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1.
Angew Chem Int Ed Engl ; 63(7): e202318214, 2024 Feb 12.
Artículo en Inglés | MEDLINE | ID: mdl-38100520

RESUMEN

The elements hydrogen, carbon, and nitrogen are among the most abundant in the solar system. Still, little is known about the ternary compounds these elements can form under the high-pressure and high-temperature conditions found in the outer planets' interiors. These materials are also of significant research interest since they are predicted to feature many desirable properties such as high thermal conductivity and hardness due to strong covalent bonding networks. In this study, the high-pressure high-temperature reaction behavior of malononitrile H2 C(CN)2 , dicyandiamide (H2 N)2 C=NCN, and melamine (C3 N3 )(NH2 )3 was investigated in laser-heated diamond anvil cells. Two previously unknown compounds, namely α-C(NH)2 and ß-C(NH)2 , have been synthesized and found to have fully sp3 -hybridized carbon atoms. α-C(NH)2 crystallizes in a distorted ß-cristobalite structure, while ß-C(NH)2 is built from previously unknown imide-bridged 2,4,6,8,9,10-hexaazaadamantane units, which form two independent interpenetrating diamond-like networks. Their stability domains and compressibility were studied, for which supporting density functional theory calculations were performed.

2.
Chemistry ; 29(43): e202301098, 2023 Aug 01.
Artículo en Inglés | MEDLINE | ID: mdl-37129208

RESUMEN

Two new Dion-Jacobson layered perovskite polymorphs of the known oxyfluoride compound KWO3 F are reported. A high-pressure modification was synthesized using a multianvil setup and subsequently transformed into a high-temperature phase at ∼311 °C. The crystal structures of both polymorphs were determined by use of single-crystal X-ray diffraction and are described in detail herein. Differential thermal analyses and thermogravimetric analyses were carried out to further investigate the phase transition characteristics. Bond valence (BV) and charge distribution (CHARDI) calculations confirm the occupancy of mixed O|F anion positions, and Rietveld refinements as well as MAPLE calculations support the structure models.

3.
Chemistry ; 28(36): e202200760, 2022 Jun 27.
Artículo en Inglés | MEDLINE | ID: mdl-35446988

RESUMEN

The oxonitridosilicate La7 Sr[Si10 N19 O3 ] : Eu2+ and its substitutional variants RE8-x AEx [Si10 N20-x O2+x ] : Eu2+ with RE=La, Ce; AE=Ca, Sr, Ba and 0≤x≤2 were synthesized starting from REN, SrN/Ca3 N2 /Ba2 N, SiO2 , amorphous Si3 N4 and Eu2 O3 as doping agent at 1600 °C in a radiofrequency furnace. The crystal structure of La7 Sr[Si10 N19 O3 ] was solved and refined based on single-crystal X-ray diffraction data. La7 Sr[Si10 N19 O3 ] crystallizes in the orthorhombic space group Pmn21 (no. 31). The crystal structures of the isotypic compounds RE8-x AEx [Si10 N20-x O2+x ] were confirmed by Rietveld refinements based on powder X-ray diffraction data using the single-crystal data of La7 Sr[Si10 N19 O3 ] as starting point. Crystal structure elucidation reveals a 3D network of vertex sharing SiN4 and SiN2 (N1/2-x/4 O1/2+x/4 )2 (0≤x≤2) tetrahedra. When excited with UV to blue light, La7 Sr[Si10 N19 O3 ] : Eu2+ shows amber luminescence with λem =612 nm and fwhm=84 nm/2194 cm-1 , which makes it interesting for application in amber phosphor-converted light emitting diodes.

