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The direct chemical reactivity between phosphorus and nitrogen was induced under high-pressure and high-temperature conditions (9.1 GPa and 2000-2500 K), generated by a laser-heated diamond anvil cell and studied by synchrotron X-ray diffraction, Raman spectroscopy, and DFT calculations. α-P

High pressure reactivity of phosphorus and hydrogen is relevant to fundamental chemistry, energy conversion and storage, and materials science. Here we report the synthesis of (PH3)2H2, a crystalline van der Waals (vdW) compound (I4cm) made of PH3 and H2 molecules, in a Diamond Anvil Cell by direct catalyst-free high pressure (1.2 GPa) and high temperature (T ≲ 1000 K) chemical reaction of black phosphorus and liquid hydrogen, followed by room T compression above 3.5 GPa. Group 15 elements were previously not known to form H2-containing vdW compounds of their molecular hydrides. The observation of (PH3)2H2, identified by synchrotron X-ray diffraction and vibrational spectroscopy (FTIR, Raman), therefore represents the discovery of a previously missing tile, specifically corresponding to P for pnictogens, in the ability of non-metallic elements to form such compounds. Significant chemical implications encompass reactivity of the elements under extreme conditions, with the observation of the P analogue of the Haber-Bosch reaction for N, fundamental bond theory, and predicted high pressure superconductivity in P-H systems., Chemical elements at high pressure may behave more consistently with their periodic properties than they do at ambient conditions. The authors report the synthesis of PH3 from black phosphorous and hydrogen, and the crystallization of the van der Waals compound (PH3)2H2 which fills a gap in the chemistry of adjacent elements in the periodic table.

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.

International audience; Black phosphorus (bP) is a crystalline material which can be seen as an ordered stacking of two-dimensional layers, referred to as Phosphorene. The knowledge of the linear thermal expansion coefficients (LTEC) of bP is of great interest in the field of 2D materials for a better understanding of the anistropic thermal properties and exfoliation mechanism of this material. Despite several theoretical and experimental studies important uncertainties remain in the determination of the LTEC of bP. Here, we report accurate thermal expansion measurements along the three crystallographic axes using in-situ high temperature x-ray diffraction. From the progressive reduction of the diffracted intensities with temperature we monitored the loss of the crystal structure of bP across the investigated temperature range, evidencing two thermal expansion regimes at temperature below and above 706 K. Below 706 K, we observe a strong out-of-plane anisotropy, while at temperatures above 706 K a larger thermal expansion occurs along the a crystallographic direction. From our data and by taking advantage of ab-initio optimization, we propose a detailed anisotropic thermal expansion mechanism of bP, which leads to an inter- and intra-layer destabilization. An interpretation of it, based on the high T perturbation of the stabilizing sp orbital mixing effect, is provided, consistently with high pressure data.

Black phosphorus was studied by state-of-the-art synchrotron X-ray diffraction in a Diamond Anvil Cell during room temperature compression in the presence of He, H2, N2 and Daphne Oil 7474. The data demonstrate that the existence of the pseudo simple-cubic (p-sc) structure above 10.5 GPa is an intrinsic feature of P independent from the pressure transmitting medium. In the case of He, the pressure evolution of the lattice parameters and unit cell volume of P across the A17, A7 and p-sc structures was obtained and the corresponding EOS derived, providing a deeper insight on the recently reported p-sc structure. The results presented in this letter highlight the key role of the s-p orbital mixing in the formation and stabilization of the p-sc structure up to ~30 GPa, solving apparent contradictions emerging from previous literature and finally bringing order to the sequence of the high pressure A7 layered structure in group 15 elements.

The role of carbonaceous deposits (coke) formed in dehydrogenation catalysis has been extensively investigated over the last few decades mainly with respect to the deactivation of metal-based and metal-free heterogeneous catalysts. Although much less emphasized, coke deposits grown on selected metal oxides have also been described as active and selective phases for alkene dehydrogenation under an oxidative or non-oxidative atmosphere. This work describes the straightforward preparation of "coked" ?-AlO composites and their catalytic performance in the ethylbenzene (EB) direct dehydrogenation (DDH) to styrene (ST) under steam- and oxygen-free conditions. The study unveils the effective potentiality of a catalytic system already known to the scientific community but never employed for EB DDH under severe conditions, close to those commonly used in industrial plants (600 °C, 10 vol % EB/He, GHSV = 3000 h). Such a simple catalytic system has revealed a significant stability on long-term trials (>=150 h) and markedly high ST selectivity (>=97%) along with process rates (? up to 16.3 mmol g h) that are the highest claimed so far for related carbon systems at work in the process. Furthermore, the outlined performance of our composites in DDH is close to that claimed for classical iron-based industrial catalysts operating in the presence of a large amount of steam. ?-AlO precoking with an aliphatic C-source has shown additional beneficial effects on the ultimate ?-AlO@C performance in DDH. These findings pave the way for the development of cheap and durable dehydrogenation catalysts. They rewrite (in part at least) the role of coke in a challenging heterogeneous process while offering important hints to the comprehension of the reaction mechanism promoted by plain C-sites.

