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A comparison between the high-pressure (0.8 GPa) photo-induced reactivity of black and red phosphorus at ambient temperature in the presence of ammonia has been conducted in Diamond Anvil Cells (DAC), using spectroscopy (IR and Raman) and X-ray diffraction (XRD). Reactivity has been triggered exploiting the two-photon absorption of near-UV radiation by ammonia. The infrared characterization showed a very complex reactivity in the case of red phosphorus, proceeding to a much more extent with respect to the black allotrope. Furthermore, Raman spectra showed the formation of molecular hydrogen and phosphine besides of three different solid products. Whereas one of them is air sensitive, the other two are recoverable at ambient conditions. IR, Raman and XRD data for the obtained products have been compared to those acquired on known HxPyNz compounds: for one of the two stable products, a fair matching was found with the XRD pattern and the IR spectrum of P3N3(NH2)6 ·(NH3)0.5, whereas for the other one only the functional groups actually involved in the structure could be evinced from accurate Raman mapping of the sample, with no further information about composition or stoichiometry. High density conditions in combination with near-UV laser irradiation were thus proved to be effective in the formation of two stable reaction products featuring new P-N functionalities, both recoverable at ambient pressure. For the first time, a cyclic triphosphazene has been synthesized through the reaction of red phosphorus and ammonia triggered by UV light under moderate high pressure conditions, possibly opening new perspectives about this topic.

Chemical reactivity between As and N2 , leading to the synthesis of crystalline arsenic nitride, is here reported under high pressure and high temperature conditions generated by laser heating in a Diamond Anvil Cell. Single crystal synchrotron X-ray diffraction at different pressures between 30 and 40 GPa provides evidence for the synthesis of a covalent compound of AsN stoichiometry, crystallizing in a cubic P213 space group, in which each of the two elements is single-bonded to three atoms of the other and hosts an electron lone pair, in a tetrahedral anisotropic coordination. The identification of characteristic structural motifs highlights the key role played by the directional repulsive interactions between non-bonding electron lone pairs in the formation of the AsN structure. Additional data indicate the existence of AsN at room temperature from 9.8 up to 50 GPa. Implications concern fundamental aspects of pnictogens chemistry and the synthesis of innovative advanced materials.

Black phosphorus was compressed at room temperature across the A17, A7 and simple‐cubic phases up to 30 GPa, using a diamond anvil cell and He as pressure transmitting medium. Synchrotron X‐ray diffraction showed the persistence of two previously unreported peaks related to the A7 structure in the pressure range of the simple‐cubic phase. The Rietveld refinement of the data demonstrates the occurrence of a two‐step mechanism for the A7 to simple‐cubic phase transition, indicating the existence of an intermediate pseudo simple‐cubic structure. From a chemical point of view this study represents a deep insight on the mechanism of interlayer bond formation during the transformation from the layered A7 to the non‐layered simple‐cubic phase of phosphorus, opening new perspectives for the design, synthesis and stabilization of phosphorene‐based systems. As superconductivity is concerned, a new experimental evidence to explain the anomalous pressure behavior of Tc in phosphorus below 30 GPa is provided.

The high pressure structural and reactive beahvior of graphene oxide (GO) in the presence of Ar, N2, and NH3 was studied in diamond anvil cells (DAC) by X-ray diffraction (XRD) and vibrational spectroscopy (FTIR and Raman), with the purpose of investigating the use of pressure for N-doping and functionalization of GO in high-density conditions. The pressure evolution of the interlayer d-spacing of GO during room temperature compression and decompression indicates the pressure-induced insertion of the selected systems between the GO layers and the stability of the GO layered structure at high pressure. Thermal and photoinduced reactivity was studied in GO with N2 and in GO with NH3 in different pressure conditions. The comparison of the infrared spectra of the recovered samples at ambient conditions with respect to the starting GO provides evidence for the occurrence of chemical reactivity of N2 and NH3 with GO, leading to N incorporation and GO functionalization, as also confirmed by the Raman spectra. The observed reactivity opens new perspectives for the high-pressure chemistry of GO and carbon-based nanostructured systems.

