Frustrated Lewis Pairs Comprising Nitrogen Lewis Acids for Si–H Bond Activation

N-heterocyclic nitrogen Lewis acids are a recent addition to the field of organic chemistry. Based on nitrenium cations, these acids where previously shown to generate Lewis adducts when combined with the appropriate Lewis bases. Herein, a triazinium-based Lewis acid was combined with tBu₃P to generate a frustrated Lewis pair (FLP) capable of cleaving, for the first time, Si−H bonds in silanes. Whereas low yields were initially encountered owing to insufficient Lewis acidity, a new nitrenium-based Lewis acid was synthesized, and its superior Lewis acidity was experimentally and computationally confirmed. A FLP based on this acid cleaved the Si−H bond in PhSiH₃, generating the triazane product in a quantitative yield. This unprecedented N−H triazane was fully characterized by multinuclear NMR techniques and single-crystal X-ray crystallography. A new class of compounds, N-H triazanes display the potential capacity to participate in hydride transfer reactions.     

NQR investigations of high-T c superconducting oxides

Nuclear quadrupole resonance (NQR) of⁶³Cu has been performed to study the electronic and magnetic properties of YBa₂Cu₃O_6.1 ceramics, treated in iodine or bromine vapours. An analysis of the NQR shows undistorted CuO₂ planes and the absence of an increase of the oxygen content in chains of Cu(1)-O in halogen treated Y-Ba-Cu-O ceramics.¹³⁹La NQR spin-lattice relaxation measurements in powdered La_2?x CuO_4?y compounds are also reported. The present results indicate that the¹³⁹La nuclear relaxation is dominated by the Cu⁺⁺-Cu⁺⁺ magnetic correlations.     

Investigation into phase diagrams of the fluorine-oxygen system: Ferroelastic-antiferroelectric (NH4)2WO2F4-(NH4)2MoO2F4

Thermal, physical, structural, optical, and dielectric investigations have been performed for oxyfluoride solid solutions (NH₄)₂W_{1 — x} Mo _x O₂F₄ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1). The character of the influence of the chemical and hydrostatic pressures on the stability of the parent (space group Cmcm) and distorted ferroelastic and antiferroelectric phases has been determined by analyzing the temperature-pressure, unit cell volume-composition, and temperature-composition phase diagrams. The specific features of the nature and mechanism of the phase transitions have been discussed using the available data on the structural, entropy, and dielectric parameters.     

Effect of Deuteration on Phase Transitions in Vanadium Dioxotetrafluoride

Physics of the Solid State - The crystals of (ND4)3VO2F4 with a high degree of deuteration (~87%) have been grown and a significant (~1.5%) increase in the unit cell volume has been detected. The...     

Thermodynamic Properties of Vanadium Oxypentafluoride (IV) (NH4)3VOF5

Physics of the Solid State - The (NH4)3VOF5 crystals have been synthesized and their homogeneity and single-phase structure has been established by the X-ray diffraction, energy dispersive...     

ChemInform Abstract: Structural Transformation Between Two Cubic Phases of (NH4)3SnF7.

Single crystals of (NH₄)₃SnF₇ are obtained from aqueous solutions of (NH₄)₂SnF₆ and excess NH₄F during solvent evaporation.     

Ordering of oxygen in halogen treated 1-2-3 systems as studied by NQR

We have investigated the low-temperature behavior of Cu NQR for iodinated RBa₂Cu₃O _x (R = Y, Gd) compounds. The different influence of Gd spins on the Cu(1) and Cu(2) sites was used to separate the contributions of both sites in the spectra. The distinct NQR lines associated with the different oxygen-coordinated Cu(1) sites have been observed. The NQR spectra of the Cu(1) sites show that the iodine treatment gives rise to the modifications of the oxygen sublattice. From the analysis of the NQR spectra of the Cu(1) sites follows an increase of the average length of the Cu(1)-O chains at treatment.     

Phase transitions and thermodynamic properties of (NH4)3VO2F4 cryolite

Calorimetric measurements performed in a wide temperature range on (NH₄)₃VO₂F₄ have shown the presence of four heat capacity anomalies at T₁ = 438 K, T₂ = 244 K, T₃ = 210.2 K, T₄ = 205.1 K associated with the first order phase transitions. In accordance with the permittivity behavior, the structural transformations are of nonferroelectric nature. Pressure dependence of the phase transition temperatures has been studied by DTA under pressure. The entropy of phase transitions is analyzed mainly in the framework of the orientational disordering of NH₄⁺ and VO₂F₄^3? ions in a cubic phase.