The crystalline A17 layered structure of Phosphorus, commonly indicated as black Phosphorus, was synthesized for the first time at high pressure by Bridgman back in 1914 [1] and is currently attracting a growing attention from chemists, physicists and materials scientists due to the appealing properties of its monolayer counterpart named Phosphorene [2]. Recently, high pressure studies have reported the observation of a pseudo simple cubic (p-sc) structure in the phase diagram of Phosphorus up to 30 GPa, significantly raising the pressure limit for the layered structures of P and opening new perspectives for their stabilization and functionalization [3-4]. On the other side, the experimental report of superconductivity in compressed PH 3 [5], with no structural characterization so far, has stimulated experimental and theoretical efforts to investigate the high pressure stability of different systems containing Phosphorus and Hydrogen, which can be responsible for such behavior in analogy with H 2 S [6,7]. In this study we investigated the chemical reactivity of black Phosphorus and molecular Hydrogen under high pressure and high temperature conditions, which were generated using a membrane Diamond Anvil Cell (DAC) in combination with laser heating. The sample was probed by means of synchrotron X-ray diffraction at ESRF-ID27 and by FTIR and Raman spectroscopy at LENS. The visual inspection of the sample after laser heating clearly showed the consumption of Phosphorus. Correspondingly, the analysis of the experimental XRD and spectroscopic data indicated the formation of different reaction products containing P-H bonds, particularly PH 3 , H-functionalized Phosphorus fragments and a solid product identified as a van der Waals compound made of PH 3 and H 2 , whose crystal structure was accurately determined from single crystal data. The identification of this compound, representing so far a missing piece, consistently fills a gap in the periodic table for Phosphorus, in agreement with analogous compounds reported in literature formed by the hydrides of Carbon (CH 4 ), Sulphur (H 2 S), Selenium (H 2 Se) and Iodine (HI) in the presence of H 2 [8-11]. Furthermore, the observation of this compound provides new experimental evidence for the formation of unexpected chemical species originating from the high pressure chemistry of Phosphorus and Hydrogen, possibly shedding new light on the high pressure superconductivity of Phosphorus-Hydrogen systems. Acknowledgments: Thanks are expressed to EC through the European Research Council (ERC) for funding the project PHOSFUN "Phosphorene functionalization: a new platform for advanced multifunctional materials" (Grant Agreement No. 670173) through an ERC Advanced Grant. References [1] P. W. Bridgman, J. Am. Chem. Soc. 1914, 36, 1344. [2] M. Peruzzini et al., Eur. J. Inorg. Chem. 2019, 1476. [3] D. Scelta et al., Angew. Chem. Int. Ed. 2017, 56, 14135. [4] D. Scelta et al., Chem. Commun. 2018, 54, 10554. [5] A. P. Drozdov et al., arXiv:1508.06224 (2015). [6] T. Bi et al., Angew. Chem. Int. Ed. 2017, 56, 10192. [7 M. Liu et al. J. Raman Spectrosc. 2018, 49, 721. [8] M. S. Somayazulu et al., Science 1996, 271, 1400. [9] T. A. Strobel et al. Phys. Rev. Lett. 2011, 107, 255503 .[10] E. J. Pace et al., J. Chem. Phys. 2017, 147, 184303. [11] Binns J. et al., Phys. Rev. B 2018, 97, 024111. Keywords: Phosphorus, Hydrogen, high pressure chemistry