Recently, simple carbon based polymers have been synthesized at high pressures in silicalite, a pure SiO2 zeolite with a 3D system of mutually interconnected microchannels. These protocols permitted otherwise unstable polymers to be stabilized and protected from the atmosphere and to obtain an entirely novel class of nanocomposites with modified physical properties. In these 3-D systems, channel interconnection may prevent ideal, isolated polymer chains to be obtained. In this work, the :high pressure (5-10 GPa) synthesis of two archetypal, linear polymers polyacetylene (PA) and polycarbonyl (pCO) in the 1D channel system of the pure SiO2 zeolite ZSM-22 (TON) has been performed. The two resulting nano composites PA/TON and pCO/TON are organic/inorganic composite materials, which are good candidates as highly directional semiconductors and high energy density materials, respectively. The synthesis was performed in diamond anvil cells, starting from dense C2H2 and CO, confined in ZSM-22, and the nanocomposites were recovered at ambient conditions. The monomer polymerization was proven by IR spectroscopy and synchrotron X-ray diffraction measurements. DFT calculations were performed in order to obtain insight about the configurations of the 1D embedded polymers.

The spontaneous polymerization of fluid ethylene under high temperature and pressure conditions has been characterized by using FTIR absorption spectroscopy. The fluid has been isobarically heated at pressures ranging between 0.4 and 1.5 GPa by means of a resistively heated membrane diamond anvil cell. Besides tracing the instability boundary for spontaneous polymerization in the fluid, we have also measured the reaction kinetics at 1.5 GPa and temperatures ranging between 340 and 423 K. From the rate constants the activation energy of the overall reaction could be computed, information that joined to the molecularity of the initiation step provides some insight about the reaction mechanism. The polymers recovered from the different reactions have been characterized by FTIR, Raman, and X-ray diffraction revealing in all the cases a crystalline material of astonishing quality, likely related to the growth of the polymer in the hot fluid monomer.

An efficient loading technique has been developed for flammable, toxic, or explosive gases which can be condensed at liquid nitrogen temperature and ambient pressure in membrane diamond anvil cells (DACs). This cryogenic technique consists in a deposition of small quantities of the desired gas directly into the sample chamber. The deposition is performed using a capillary that reaches the space between the diamond anvils. The DAC is kept under inert gas overpressure during the whole process, in order to avoid contamination from atmospheric O2, CO2, and H2O. This technique provides significant advantages over standard cryo-loading and gas-loading when the condensation of dangerous samples at liquid nitrogen temperature raises safety concerns because it allows dealing with minimum quantities of condensed gases. The whole procedure is particularly fast and efficient. The "spray-loading" has been successfully used in our laboratory to load several samples including acetylene, ammonia, ethylene, and carbon dioxide/water or red phosphorus/NH3 mixtures.

This article is part of an extended study concerning the reactivity of acetylenic systems at high pressure and aims to the investigation of the high pressure synthesis and stabilization of polyacetylenic chains. The data for diphenylacetylene (DPA) are interpreted by establishing a comparison with the results obtained for acetylene, phenylacetylene, DPA and benzene. The room temperature high-pressure reaction of DPA was studied by means of Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy using a membrane diamond anvil cell (MDAC). The appearance of the sp3 C–H stretching absorption in the Infrared (IR) spectrum at about 9 GPa, indicates the formation of chemical bonds among the aromatic rings belonging to different DPA molecules. For higher pressures, the Raman data indicate the involvement of the internal C≡C moiety in the chemical transformation. Therefore, due to the steric hindrance of the phenyl rings, the pressure threshold for the reactivity of the two molecular fragments appea...