4.
Chemistry ; 28(4): e202104007, 2022 Jan 19.
Artículo en Inglés | MEDLINE | ID: mdl-34846075

RESUMEN

The nitridosilicate CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) was synthesized by carbothermal reduction and nitridation starting from CaH2 , Lu2 O3 , graphite and amorphous Si3 N4 at 1550 °C in a radiofrequency furnace. CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) crystallizes isotypically to many previously known MII MIII Si4 N7 compounds in the space group P63 mc, as was confirmed by Rietveld refinement based on powder X-ray diffraction data. Incorporation of carbon into the crystal structure as a result of the carbothermal synthesis route was confirmed by 13 C and 29 Si MAS NMR spectroscopy. For the first time in the MII MIII Si4 N7 compound class, complementary EDX measurements suggest that simultaneous incorporation of oxygen compensates for the negative charge excess induced by carbon, resulting in an adjusted sum formula, CaLu[Si4 N7-2x Cx Ox ] (x≈0.3). When excited with UV-to-blue light, CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) shows an emission maximum in the blue spectral region (λem =484 nm; fwhm=4531 cm-1 ) upon doping with Ce3+ , whereas Eu2+ -doped CaLu[Si4 N7-2x Cx Ox ] (x≈0.3) exhibits a yellow-green emission (λem =546 nm; fwhm=3999 cm-1 ).


Asunto(s)
Nitrógeno , Oxígeno , Carbono , Luz , Difracción de Rayos X
5.
Chemistry ; 27(45): 11701-11706, 2021 Aug 11.
Artículo en Inglés | MEDLINE | ID: mdl-34111319

RESUMEN

In order to expand the field of alkali lithosilicates, a new representative of the substance class with a previously unknown structure type was found based on solid-state synthesis. The novel compound with the sum formula Rb[Li5 Si2 O7 ] crystallizes in the orthorhombic space group Pbcm (no. 57) with a=7.6269(3), b=9.5415(4), and c=9.4095(3) Šby means of single-crystal X-ray diffraction. The structure consists of a highly condensed lithosilicate framework, built up of corner- and edge-linked [LiO4 ]-tetrahedra and [Si2 O7 ]-units, and the rubidium ions aligned in channels. Suitable crystals of the material were obtained using sealed tantalum ampoules as reaction tube at a temperature of 750 °C. The new compound was further characterized via powder diffraction, Rietveld analysis, and EDX measurements. At first glance, Eu2+ -doped Rb[Li5 Si2 O7 ] reveals an intense green luminescence. In-depth crystal analysis shows that a core-shell formation is present even for apparently high quality single-crystals. As a minority phase, the known green phosphor RbLi[Li3 SiO4 ]2 :Eu2+ is the origin of the luminescence, representing a tiny core inside of the particles surrounded by a large matrix of transparent Rb[Li5 Si2 O7 ] dominating the single-crystal diffraction pattern.

6.
Chemistry ; 27(50): 12835-12844, 2021 Sep 06.
Artículo en Inglés | MEDLINE | ID: mdl-34240752

RESUMEN

Single-crystalline domains in intergrown microcrystalline material of the new compounds Ba22.5+x La55-x [Si129 N240-x Ox ]O3 :Ce3+ and Ba25.5+x La77-x [Si170 N312-x O9+x ]O4 :Ce3+ were identified by transmission electron microscopy (TEM). Precise diffraction data from these domains were collected with microfocused synchrotron radiation so that crystal structure elucidation of the complex disordered networks became possible. They are composed of two different interconnected slabs of which one is similar in both compounds, which explains their notorious intergrowth. The distribution of Ba and La is indicated by the analysis of bond-valence sums and by comparison with isostructural Sr28.5+x La75-x [Si170 N312-x O9+x ]O4 . Ce3+ doping leads to yellow luminescence. This is a showcase that highlights the discovery and accurate characterization of new compounds relevant for luminescence applications from heterogeneous microcrystalline samples by exploiting the capability of the combination of TEM and diffraction using the latest focusing techniques for synchrotron radiation.