In this paper, we describe the combination of two different synthetic approaches to carbon nanotube N-decoration/doping: the chemical functionalization with tailored N-pyridinic groups and the classical Chemical Vapor Deposition (CVD) technique. Accordingly, CVD-prepared N-doped CNMs (NMWs) and their N-decorated (chemically functionalized) counterparts (NMW@N1,2) have been prepared and used as metal-free electrocatalysts for the oxygen reduction reaction (ORR). It has been demonstrated that chemical functionalization occurs on the NMW surface sites responsible for their inherent electrochemical properties and “switches them off”. As a result, the ORR promoted by NMW@N1,2 is fully controlled by the appended N-heterocycles. A comparative analysis of N-functionalized samples and N-doped (CVD prepared) materials is used to foster the hypothesis of a unique N-configuration (N-pyridinic) responsible for the overall electrochemical performance in NMWs. In addition to that, original electrochemical insights unveiled during the study are discussed and the truly metal-free action of NMW in ORR catalysis is demonstrated.

High pressure chemistry: materials under extreme conditions During the last 20 years high pressure science has experienced a dramatic growth and nowadays encompasses a huge variety of research areas, spanning from biology and food processing to chemistry and physics of matter under extremes conditions. In this presentation, after a brief introduction about the generation of static high pressure in the GPa range and the effect of pressure on molecular systems, I will present a selection of significant studies, which highlight the importance of pressure not only to explore the fundamental chemical and physical properties of matter, but also to synthesize new advanced materials and gain insight about their structural and reactive properties. I will finally focus on our recent results about the mechanism of the high pressure A7 to sc phase transition in Phosphorus and the discovery of the pseudo-simple cubic (p-sc) structure, which have remarkable implications [1]. From a chemical point of view, the observation of the p-sc structure up to about 30 GPa significantly raises the pressure limit where the layered structures of P exist and reconciles the chemical and structural high pressure behavior of P with those of heavier pnictogens, finally bringing order to the sequence of the high pressure limit of the A7 layered structure in group 15 elements of the periodic table [2]. Moreover, the identification of the effects ruling the stability of the layered vs non-layered structure of P opens new perspectives for the synthesis, stabilization and functionalization of Phosphorene-based materials. As superconductivity is concerned, the identification of the p-sc structure provides new experimental evidence to explain the long-debated anomalous pressure evolution of Tc in P below 30 GPa. [1] D. Scelta, A. Baldassarre, M. Serrano-Ruiz, K. Dziubek, A. B. Cairns, M. Peruzzini, R. Bini, M. Ceppatelli, "Interlayer Bond Formation in Black Phosphorus at High Pressure", Angew. Chem. Int. Ed. 2017, 56, 14135-14140, DOI 10.1002/anie.201708368. [2] D. Scelta, A. Baldassarre, M. Serrano-Ruiz,a K. Dziubek, A. B. Cairns, M. Peruzzini, R. Bini and M. Ceppatelli "The p-sc structure in Phosphorus: bringing order to the high pressure phases of group 15 elements" Chem. Commun. 2018 (in press).

