Chemical Preparation,Thermal Behavior,Kinetic, and IR Studies of MnK4(P3O9)2.2H2O,Crystallographic Data of a New Cyclotriphosphate MnK4(P3O9)2, and Quantum Chemical Calculations for the P3O3− 9 Ion

Abstract

Chemical presparation, thermal behavior, and infrared (IR) studies are discussed for the cyclotriphosphate MnK₄(P₃O₉)₂.2H₂O and its anhydrous form MnK₄(P₃O₉)₂. The total dehydration of MnK₄(P₃O₉)₂.2H₂O, between 200 and 550 °C, leads to its anhydrous form MnK₄(P₃O₉)₂. MnK₄(P₃O₉)₂ is a new cyclotriphosphate crystallizing in the rhombohedral system and is stable until its melting point at 560 °C. The thermal behavior of MnK₄(P₃O₉)₂.2H₂O has been investigated and interpreted by comparison with IR absorption spectrometry and X-ray diffraction experiments. Two different methods, Ozawa and KAS (Kissinger-Akahira-Sunose), were selected in studying the kinetics of thermal behavior of the title compound. Quantum chemical calculations were made for the P₃O ^3? ₉ ion.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT     

White Emitters by Tuning the Excited‐State Intramolecular Proton‐Transfer Fluorescence Emission in 2‐(2′‐Hydroxybenzofuran)benzoxazole Dyes

The synthesis, structural, and photophysical properties of a new series of original dyes based on 2‐(2′‐hydroxybenzofuran)benzoxazole (HBBO) is reported. Upon photoexcitation, these dyes exhibit intense dual fluorescence with contribution from the enol (E*) and the keto (K*) emission, with K* being formed through excited‐state intramolecular proton transfer (ESIPT). We show that the ratio of emission intensity E*/K* can be fine‐tuned by judiciously decorating the molecular core with electron‐donating or ‐attracting substituents. Push–pull dyes 9 and 10 functionalized by a strong donor (nNBu₂) and a strong acceptor group (CF₃ and CN, respectively) exhibit intense dual emission, particularly in apolar solvents such as cyclohexane in which the maximum wavelength of the two bands is the more strongly separated. Moreover, all dyes exhibit strong solid‐state dual emission in a KBr matrix and polymer films with enhanced quantum yields reaching up to 54 %. A wise selection of substituents led to white emission both in solution and in the solid state. Finally, these experimental results were analyzed by time‐dependent density functional theory (TD‐DFT) calculations, which confirm that, on the one hand, only E* and K* emission are present (no rotamer) and, on the other hand, the relative free energies of the two tautomers in the excited state guide the ratio of the E*/K* emission intensities.     

First-principles calculations of helium and neon desorption from cavities in silicon

Combining density functional theory, the nudged elastic band technique, and the ultradense fluid model, we investigated the desorption process of He and Ne in silicon. Our results show that the internal surfaces of gas-filled bubbles are not a limiting factor during desorption experiments, since the surface reconstruction opens diffusion paths easier than in the bulk. We show that the vibrational contribution to the energy of helium in the bulk has to be considered in order to determine realistic pressures in the bubbles, when comparing experiments and simulations. At the maximum of desorption, an average pressure of 1-2 GPa is computed.     

Decomposition thermique et etude vibrationnelle de NiNa4(P3O9)2·6H2O

We have studied the dehydration and the calcination under atmospheric pressure of cyclotriphosphate tetrahydrate of nickel and sodium, NiNa₄(P₃O₉)₂·6H₂O, between 25 and 700°C by thermal analyses (TG, DTA) infrared spectrometry and X-ray diffraction. This study allows us the identification and the crystallographic characterization of a new phase, NiNa₄(PO₃)6, obtained between 350 and 450°C. NiNa₄(PO₃)₆ crystallizes in the triclinic system, P_–1, with the following unit cell parameters a=6.157(3) Å, b=6.820(6) Å, c=10.918(6) Å, =80.21(5)°, =97.80(9)°, =113.49(3)°, V=409.8 ų, Z=1, M(19)=25 and F(19)=48 (0.0095; 42). The calcination of NiNa₄(PO₃)₆, between 500 and 600°C, leads to a mixture of long-chain polyphosphates NiNa(PO₃)₃ and NaPO₃. The kinetic characteristics of the dehydration of NiNa₄(P₃O₉)₂·6H₂O were determined and discussed. The vibrational spectrum of the title compound, NiNa₄(P₃O₉)2·6H₂O, was interpreted in the domain of the stretching vibrations of the P₃O₉ rings, on the basis of its crystalline structure and in the light of the calculation of the normal IR frequencies of the P₃O₉ ring with D_3h symmetry.

This revised version was published online in November 2005 with corrections to the Cover Date.     

Polymer Nanocomposites: How to Reach Low Flammability?

The paper investigates critically the feasibility to make fire proof polymer using nanoparticles. It includes organoclay, polyhedral oligomeric silsesquioxanes (POSS) and carbon nanotube (CNT). It is shown that they can be used to make material exhibiting low heat release rate (HRR) when they undergo heat. We have developed novel approaches to characterize quantitatively the nanodispersion by solid state NMR and by TEM associated with image analysis and we have demonstrated that the dispersion at the nanoscale is essential to achieve the best performance. On the other hand, low flammability of nanocomposites is only achieved in terms of HRR but they fail in terms of UL-94 and limiting oxygen index (LOI). To overcome this problem, we have combined nanoparticles with traditional flame retardants (intumescents) or with plasma treatment. The nanofillers act as synergists and offer an exceptional way for making fire safe polymers.