7.
Chemistry ; 26(32): 7292-7298, 2020 Jun 05.
Artículo en Inglés | MEDLINE | ID: mdl-32267576

RESUMEN

The nitridophosphates AEP8 N14 (AE=Ca, Sr, Ba) were synthesized at 4-5 GPa and 1050-1150 °C applying a 1000 t press with multianvil apparatus, following the azide route. The crystal structures of CaP8 N14 and SrP8 N14 are isotypic. The space group Cmcm was confirmed by powder X-ray diffraction. The structure of BaP8 N14 (space group Amm2) was elucidated by a combination of transmission electron microscopy and diffraction of microfocused synchrotron radiation. Phase purity was confirmed by Rietveld refinement. IR spectra are consistent with the structure models and the chemical compositions were confirmed by X-ray spectroscopy. Luminescence properties of Eu2+ -doped samples were investigated upon excitation with UV to blue light. CaP8 N14 (λem =470 nm; fwhm=1380 cm-1 ) and SrP8 N14 (λem =440 nm; fwhm=1350 cm-1 ) can be classified as the first ultra-narrow-band blue-emitting Eu2+ -doped nitridophosphates. BaP8 N14 shows a notably broader blue emission (λem =417/457 nm; fwhm=2075/3550 cm-1 ).

8.
Chemistry ; 26(22): 5010-5016, 2020 Apr 16.
Artículo en Inglés | MEDLINE | ID: mdl-31944443

RESUMEN

Barium imidonitridophosphate BaP6 N10 NH was synthesized at 5 GPa and 1000 °C with a high-pressure high-temperature approach using the multianvil technique. Ba(N3 )2 , P3 N5 and NH4 Cl were used as starting materials, applying a combination of azide and mineralizer routes. The structure elucidation of BaP6 N10 NH (P63 , a=7.5633(11), c=8.512(2) Å, Z=2) was performed by a combination of transmission electron microscopy and single-crystal diffraction with microfocused synchrotron radiation. Phase purity was verified by Rietveld refinement. 1 H and 31 P solid-state NMR and FTIR spectroscopy are consistent with the structure model. The chemical composition was confirmed by energy-dispersive X-ray spectroscopy and CHNS analyses. Eu2+ -doped samples of BaP6 N10 NH show blue emission upon excitation with UV to blue light (λem =460 nm, fwhm=2423 cm-1 ) representing unprecedented Eu2+ -luminescence of an imidonitride.

9.
Chemistry ; 26(10): 2204-2210, 2020 Feb 17.
Artículo en Inglés | MEDLINE | ID: mdl-31711269

RESUMEN

Understanding the origin and mechanisms of luminescence is a crucial point when it comes to the development of new phosphors with targeted luminescence properties. Herein, a new phosphor belonging to the substance class of alkali metal lithosilicates with the generalized sum formula Cs4-x-y-z Rbx Nay Liz [Li3 SiO4 ]4 :Eu2+ is reported. Single crystals of the cyan-emitting UCr4 C4 -type phosphor show a peculiar double-band luminescence with one ultranarrow emission band at 473 nm and a narrow emission band at 531 nm under excitation with UV light (λexc =408 nm). Regarding occupation of the channels by the light metal ions, investigations of single-crystal XRD data led to the assumption that domain formation with distinct lithium- and sodium-filled channels occurs. Depending on which of these channels hosts the activator ion Eu2+ , a green or blue emission results. The herein-presented results shed new light on the luminescence process in the well-studied UCr4 C4 -type alkali metal lithosilicate phosphors.

10.
Chemphyschem ; 21(14): 1515-1518, 2020 07 17.
Artículo en Inglés | MEDLINE | ID: mdl-32501625

RESUMEN

We report infrared spectra of xylylene isomers in the gas phase, using free electron laser (FEL) radiation. All xylylenes were generated by flash pyrolysis. The IR spectra were obtained by monitoring the ion dip signal, using a IR/UV double resonance scheme. A gas phase IR spectrum of para-xylylene  was recorded, whereas ortho- and meta-xylylene were found to partially rearrange to benzocyclobutene and styrene. Computations of the UV oscillator strength  for all molecules were carried out and provde an explanation for the observation of the isomerization products.