The recent synthesis of Phosphorene [1,2] and the theoretical predictions of a variety of related 2D allotropes [3] have raised a growing interest from the scientific community about the layered structures of Phosphorus. Indeed, black Phosphorus (bP, A17), formed by the ordered stacking of Phosphorene layers in a similar way as graphene is related to graphite, is actually the starting material for the synthesis of Phosphorene by exfoliation techniques. However, while the synthesis and stabilization of Phosphorene are still challenging tasks, its chemistry and functionalization represent frontier research topics. Within this perspective, pressure has been shown to be a very effective tool. Besides bP, another layered structure of P, rhombohedral A7, made by the stacking of blue Phosphorene layers, is indeed experimentally accessible by pressure. Remarkably, pressure has recently allowed to gain fundamental insight about the mechanism ruling the formation of chemical bonds between P layers, unveiling the existence of an intermediate p-sc structure between the layered rhombohedral A7 and the non-layered simple-cubic phases of P, significantly raising the pressure limit where the layers of P can be observed up to at least 30 GPa [4]. In this study we report the high pressure and high temperature chemistry of Phosphorus in the presence of N2 by means of state-of-the-art synchrotron X-ray diffraction (at ESRF-ID27), FTIR and Raman spectroscopy, using membrane Diamond Anvil Cell for the generation of static high pressure and laser heating for in situ generation of high temperature. Besides the N- functionalization of Phosphorene layers, this study is relevant to the substantially unexplored chemistry of the lowest Z pnictogens and to the synthesis of new PN compounds. Crystalline black Phosphorus was laser heated under different pressure and temperature conditions, corresponding to different crystalline structures of Phosphorus (A17, A7 and sc), above and below the melting line of N2. The results indicate a pressure dependent chemical reactivity, leading to different reaction products, according to the applied pressure. The low pressure data demonstrated the first direct synthesis of gamma-P3N5 from the elements, avoiding any precursor or byproduct [5]. Raman spectra and XRD patterns were acquired at high and ambient pressure, tracing the equation of state of the material, and providing new experimental input about the existence of the predicted delta- P3N5 phase [6-7]. References [1] Liu, H.; Neal, A. T.; Zhu, Z.; Luo, Z.; Xu, X.; Tománek, D.; Ye, P. D. Phosphorene: An Unexplored 2D Semiconductor with a High Hole Mobility, ACS Nano 2014, 8, 4033-4041. [2] Li, L.; Yu, Y.; Ye, G. J.; Ge, Q.; Ou, X.; Wu, H.; Feng, D.; Chen, X. H.; Zhang, Y. Black phosphorus field-effect transistors, Nat. Nanotechnol. 2014, 9, 372-377. [3] Woo Hyun Han, W.H. Sunghyun Kim, S.; Lee, I-H.; Chang, L.J. Prediction of Green Phosphorus with Tunable Direct Band Gap and High Mobility, J. Phys. Chem. Lett. 2017, 8, 4627-4632. [4] Scelta, D.; Baldassarre, A.; Serrano-Ruiz, M.; Dziubek, K.; Cairns, A. B.; Peruzzini, M.; Bini, R.; Ceppatelli, M. Interlayer Bond Formation in Black Phosphorus at High Pres- sure, Angew. Chem. Int. Ed. 2017, 56, 14135-14140. [5] Landskron, K.; Huppertz, H.; Senker, J. and Schnick, W. High-Pressure Synthesis of gamma- P3N5 at 11 GPa and 1500 °C in a Multianvil Assembly: A Binary Phosphorus (V) Nitride with a Three-Dimensional Network Structure from PN4 Tetrahedra and Tetragonal Pyramids Angew. Chem. Int. Ed. 2001, 40, 2643-2645. [6] Dong, J.; Kinkhabwala, A. A.; McMillan, P. F. , High-pressure polymorphism in phosphorus nitrides Physica Status Solidi B, 2004, 210, 2319-2325. [7] Kroll, P.; Schnick, W. A Density Functional Study of Phosphorus Nitride P3N5 : Refined Geometries, Properties, and Relative Stability of alpha-P3N5 and gamma-P3N5 and a Further Possible High-Pressure Phase delta-P3N5 with Kyanite-Type Structure Chem. Eur. J. 2002, 8, 3530- 3537.

A pressure induced lattice expansion of Graphite Oxide (GO) in presence of NH 3 was observed by X-ray diffraction during room temperature compression and decompression up to 7 GPa in a diamond anvil cell (DAC). A remarkable increase ( ∼ 11%) of the interlayer d-spacing of GO was observed between 0.2 and 1.1 GPa in the liquid phase of NH 3 , indicating the occurrence of molecular insertion between the GO layers. The expansion is reversible with the release of pressure, thus leading to a pressure induced breathing of the GO lattice. The presence of high density NH 3 between the GO layers opens new perspectives for N-doping and chemical functionalization of GO and for designing new advanced carbon based nanostructured 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.

A straightforward, energy- and atom-saving process to the production of tailored N-doped and catalytically active metal-free carbon nanostructures, has been set up. Our ex situ approach to the N-decoration of the carbon nanotube sidewalls contributes to elucidate the complex structure-reactivity relationship of N-doped carbon nanomaterials in oxygen reduction reactions, providing fundamental insights on the nature of the N-active sites as well as on the role of neighboring carbons.

Dissociation of ethanol by two-photon absorption of UVML laser emission centered at 350 nm was employed to trigger a chemical reaction at ambient temperature with red phosphorus for pressures ranging between 0.2 and 1.5 GPa. The reaction products, identified by infrared and Raman spectroscopy, indicate a quite selective reactivity ascribable to the two main dissociation channels involving the splitting of the O-H and C-O bonds of ethanol. The ethoxy radical, obtained through the splitting of the O-H bond, has been identified as the main responsible for the phosphorus reactivity, giving rise to triethylphosphate. The same dissociation channel is also responsible for the formation of a consistent amount of molecular hydrogen, phosphine, and diethyl ether, whereas ethane and ethylene, the latter observed only in traces, likely derive from the C-O dissociation. The reaction is accelerated by increasing pressure from 0.2 to 0.6 GPa but is not favored, as also observed in pure ethanol, by a further pressure increase. The reaction proceeds until ethanol is completely consumed, and further irradiation determines the decomposition of the products, especially of diethyl ether, leading to the formation of CO2, methane, and ethane.

