In 1906, the preparation of “molybdic acid hydrate” was published by Arthur Rosenheim. Over the past 40 years, a multitude of isostructural compounds, which exist within a wide phase range of the system MoO3−NH3−H2O, have been published. The reported molecular formulas of “hexagonal molybdenum oxide” varied from MoO3 to MoO3·0.33NH3 to MoO3·nH2O (0.09 ≤ n ≤ 0.69) to MoO3·mNH3·nH2O (0.09 ≤ m ≤ 0.20; 0.18 ≤ n ≤ 0.60). Samples, prepared by the acidification route were investigated using thermal analysis coupled online to a mass spectrometer for evolved gas analysis, X-ray powder diffraction, Fourier transform infrared, Raman, magic-angle-spinning 1H- and 15N NMR spectroscopy, and incoherent inelastic neutron scattering. A comprehensive characterization of these samples will lead to a better understanding of their structure and physical properties as well as uncover the underlying relationship between the various compositions. The synthesized polymeric parent samples can be represented by the structural formula (NH4)(x∞)(3)[Mo(y square 1−y)O(3y)(OH)(x)(H2O)(m−n)]·nH2O with 0.10 ≤ x ≤ 0.14, 0.84 ≤ y ≤ 0.88, and m + n ≥ 3 − x − 3y. The X-ray study of a selected monocrystal confirmed the presence of the well-known 3D framework of edge- and corner-sharing MoO6 octahedra. The colorless monocrystal crystallizes in the hexagonal system with space group P6(3)/m, Z = 6, and unit cell parameters of a = 10.527(1) Å, c = 3.7245(7) Å, V = 357.44(8) Å3, and ρ = 3.73 g·cm(−3). The structure of the prepared monocrystal can best be described by the structural formula (NH4)(0.13∞)(3)[Mo(0.86 square 0.14)O2.58(OH)0.13(H2O)(0.29−n)]·nH2O, which is consistent with the existence of one vacancy (square) for six molybdenum sites. The sample MoO3·0.326NH3·0.343H2O, prepared by the ammoniation of a partially dehydrated MoO3·0.170NH3·0.153H2O with dry gaseous ammonia, accommodates NH3 in the hexagonal tunnels, in addition to [NH4]+ cations and H2O. The “chimie douce” reaction of MoO3·0.155NH3·0.440H2O with a 1:1 mixture of NO/NO2 at 100 °C resulted in the synthesis of MoO3·0.539H2O. This material is of great interest as a host of various molecules and cations.
Distortion of the static magnetic field inside the human head is dependent on regional tissue susceptibility variations and geometrical shape. These effects result in resonance line broadening and frequency shifts and consequently, intensity and spatial errors in both magnetic resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To calculate the field distortion due to the susceptibility's geometry, two dimensional (2D) finite element analysis was applied to simulate the field distribution in a 2D model of the human head, placed in a uniform magnetic field. The model contains air-filled cavities and sinuses, and the remainder is treated as water. The magnetic field deviation was evaluated using gray scale plots and histograms of the magnetic field. The shifts in parts/million and broadening of the histograms correspond to the NMR of the sampled region. The field distribution of the human head was also experimentally mapped using the DANTE tagging sequence. The calculated and experimental field maps are in good agreement. Thus, geometric considerations with uniform susceptibilities are sufficient to explain most of the static magnetic field distribution in the human head.
Several surface analytical techniques, including electron spectroscopy for chemical analysis (ESCA)(X-ray photoelectron spectroscopy) and sputtered neutral mass spectrometry (SNMS), were used to study the interaction between Hg and other components of fluorescent lamps, a very critical issue in lighting industries. Active sites, responsible for Hg interaction/deposition, can be successfully identified by comparing the x- y distribution (obtained by ESCA mapping) and depth distribution (available through SNMS) of respective lamp components with that of Hg. A correlation in both depth and x- y distribution is strong evidence of site preference for Hg interaction/deposition. A burial mechanism is, however, proposed when only depth distribution, not x- y, is correlated. Other modes of ESCA (high resolution, angle-resolved, etc.) were also helpful. Information about the valence states of the interacted Hg species would help to define the nature of the interaction.
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