11.
Angew Chem Int Ed Engl ; 59(41): 18240-18243, 2020 Oct 05.
Artículo en Inglés | MEDLINE | ID: mdl-32644230

RESUMEN

(Oxo)Nitridophosphates have recently been identified as a promising compound class for application in the field of solid-state lighting. Especially, the latest medium-pressure syntheses under ammonothermal conditions draw attention of the semiconductor and lighting industry on nitridophosphates. In this contribution, we introduce hot isostatic presses as a new type of medium-pressure synthetic tool, further simplifying nitridophosphate synthesis. In a second step, phosphorus nitride was replaced as starting material by red phosphorus, enabling the synthesis of Ca2 PN3 as model compound, starting only from readily available compounds. Moreover, first luminescence investigations on Eu2+ -doped samples reveal Ca2 PN3 :Eu2+ as a promising broad-band red-emitter (λem =650 nm; fwhm=1972 cm-1 ). Besides simple handling, the presented synthetic method offers access to large sample volumes, and the underlying reaction conditions facilitate single-crystal growth, required for excellent optical properties.

12.
Chemistry ; 25(63): 14382-14387, 2019 Nov 13.
Artículo en Inglés | MEDLINE | ID: mdl-31478260

RESUMEN

The lanthanum oxonitridophosphate La21 P40 O46 N57 was synthesized by high-pressure metathesis from partially hydrolysed LiPN2 and LaCl3 at 750-950 °C and 7-9 GPa. The combination of transmission electron microscopy (TEM) and diffraction using microfocused synchrotron radiation revealed a monoclinic crystal structure (space group P21 /n, a=14.042(4), b=7.084(3), c=41.404(10) Å, ß=97.73(3)° and Z=2), which is characterized by loop-branched 21 member single chains of P(O,N)4 tetrahedra that extend along [2 0 1]. These chains are related to the loop-branched dreier single chains with dreier-ring loops in stillwellite (CeBSiO5 ). In La21 P40 O46 N57 , these chains are characterized by a complex long-periodic conformation and exhibit disorder that involves La/N and P split positions. This is an extraordinarily long periodicity with respect to branched single chains of tetrahedra. La21 P40 O46 N57 constitutes the first rare-earth oxonitridophosphate exhibiting a chain structure. Single-crystal data are consistent with electron and powder X-ray diffraction.

13.
Chembiochem ; 19(6): 540-544, 2018 03 16.
Artículo en Inglés | MEDLINE | ID: mdl-29205716

RESUMEN

The relatively low chemical stability of cytosine compared with other nucleobases is a key concern in origin-of-life scenarios, but the effect of pressure on the rate of hydrolysis of cytosine to uracil remains unknown. Through in situ NMR spectroscopy measurements, it has been determined that the half-life of cytosine at 373.15 K decreases from (18.0±0.7) days at ambient pressure (0.1 MPa) to (8.64±0.18) days at high pressure (200 MPa). This yields an activation volume for hydrolysis of (-11.8±0.5) cm3 mol-1 ; a decrease that is similar to the molar volume of water (18.0 cm3 mol-1 ) and consistent with a tetrahedral 3,3-hydroxyamine transition-state/intermediate species. Similar behaviour was also observed for cytidine. At both ambient and high pressures, the half-life of cytosine decreases significantly as the pH decreases from 7.0 to 6.0. These results provide scant support for the notion that RNA-based life forms originated in high-temperature, high-pressure, acidic environments.


Asunto(s)
Citosina/química , Uracilo/química , Concentración de Iones de Hidrógeno , Hidrólisis , Resonancia Magnética Nuclear Biomolecular , Presión
14.
Chemistry ; 24(53): 14275-14281, 2018 Sep 20.
Artículo en Inglés | MEDLINE | ID: mdl-30004596