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.

No abstract available.

High pressure chemical reactions of molecular systems are discussed considering the various factors that can affect the reactivity. These include steric hindrance and geometrical constraints in the confined environment of crystals at high pressure, changes of the free energy landscape with pressure, photoactivation by two-photon absorption, local and collective effects. A classification of the chemical reactions at high pressure is attempted on the basis of the prevailing factors.

It is shown that photoinduced reactions are observed at room temperature and pressure of few tenths of gigapascal in clathrate hydrates of CO and of model hydrocarbons under mild irradiation at 350 nm with power in the 50-610 mW range. The reactions are triggered by highly reactive OH radicals produced by two-photon excitation of the lowest electronic excited state of water having dissociative character. The formation of CO(2) is observed in all the reactions involving carbonaceous clathrate hydrates, and direct or indirect evidence for the formation of molecular hydrogen is obtained. The CO(2) produced in the reactions can be sequestered as a clathrate hydrate whose stability range seems to extend to room temperature at pressures of 0.5-0.6 GPa. Although the N(2) hydrate is stable up to 0.9 GPa under irradiation, a partial cleavage of the N-N triple bond is produced once the hydrate decomposes at 0.1 GPa.

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.

The pressure induced reactivity of carbon monoxide was investigated in a wide temperature range (100-400 K) completely avoiding any irradiation of the sample with visible or higher frequency light. FTIR spectroscopy was employed to monitor the reaction and infrared sensors for measuring the pressure. With this approach we have been able to separate the effects of the three variables (P, T and hnu) that establish the conditions for the occurrence of the chemical reaction. A new instability boundary, not affected by the photoactivation of the reaction, is provided. The reaction has been studied in three different crystal phases (epsilon, delta, and beta), but the small differences in the reaction products are ascribable to the temperature changes rather than to the crystalline arrangement. For T300 K the analysis of the IR spectra reveals the formation of an extended amorphous material formed, according to the vibrational assignment and to the kinetic data, by polycarbonyl linear chains containing a large amount of anhydride groups. For Tor=300 K the formation of carbon dioxide and epoxy rings, and the simultaneous decrease of carbonyl species, let suppose a decarboxylation of the extended solid product. Once exposed to the atmosphere, the reaction product readily and irreversibly reacts with water giving rise to carboxylic groups.

The advantages of the use of optical spectroscopy methods (infrared and Raman spectroscopy, electronic spectroscopy) in the study of high pressure transformation and chemical reactions are illustrated considering several examples. In particular, the efficiency of the spectroscopic methods in the analysis of phase transitions at high pressure, of pressure induced changes of the electronic structure and of the elucidation of the reaction mechanisms at very high pressures are considered.

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.

A study was conducted to demonstrate the synthesis of high pressure synthesis of all-transoid polycarbonyl [-(C=O)]n in a zeolite. The study also demonstrated the feasibility of inducing the self-assembly of dense CO in the spatially subnano-confined region of the channels of an electrically neutral, non-catalytic, hydrophobic, and all SiO2 zeolite silicalite. It was observed that the insertion of simple guest molecules, such as Ar and CO2 in the channels of this zeolite deactivated the pressure induced amorphization of the framework up to at least 25 GPa.

The structural transformations occurring in Ge2Sb2Te5 films heated at temperature up to 400 °C, and under hydrostatic pressure up to 12 GPa, have been investigated through in-situ X ray diffraction measurements. The adopted experimental conditions are close to those experienced by the phase change material during the SET (crystallization)/RESET (amorphization) processes in a nonvolatile memory device. The compression enhances the thermal stability of the amorphous phase, which remains stable up to 180 °C at 8 GPa and to 230 °C at 12 GPa. The structure of the crystalline phases is also modified, with the formation of a CsCl-type structure instead of rock-salt and of a GeS-type structure at the temperature at which usually the trigonal stable phase is formed. Overall, the stability of the stable phase appears to be more affected by the compression. We argue that the presence of weak bonds associated to the van der Waals gaps is a determining factor for the observed reduced stability.

