Annual Catalogue of the Minnesota State Normal School at Moorhead. Seventh Year. (1894-1895)

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Modulation of the Slow Relaxation of the Magnetization Dynamics through Second Coordination Sphere in Macrocyclic Dysprosium(III) Complexes

Single-molecule magnets (SMMs) exhibit unique magnetic properties related to the molecular nature of these “isolated” coordination complexes. In this study, we investigate the influence of counterions on two macrocyclic dysprosium-based SMMs, namely, [DyLN6(OAc)2][OAc] (1) and [DyLN6(OAc)2][B(C6H5)4] (2) (LN6 = 2,7,13,18-tetramethyl-3,6,14,17,23,24-hexaazatricyclo[17.3.1.18,12]tetracosa 1(23),2,6,8,10,12(24),13,17,19,21-decaene, OAc = acetate), differing by the nature of the counterion. We demonstrate that the nature of the counterion indirectly modulates the degree of coordination geometry distortion, particularly in macrocycle folding, through subtle intermolecular interactions. This subsequently affects the slow relaxation dynamics, as supported by both magnetic and theoretical calculations. A noticeable decrease in the transverse magnetic anisotropy is observed for 2, attributed to a reduced degree of macrocycle distortion in the equatorial plane. Theoretical calculations further suggest a greater crystal-field splitting in 2 with the first excited state estimated to be twice as large in energy compared to 1. Both complexes exhibit magnetization relaxation dynamics primarily driven by a Raman process

Pressure-Induced Insertion of Ammonia Borane in the Siliceous Zeolite, Silicalite-1F

A combination of Raman spectroscopy and X-ray diffraction was used to investigate the insertion of ammonia borane in the 5.5 Å diameter pores of the hydrophobic, all-silica zeolite, silicalite-1F in the pressure range up to 4.8 GPa. Insertion and nanoconfinement result in the appearance of new Raman modes, especially in the N–H stretching region and significant changes in the intensities and pressure dependencies of a large number of other modes. Orientational disorder of the −BH₃ and −NH₃ groups persists to higher pressures in nanoconfined as compared to the bulk ammonia borane. The structure of the recovered sample was determined by single crystal X-ray diffraction. Each pore in the unit cell was found to contain between 2 and 3 molecules of ammonia borane forming single-molecule chains due to the spatial constraints. In situ, high pressure, X-ray powder diffraction indicated that the compressibility of the ammonia borane-silicalite-1F composite is three times lower than that of empty silicalite-1F due to pore filling. These results show that silicalite-1F can be a suitable nanoscaffold for this important chemical hydrogen-storage material

Mechanism of H₂O Insertion and Chemical Bond Formation in AlPO₄‑54·<i>x</i>H₂O at High Pressure

The insertion of H₂O in AlPO₄-54·<i>x</i>H₂O at high pressure was investigated by single-crystal X-ray diffraction and Monte Carlo molecular simulation. H₂O molecules are concentrated, in particular, near the pore walls. Upon insertion, the additional water is highly disordered. Insertion of H₂O (superhydration) is found to impede pore collapse in the material, thereby strongly modifying its mechanical behavior. However, instead of stabilizing the structure with respect to amorphization, the results provide evidence for the early stages of chemical bond formation between H₂O molecules and tetrahedrally coordinated aluminum, which is at the origin of the amorphization/reaction process

Saturation of the Siliceous Zeolite TON with Neon at High Pressure

The insertion of neon and argon in the 1-D pore system of the zeolite TON was studied at high pressure by X-ray diffraction and by Monte Carlo (MC) molecular modeling. Rietveld refinements of the crystal structure of TON and the MC results indicate that 12 Ne atoms enter the unit cell of TON, completely filling the pores. This is much greater than the degree of filling observed for argon, which due to size considerations lies in a vertical plane in the pores. A phase transition from the <i>Cmc</i>2₁ to a <i>Pbn</i>2₁ structure occurs at 0.6 GPa with cell doubling. The compressibility and structural distortions, such as pore ellipticity, are considerably reduced as compared to the argon-filled or the empty-pore material. In addition, the crystalline form persists to pressures of the order of 20 GPa, and the <i>Pbn</i>2₁ phase is recovered after decompression. The results show the very strong and different effects of pore filling by noble gases on the structural stability and mechanical properties of this prototypical 1-D zeolite-type material

High-Pressure Phase Transition, Pore Collapse, and Amorphization in the Siliceous 1D Zeolite, TON

The siliceous zeolite TON with a 1-D pore system was studied at high pressure by X-ray diffraction, infrared spectroscopy, and DFT calculations. The behavior of this material was investigated using nonpenetrating pressure-transmitting media. Under these conditions, a phase transition from the <i>Cmc</i>2₁ to a <i>Pbn</i>2₁ structure occurs at close to 0.6 GPa with doubling of the primitive unit cell based on Rietveld refinements. The pores begin to collapse with a strong increase in their ellipticity. Upon decreasing the pressure below this value the initial structure was not recovered. DFT calculations indicate that the initial empty pore <i>Cmc</i>2₁ phase is dynamically unstable. Irreversible, progressive pressure-induced amorphization occurs upon further increases in pressure up to 21 GPa. These changes are confirmed in the mid- and far-infrared spectra by peak splitting at the <i>Cmc</i>2₁ to <i>Pbn</i>2₁ phase transition and strong peak broadening at high pressure due to amorphization