RESUMEN

Nitridophosphates and imidonitridophosphates show intriguing structural diversity, including unprecedented structure types. Highly condensed strontium imidonitridophosphate SrP3 N5 NH has been synthesized at 8 GPa and 1100 °C using a high-pressure high-temperature approach starting from stoichiometric amounts of Sr(N3 )2 , P3 N5 and NH4 Cl. Herein, NH4 Cl was used as a hydrogen source and as a precursor for in situ formation of SrCl2 , which acts as mineralizer and facilitates growth of single-crystals with a diameter of ≤30 µm. SrP3 N5 NH (P21 /c (no. 14), a=5.01774(2), b=8.16912(4), c=12.70193(5) Å, ß=101.7848(3)°, Z=4) adopts an unprecedented network structure, represented by the point symbol (3.4.5.6.72 )(3.4.5.72 .8)(3.6.73 .8). This unique three nodal P/N(H) network is stabilized by moderately strong hydrogen bonds causing a structure-directing effect, which has not yet been reported for imidonitridophosphates.

15.
Chemistry ; 24(30): 7647-7652, 2018 May 28.
Artículo en Inglés | MEDLINE | ID: mdl-29528193

RESUMEN

We investigate the self-reaction of benzyl, C7 H7 , in a high-temperature pyrolysis reactor. The work is motivated by the observation that resonance-stabilized benzyl radicals can accumulate in reactive environments and contribute to the formation of polycyclic aromatic hydrocarbons (PAHs) and soot. Reaction products are detected by IR/UV ion dip spectroscopy, using infrared radiation from the free electron laser FELIX, and are identified by comparison with computed spectra. Among the reaction products identified by their IR absorption are several PAHs linked to toluene combustion such as bibenzyl, phenanthrene, diphenylmethane, and fluorene. The identification of 9,10-dihydrophenanthrene provides evidence for a mechanism of phenanthrene formation from bibenzyl that proceeds by initial cyclization rather than an initial hydrogen loss to stilbene.

16.
Chemistry ; 24(51): 13596-13606, 2018 Sep 12.
Artículo en Inglés | MEDLINE | ID: mdl-29806207

RESUMEN

A series of aliphatic and aromatic thioethers and dithioethers of s-triazine were synthesised to study their thermal properties, in particular the thermally induced thiyl radical generation ability. Four symmetric s-triazine sulfides of the type (RS)3 C3 N3 , namely 2,4,6-tris(phenylthio)- (1), 2,4,6-tris(para-tolylthio)- (3), 2,4,6-tris(ethylthio)- (5) and 2,4,6-tris(tert-butylthio)-1,3,5-triazine (7), as well as four symmetric s-triazine disulfides of the type (RSS)3 C3 N3 , namely 2,4,6-tris(phenyldithio)- (2), 2,4,6-tris(para-tolyldithio)- (4), 2,4,6-tris(ethyldithio)- (6) and 2,4,6-tris(tert-butyldithio)-1,3,5-triazine (8) were synthesised. All compounds were comprehensively characterised by 1 H and 13 C NMR, infrared and Raman spectroscopy as well as elemental analyses. Single-crystal X-ray diffraction analyses of 1, 2 and 5 are discussed. The thermal behaviour was studied by thermogravimetric analyses coupled with mass spectrometry (TGA-MS) and quantum chemical calculations. Limiting oxygen index (LOI) flammability tests showed that the disulfides are the most promising radical generators, and are most likely suitable flame retardants for selected polymers.

17.
Angew Chem Int Ed Engl ; 57(41): 13676-13680, 2018 Oct 08.
Artículo en Inglés | MEDLINE | ID: mdl-30102467

RESUMEN

A hitherto unknown synthetic access to alkali lithosilicates, a substance class first described by Hoppe in the 1980s, is reported. With the synthesis and characterization of NaK7 [Li3 SiO4 ]8 , a new representative has been discovered, expanding the family of known alkali lithosilicates. Astonishingly, NaK7 [Li3 SiO4 ]8 and the already established alkali lithosilicates Na[Li3 SiO4 ] as well as K[Li3 SiO4 ] display unforeseen luminescence properties, when doped with Eu2+ . Na[Li3 SiO4 ]:Eu2+ exhibits an ultra-narrow blue, K[Li3 SiO4 ]:Eu2+ a broadband, and NaK7 [Li3 SiO4 ]8 :Eu2+ a yellow-green double emission upon excitation with near-UV to blue light. Consequently, all of the investigated substances of this class of compounds are highly interesting phosphors for application in phosphor converted LEDs.