The role of light absorption in triggering the high-pressure reaction of solid furane is investigated. When the sample is irradiated with the 458.0-nm line of an Ar+ ion laser the reaction is found to occur just above 3 GPa, well below the pressure value (10 GPa) where it takes place without irradiation. The pressure threshold of the transformation increases as the excitation line is shifted to the red. The analysis of the pressure evolution of the UV-VIS absorption spectrum allows us to identify the injection mechanism as a two-photon absorption process to the lowest excited states of furane. The aromatic ring opening shows, in this case, additional reaction paths with respect to the purely pressure induced reaction, as attested by the presence of CO2 and by the larger amount of carbonyl groups found in the recovered product. These results suggest the ring opening mechanism to be mainly controlled by the relative molecular orientation both in the disordered phase IV and in the ordered phase III.

FTIR spectroscopy was applied to the study of the high-pressure reactivity of solid butadiene. The chemical transformation from the ordered phase I was observed to occur only above 270 K. The existence of a threshold temperature for the reaction reveals the central role of the lattice phonons in the activation of the transformation. Below 4.0 GPa only dimerization to 4-vinylcyclohexene occurs, while above this pressure an increasing amount of polymer forms with rising pressure. Room temperature kinetic studies have been performed at different pressures, from 2.1 up to 6.6 GPa, and the sign of the activation volume for the dimerization has been obtained. The dimerization reaction is found to follow a first-order mechanism. A reaction pathway for this process is proposed where the internal rearrangement of a diradical intermediate specie is identified as the rate limiting step. An acceleration of the dimerization process is observed above 4.0 GPa and is ascribed to the simultaneous polymer formation. This effect causes the laser assisted reaction, where a large amount of polymer is produced at any pressure, to be not as selective on polymerization as it is in the liquid phase, since also the dimerization rate is enhanced.

The behavior of crystalline furan has been investigated, at room temperature, along the 0–47–0 GPa pressure cycle by using IR and Raman spectroscopy. These data, joint to high pressure low temperature IR data, allow the identification of two solid phases in the 1.2–12 GPa pressure range: the low-pressure orientationally disordered phase IV and the high-pressure ordered phase III. Above 10–12 GPa solid furan starts to chemically transform. The threshold pressure for the transformation is much lower than in benzene, as expected according to the minor stability of the heteroaromatic ring. The reaction proceeds continuously along the compression path, but it becomes complete only with releasing pressure, and a yellow–brownish sample is recovered. This compound was identified as an amorphous hydrogenated carbon (a-C:H) containing alkylpolyether type segments, alcoholic functions, and C=O bonds. The presence of these new chemical species attests to the opening of the original furan rings and to the transfer of hydrogen atoms. The reaction seems to be very similar to that induced in crystalline benzene. This comparison indicates a general behavior for the reactivity under ultrahigh pressures of the whole class of aromatic compounds.

In the present work the first spectroscopic data concerning solid butadiene are presented. FTIR and Raman spectra of solid trans -1,3 butadiene in the ordered phase I were recorded at atmospheric pressure down to 12 K. The FTIR technique was used to characterize the phase diagram of butadiene in the 0–7 GPa and 150–300 K pressure–temperature range. Besides phase I another solid phase (phase II), orientationally disordered, was found to be stable at pressures above 0.5 GPa between the liquid and the ordered phase I. A monoclinic C 2h 5 crystal structure with two molecules per cell sitting on C i sites is proposed for phase I.

Polycrystalline all–trans retinal (ATR) has been excited at 647.1 nm under pressure up to 9 GPa at room temperature and the resulting Raman spectrum has been measured. The large majority of Raman bands in the 700–1700 cm−1 range have positive pressure coefficients, i.e. bonds stiffen upon compression. The Raman spectrum is recovered after the compression–decompression cycle indicating that the molecular unit does not undergo an irreversible transformation under our experimental conditions. Model density functional (DF) calculations with the B3-LYP exchange-correlation functional and the 6-31G* basis set have been performed on 1-cis,3-trans,5-trans,7-trans,9-trans,1,5,9-trimethyldecapentaenal (TMDPL) mimicking the polyenic moiety of ATR. By shortening the single and double CC bonds of TMDPL up to 0.0015 A it was possible to fit the frequency dependence on pressure of the most intense polyenic bands with single and double bond compressibilities ≈0.00292 and 0.00117 A/GPa, respectively. The trans → cis isomerization in the crystal state under pressure and in the presence of the 647.1 nm excitation light is suggested by the Raman spectrum in the fingerprint region. A simplified model is proposed for the occurrence of this process in the crystal phase.