The high-pressure reactivity of isoprene has been studied at room temperature up to 2.6 GPa by using the diamond anvil cell technique in combination with Fourier transform infrared spectroscopy. Both dimerization and polymerization reactions take place above 1.1 GPa. At this pressure, the two processes are well separated in time, the dimerization being the only one occurring in the first 150 h. Both processes simultaneously occur as the pressure increases. The reaction product is composed of a volatile fraction, identified as sylvestrene, and a transparent rubberlike solid formed by cis-1,4- and 3,4-polyisoprene. The activation volume of the dimerization reaction has been obtained from the kinetic data. The photoinduced reaction, studied at room temperature for two different pressures, takes place through a two-photon absorption process, and the threshold pressure is lowered to 0.5 GPa. At this pressure, both the dimerization and polymerization processes occur, but the dimerization is not as selective as in the purely pressure-induced reaction. 4-Ethenyl-2,4-dimethylcyclohexene is obtained in addition to sylvestrene. By increasing the pressure, the photoinduced reaction becomes more selective, and the monomer is quantitatively transformed into the same polymer obtained in the purely pressure-induced reaction.

The characterization of pressure induced structural and chemical transformations employing the Diamond Anvil Cell (DAC) technique often requires a high spatial resolution. This is due to the small sample dimensions when the compression reaches the megabar range, or when heterogeneous materials are obtained in pressure induced chemical reactions. The characterization of these samples can be performed by using synchrotron light based techniques, which can provide optical or X-ray spots of few microns, whereas laboratory experiments are limited to Raman spectroscopy. Here we describe a cutting-edge Raman system with a transverse spatial resolution of 1-3 ?m dedicated to the characterization of samples compressed in DACs. A few examples of the application of this technique to characterize different heterogeneous materials before and after high-pressure chemical reactions are reported to enlighten the performances of the system

The combined effect of high pressure and electronic photo-excitation has been proven to be very efficient in activating extremely selective polymerisations of small unsaturated hydrocarbons in diamond anvil cells (DAC). Here we report an ambient temperature, large volume synthesis of high density polyethylene based only on high pressure (0.4-0.5 GPa) and photo-excitation (~350 nm), without any solvent, catalyst or radical initiator. The reaction conditions are accessible to the current industrial technology and the laboratory scale pilot reactor can be scaled up to much larger dimensions for practical applications. FTIR and Raman spectroscopy, and X-ray diffraction, indicate that the synthesised material is of comparable quality with respect to the outstanding crystalline material obtained in the DAC. The polydispersity index is comparable to that of IV generation Ziegler-Natta catalysts. Moreover the crystalline quality of the synthesised material can be further enhanced by a thermal annealing at 373 K and ambient pressure. High density polyethylene is synthesised at ambient temperature using only pressure and near-UV photons, without any solvent, catalyst or radical initiator. The reaction conditions are accessible to the current industrial technology and the dimensions of the laboratory scale pilot reactor can be scaled up for practical applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A high-pressure job: Under high-pressure conditions, within a diamond anvil cell, irradiation of red phosphorus (see scheme, orange) and water was found to lead to a reaction that gives H2, PH3, H3PO2, H3PO4, and H3PO4 (H gray, O red, P orange). This reaction can be easily monitored using Raman spectroscopy and presents an interesting method for H2 generation.

The phase diagram of propene has been investigated at high pressure by using the diamond anvil cell technique and Fourier transform infrared spectroscopy. The pressure conditions necessary to induce a spontaneous reaction of the sample have been found at different temperatures, allowing the stability boundary of propene to be drawn. The reaction is diffusion controlled and seems to occur only in the fluid phase, implying a slope inversion of the stability boundary at about 250 K. The product of the reaction is a mixture of linear oligomers independently of the P-T conditions. The activation volume and energy of the process have been obtained from the kinetic data. Also the activation of the reaction by laser absorption has been carefully studied. A high proton mobility has been identified as the likely reason that limits the lengthening of the chain up to six to eight monomeric units preventing the polymer formation.