18.
Chemistry ; 23(53): 13131-13140, 2017 Sep 21.
Artículo en Inglés | MEDLINE | ID: mdl-28692134

RESUMEN

Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. The fragmentation of the ions is dominated by loss of CO, C2 H4 , and C2 H5 , leading to daughter ions at m/z 56 and 55. Exploring the C5 H8 O.+ potential energy surface reveals hydrogen tunneling to play an important role in low-energy decarbonylation and probably also in the ethene-loss processes, yielding 1-butene and methylketene cations, respectively. At higher energies, pathways without a reverse barrier open up to oxopropenyl and cyclopropanone cations by ethyl-radical loss and a second ethene-loss channel, respectively. A statistical Rice-Ramsperger-Kassel-Marcus model is employed to test the viability of this mechanism. The pyrolysis of cyclopentanone is studied at temperatures ranging from about 800 to 1100 K. Closed-shell pyrolysis products, namely 1,3-butadiene, ketene, propyne, allene, and ethene, are identified based on their photoion mass-selected threshold photoelectron spectrum. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. A reaction mechanism is derived incorporating both stable and reactive species, which were not predicted in prior computational studies.

19.
Chemistry ; 23(36): 8658-8668, 2017 Jun 27.
Artículo en Inglés | MEDLINE | ID: mdl-28386991

RESUMEN

One of the key challenges in renewable chemical production is the conversion of lignin, especially by fast pyrolysis. The complexity of the lignin pyrolysis process has hindered the elucidation of the mechanism, inhibiting further industrial implementation. By combining pyrolysis of model compounds (4-phenoxyphenol and 2-methoxy-phenoxybenzene) with lignin bond characteristics both under vacuum and under realistic pressure conditions, the roles of inter- and intramolecular reactions were established. On the one hand, the stable 4-O-5 ether bond enables, without breaking, C-C bond formation and even directly forms naphthalene depending on the position and type of the substituent. p-Benzoquinone intermediates, on the other hand, are highly unstable at ambient pressure and directly decompose into coke and carbon monoxide. The system pressure (radical concentration) plays a crucial role in the dominant reaction mechanism by initiating intramolecular reactions, interfering with intramolecular reactions. H-transfer and recombination reactions suppress the decarbonylation of phenoxy radicals, thus yielding a very different product distribution.


Asunto(s)
Lignina/química , Benzoquinonas/química , Calor , Estructura Molecular , Éteres Fenílicos/química , Presión
20.
Chemistry ; 23(40): 9592-9599, 2017 Jul 18.
Artículo en Inglés | MEDLINE | ID: mdl-28543928

RESUMEN

Li12 P3 N9 was synthesized by solid-state reaction of Li3 N and P3 N5 at 790 °C. It is made up of non-condensed [P3 N9 ]12- dreier-rings of PN4 -tetrahedra. The corresponding high-pressure polymorph, Li4 PN3 , was synthesized under high-pressure/high-temperature conditions from Li12 P3 N9 or LiPN2 and Li7 PN4 at 6 or 7 GPa, respectively, using the multianvil technique. Li4 PN3 is the first lithium catena-nitridophosphate and contains PN3 zweier-chains of corner sharing PN4 -tetrahedra. To confirm the structure elucidated from single-crystal X-ray data, Rietveld refinement, 6 Li, 7 Li, and 31 P solid-state NMR spectroscopy, FTIR spectroscopy and EDX measurements were carried out. To examine the phase transition of Li12 P3 N9 to Li4 PN3 at 6 GPa and to corroborate the latter as the corresponding high-pressure polymorph, DFT calculations were conducted. Electronic band gap and electron localization function (ELF) calculations were carried out to elucidate the electronic properties and bonding behavior of both polymorphs.

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