Conducting polymers are one of the most promising classes of materials for enabling technologies such as solar energy conversion, organic electronics, and opto-electronics. The text-book conducting polymer is polyacetylene, which is difficult to synthesize in the all-conjugated form and also reacts with atmospheric moisture. Zeolites, widely used in diverse fields, could provide the ideal microporous framework capable of driving the ordered polymerization of acetylene. Also, the embedded polymer would be chemically protected by the zeolite, resulting in a unique organic/inorganic, conducting nanocomposite. We polymerized acetylene in the channels of a noncatalytic, pure SiO2 zeolite, silicalite in a diamond anvil cell, using only high pressure (~4 GPa) as the driving force. A unique nanocomposite was obtained and recovered at ambient pressure, made of conjugated chains embedded in the silicalite as determined by combining different techniques: IR spectroscopy, Raman spectroscopy and microscopy, and X-ray diffraction. We thus made the first step toward the synthesis of a new generation of conducting polymers embedded in nanostructured hosts and also added to the development of mechanochemistry in highly confined systems.

This report presents the influence of the morphology on the pressure-induced reactivity of the doped (PANI-ES) and dedoped (PANI-EB) forms of polyaniline using Raman and FTIR techniques. Our PANI-EB FTIR spectroscopy data showed an intensity exchange among characteristic bands of the quinoid and benzoic segments above 9 GPa, suggesting a specific coupling reaction between adjacent quinoid rings. The reaction kinetic was followed, and the results showed a dependence of the rate constant with pressure, as well as the activation volume, presented an inversion from negative to positive at 13 GPa, suggesting that steric factors have a role in the reactivity of the species. Raman spectra of PANI-ES showed a broadening and a blue shift of the bands as the pressure increases preceding the almost complete amorphization of the polymer; after decompression, some minor spectral changes were observed, suggesting the occurrence of the dedoping and cross-linking reactions in less extension than PANI-EB.

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.

The polymerization of solid acetylene under pressure has been studied by Fourier transform infrared (FTIR) spectroscopy. Controlled laser irradiation cycles and the employment of infrared sensors to measure the sample pressure, allowed to separate the photochemical and the pressure effect on the injection and on the evolution of the reaction. The careful assignment of all the spectral features and analysis of their relative intensities and frequencies gave evidence to the specific effect of pressure and laser irradiation on the reaction products. Pressure induces an ordered growth of trans-polyenic species, while irradiation produces the opening of the double bonds and a consequent branching of the chains. Constant pressure measurements allowed to obtain precise information on the kinetics of the reaction. A monodimensional growth geometry, involving the molecules on the bc plane, agrees with the parameters extracted by the kinetic curves. Comparison between experiments at different temperatures suggests ...

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.

Organic functionalization of carbon nanotube sidewalls is a tool of primary importance in material science and nanotechnology, equally from a fundamental and an applicative point of view. (1, 2) Here, an efficient and versa- tile approach for the organic/organo- metallic functionalization of single- walled carbon nanotubes (SWCNTs) capable of imparting multimodality to these fundamental nanostructures, is described. Our strategy takes advant- age of well-established Cu-mediated acetylene-azide coupling (CuAAC) re- actions applied to phenylazido-func- tionalized SWCNTs for their conven- ient homo-/heterodecoration with a number of organic/organometallic frameworks, or mixtures thereof, bear- ing terminal acetylene pendant arms. Phenylazido-decorated SWCNTs were prepared by chemoselective arylation of the CNT sidewalls with diazonium salts under mild conditions, and subse- quently used for the copper-mediated cycloaddition protocol in the presence of terminal acetylenes. The latter reac- tion was performed in one step by using either single acetylene derivatives or equimolar mixtures of terminal al- kynes bearing either similar functional groups (masked with orthogonally cleavable protecting groups) or easily distinguishable functionalities (on the basis of complementary analytical/spec- troscopic techniques). All materials and intermediates were characterized with respect to their most relevant as- pects/properties by TEM microscopy, thermogravimetric analysis coupled with MS analysis of volatiles (TG-MS), elemental analysis, cyclic voltammetry (CV), Raman and UV/Vis spectrosco- py. The functional loading and related chemical grafting of both primary amino- and ferrocene-decorated SWCNTs were spectroscopically (UV/ Vis, Kaiser test) and electrochemically (CV) determined, respectively.

