180° reorientational flips (e.g., ≈3.1 × 10⁹ s^–1 at 530 K) resulting in an exchange of the apical H (and apical B) positions. Each latter flip requires a concomitant 45° twist around the <i>C</i>₄ symmetry axis to preserve the ordered Rb₂B₁₀H₁₀ monoclinic structural symmetry. This result is consistent with previous NMR data for ordered monoclinic Na₂B₁₀H₁₀, which also pointed to two types of anion reorientational motions. The QENS-derived reorientational activation energies are 197(2) and 288(3) meV for the <i>C</i>₄ fourfold jumps and apical exchanges, respectively, between 400 and 680 K. Below this temperature range, NMR (and QENS) both indicate a shift to significantly larger reorientational barriers, for example, 485(8) meV for the apical exchanges. Finally, subambient diffraction measurements identify a subtle change in the Rb₂B₁₀H₁₀ structure from monoclinic to triclinic symmetry as the temperature is decreased from around 250 to 210 K

Nature of Decahydro-<i>closo</i>-decaborate Anion Reorientations in an Ordered Alkali-Metal Salt: Rb₂B₁₀H₁₀

The ordered monoclinic phase of the alkali-metal decahydro-<i>closo</i>-decaborate salt Rb₂B₁₀H₁₀ was found to be stable from about 250 K all the way up to an order–disorder phase transition temperature of ≈762 K. The broad temperature range for this phase allowed for a detailed quasielastic neutron scattering (QENS) and nuclear magnetic resonance (NMR) study of the protypical B₁₀H₁₀^2– anion reorientational dynamics. The QENS and NMR combined results are consistent with an anion reorientational mechanism comprised of two types of rotational jumps expected from the anion geometry and lattice structure, namely, more rapid 90° jumps around the anion <i>C</i>₄ symmetry axis (e.g., with correlation frequencies of ≈2.6 × 10¹⁰ s^–1 at 530 K) combined with order of magnitude slower orthogonal 180° reorientational flips (e.g., ≈3.1 × 10⁹ s^–1 at 530 K) resulting in an exchange of the apical H (and apical B) positions. Each latter flip requires a concomitant 45° twist around the <i>C</i>₄ symmetry axis to preserve the ordered Rb₂B₁₀H₁₀ monoclinic structural symmetry. This result is consistent with previous NMR data for ordered monoclinic Na₂B₁₀H₁₀, which also pointed to two types of anion reorientational motions. The QENS-derived reorientational activation energies are 197(2) and 288(3) meV for the <i>C</i>₄ fourfold jumps and apical exchanges, respectively, between 400 and 680 K. Below this temperature range, NMR (and QENS) both indicate a shift to significantly larger reorientational barriers, for example, 485(8) meV for the apical exchanges. Finally, subambient diffraction measurements identify a subtle change in the Rb₂B₁₀H₁₀ structure from monoclinic to triclinic symmetry as the temperature is decreased from around 250 to 210 K