Crystal structure solution of a high-pressure polymorph of scintillating MgMoO4 and its electronic structure

The structure of the potentially scintillating high-pressure phase of [Beta] - MgMoO 4 ( γ - MgMoO 4 ) has been solved by means of high-pressure single-crystal x-ray diffraction. The phase transition occurs above 1.5 GPa and involves an increase of the Mo coordination from fourfold to sixfold accommodated by a rotation of the polyhedra and a concommitant bond stretching resulting in an enlargement of the c axis. A previous high-pressure Raman study had proposed such changes with a symmetry change to space group P 2 / c . Here it has been found that the phase transition is isosymmetrical ( C 2 / m -> C 2 / m ). The bulk moduli and the compressibilities of the crystal axes of both the low- and the high-pressure phase, have been obtained from equation of state fits to the pressure evolution of the unit-cell parameters which were obtained from powder x-ray diffraction up to 12 GPa. The compaction of the crystal structure at the phase transition involves a doubling of the bulk modulus B 0 changing from 60.3(1) to 123.7(8) GPa and a change of the most compressible crystal axis from the (0, b , 0) direction in [Beta] - MgMoO 4 to the ( 0.9 a , 0, 0.5 a ) direction in γ - MgMoO 4 . The lattice dynamical calculations performed here on γ - MgMoO 4 served to explain the Raman spectra observed for the high-pressure phase of [Beta] - MgMoO 4 in a previous work demonstrating that the use of internal modes arguments in which the MoO n polyhedra are considered as separate vibrational units fails at least in this molybdate. The electronic structure of γ - MgMoO 4 was also calculated and compared with the electronic structures of [Beta] - MgMoO 4 and MgWO 4 shedding some light on why MgWO 4 is a much better scintillator than any of the phases of MgMoO 4 . These calculations yielded for γ - MgMoO 4 a Y 2 Γ -> Γ indirect band gap of 3.01 eV in contrast to the direct bandgaps of [Beta] - MgMoO 4 (3.58 eV at Γ ) and MgWO 4 (3.32 eV at Z ).The authors thank I. Collings and M. Handfland from the ID15B beamline at the ESRF for their help during the experiments, and O. Gomis from the Universitat Politècnica de València for the discussions. Most of the work presented in this work benefited from the financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN) under Projects No. PID2019- 106383GB-C41/43 (MCIN/AEI/10.13039/501100011033), MALTA Consolider-Team network RED2018-102612- T (MINECO/AEI/10.13039/501100003329), and from the Generalitat Valenciana under Project PROMETEO/2018/123. V.M. also thanks the MICINN for the Beatriz Galindo distinguished researcher program (BG20/00077)

Isolierung und Reaktivität eines s-Block-Metall-Antiaromaten

Das Konzept der Aromatizität und der Antiaromatizität ist seit langem bekannt, und zahlreiche Belege für dieses Phänomen wurden durch Moleküle, welche auf Elementen des p-, d- und f-Blocks des Periodensystems der Elemente (PSE) basieren, geliefert. Aufgrund der begrenzten Varianz des Oxidationszustandes von s-Block-Metallen konnten diese bisher nicht mit komplexen π-Bindungssystemen interagieren. Daher gibt es keine bzw. nur schlecht beschriebene Beispiele für antiaromatische Systeme mit s-Block-Metallen. Durch die Verwendung von spektroskopischen, strukturanalytischen und quantenchemischen Methoden konnte eine heterocyclische Verbindung hergestellt und charakterisiert werden, welche das Erdalkalimetall Beryllium enthält und signifikante Antiaromatizität aufweist. Weiterhin beschreiben wir die Reaktivität gegenüber Lewis-Basen und die chemische Reduktion dieser Verbindung

4-[(2E)-2-(4-Chlorobenzylidene)hydrazinylidene]-1-methyl-1, 4-dihydro-pyridine monohydrate

In the title compound, C13H12ClN3· H2O, the organic mol-ecule is almost planar, with a dihedral angle of 3.22 (10)° between the benzene and pyridine rings. The crystal structure is stabilized by O - H?N and C - H?O hydrogen bonding and ?-? stacking inter-actions [centroid-centroid distances = 3.630 (1) and 3.701 (1) Å]

Uranium Hydridoborates: Synthesis, Magnetism, and X-ray/Neutron Diffraction Structures

While uranium hydridoborate complexes containing the [BH₄]⁻ moiety have been well-known in the literature for many years, species with functionalized borate centers remained considerably rare. We were now able to prepare several uranium hydridoborates (<b>1–4</b>) with amino-substituted borate moieties with high selectivity by smooth reaction of [Cp*₂UMe₂] (Cp* = C₅Me₅) and [Cp′₂UMe₂] (Cp′ = 1,2,4-<i>t</i>Bu₃C₅H₂) with the aminoborane H₂BN­(SiMe₃)₂. A combination of nuclear magnetic resonance spectroscopy, deuteration experiments, magnetic SQUID measurements, and X-ray/neutron diffraction studies was used to verify the anticipated molecular structures and oxidation states of <b>1–4</b> and helped to establish a linear tridentate coordination mode of the borate anions