The room-temperature reactivity of liquid methanol induced by two- photon absorption of near UV photons (350 nm) was studied as a function of pressure. Different chemical reactions were triggered by the radical species produced through the population of the lowest electronic excited singlet state because of its dissociative character. Experiments were performed at room temperature between 0.1 and 1.8 GPa on CH3OH and between 0.2 and 1.5 GPa on CD3OH. Different irradiation cycles were performed at constant pressure conditions, and FTIR and Raman spectra were measured to monitor the reaction evolution. Methoxymethanol and methylformate were the main products and the only ones detected in all the experiments. Ethylene glycol formed only at low pressure (0.2-0.3 GPa), whereas small amounts of methane, water, and unsaturated (C=C) species were also detected independently of the reaction pressure. Only dissociation along the O-H and C-O coordinates was relevant in the investigated pressure range. Ethylene glycol, methoxymethanol, and methylformate derive from the dissociation channel involving the O-H bond cleavage, whereas methane and unsaturated species come from the dissociation along the C-O bond. The comparison of the results obtained for the two isotopomers at the different investigated pressures allowed the identification of three different reactive paths that, starting from the methoxy radical, lead to the formation of the main products. The important effect of pressure on the reaction evolution could suggest a modification of the potential energy surface of the lowest electronic excited state along the O-H coordinate on increasing pressure.

Syntheses based on physical methods, such as pressure and light, are extremely attractive to prepare novel materials from pure molecular systems in condensed phases. The structural and electronic modifications induced by selective optical excitation can trigger unexpected chemical reactions by exploiting the high density conditions realized at high pressure. The identification of the microscopic mechanisms regulating this reactivity, mandatory to design synthetic environments appealing for practical applications, requires a careful characterization of both structural and electronic properties as a function of pressure. Here, we report a spectroscopic study, by FTIR and Raman techniques, of the ambient temperature photoinduced reactivity of liquid C(2)H(5)OD up to 1 GPa. The results have been interpreted by comparison with those relative to the fully hydrogenated isotopomer. The dissociation along the O-H (D) coordinate is the primary reactive channel, but the different reactivity of the two isotopomers with rising pressure highlights a dramatic pressure effect on the energy surface of the first electronic excited state. Dissociation along the O-H (D) coordinate becomes the reaction rate-limiting step due to an increase with pressure of the binding character along this coordinate.

The ambient temperature photoinduced reactivity of mixtures containing water and some of the simplest model hydrocarbons has been studied in a diamond anvil cell below 1 GPa. The near-UV 350 nm emission of an Ar ion laser has been employed to photodissociate water molecules through two-photon absorption processes. The hydroxyl radicals generated through this process are able to trigger a chemical reaction in the mixtures containing ethane and acetylene, which are otherwise stable under the same P-T-hnu conditions, whereas the contribution of water has no effect or is very limited in the case of the ethylene and propene mixtures, respectively. The reaction evolution and the reaction products were characterized by using FTIR spectroscopy. The formation of fluorescent products limits or prevents, as in the case of acetylene, the characterization by Raman spectroscopy. Particularly relevant is the in situ efficient sequestration of the CO(2) formed during the reaction, through the formation of a clathrate hydrate, in the mixtures where water is largely in excess.

High-pressure methods have been demonstrated to be efficient in providing new routes for the synthesis of materials of technological interest. In several molecular compounds, the drastic pressure conditions required for spontaneous transformations have been lowered to the kilobar range by photoactivation of the reactions. At these pressures, the syntheses are accessible to large-volume applications and are of interest to bioscience, space, and environmental chemistry. Here, we show that the short-lived hydroxyl radicals, produced in the photodissociation of water molecules by near-UV radiation at room temperature and pressures of a few tenths of a gigapascal (GPa), can be successfully used to trigger chemical reactions in mixtures of water with carbon monoxide or nitrogen. The detection of molecular hydrogen among the reaction products is of particular relevance. Besides the implications in fundamental chemistry, the mild pressure and irradiation conditions, the efficiency of the process, and the nature of the reactant and product molecules suggest applications in synthesis.

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.