Hydrogen-free melaminate salts M3(C3N6) (M = Cd, Ca) were synthesized in laser-heated diamond anvil cells at 34-48 GPa and 2000-2500 K. Cd3(C3N6) was synthesized via a direct reaction between the elements, while Ca3(C3N6) was obtained following a rational chemical design approach from calcium carbodiimide, Ca(NCN), which served as a single-source precursor. Both compounds contain the fully deprotonated melaminate anion (C3N6)6-, representing a fundamental milestone in nitridocarbonate chemistry. The crystal structures of M3(C3N6) were solved and refined using synchrotron single-crystal X-ray diffraction data and were fully corroborated by density functional theory calculations. Cd3(C3N6) crystallizes in the acentric R3c and Ca3(C3N6) in the centrosymmetric R3̅c space groups, and both compounds are recoverable to ambient conditions. Extending this design principle, our calculations indicate that Zn and Pb melaminates are thermodynamically accessible under similar conditions, highlighting the general stability of hydrogen-free nitridocarbonates of selected divalent metals.

The transport of carbon into the deep Earth is governed by the stability and properties of carbon-bearing phases. However, despite extensive research efforts, it is still an open question whether there are high-pressure minerals that can incorporate both silicon and carbon simultaneously. Multiple theoretical studies suggest that Si─C─O compounds could be stabilized at high pressures, but so far, no reliable experimental evidence for their presence has been presented. Here, we demonstrate that at 40(2) gigapascals and ≈ 1800(200) kelvin, CO2 reacts with silicic acid or cristobalite and forms the anhydrous silicon carbonate Si[CO3]2. The structure consists of [SiO6] octahedra coordinated by six [CO3]2- groups. Similar groups occur in many ambient and high-pressure carbonates, suggesting that mixed carbonate-silicate phases may be stable at midmantle pressures. Silicon carbonate decomposes upon decompression at pressures of <6 gigapascals but could act as a potential host for carbon in Earth's lower mantle.

Synthesis at extreme conditions enables access to nitrogen-rich carbon-nitrogen anions that cannot be obtained at ambient conditions. Here, through a direct reaction between Eu(N3)2 and EuC2 with Fe in a laser-heated diamond anvil cell (DAC) at 50(3) GPa, we synthesized the first inorganic hydrogen-free pyronitridocarbonate, Eu4Fe x (C2N5)2, x = 0.864(6), featuring novel highly charged [C2N5]7- anions, along with the first stoichiometric oxygen-free rare-earth metal guanidinate Eu5(CN3)3. The crystal structures of both compounds were determined via synchrotron single-crystal X-ray diffraction (SCXRD) and fully corroborated by density functional theory (DFT) calculations. Eu4Fe x (C2N5)2 was found to be recoverable at pressures close to ambient. Keeping the sample at ambient conditions for 1 day leads to splitting of half of the [C2N5]7- units in Eu4Fe x (C2N5)2 into the guanidinate [CN3]5- and carbodiimide [CN2]2- anions. The statistical analysis of the multigrain SCXRD data and DFT-based electronic structure analysis well defined the chemical nature of the bonding in [C2N5]7- and [CN3]5- anions. This study provides a clear synthetic pathway to a new class of inorganic nitridocarbonates.

Molecular nitrogen exhibits remarkable structural diversity near the polymeric transition, where multiple phases are metastable. Here, we report two new molecular phases. The first, tζ-N_2, is a polytype of monoclinic C2/c ζ-N_2, characterized by a tripled c axis and 96 atoms per unit cell. The second, ξ-N_2, is a previously unreported hexagonal phase (P6cc) containing 112 atoms per unit cell. Both phases were synthesized in a diamond anvil cell by laser heating ζ-N_2 to 1800–2500 K at pressures of 78–98 GPa. Their crystal structures were determined using single-crystal X-ray diffraction, corroborated by Raman spectroscopy, and supported by first-principles calculations. The tζ-N_2 phase likely corresponds to the previously reported κ-N_2 phase.

High-pressure high-temperature synthesis in laser-heated diamond anvil cells provides a direct pathway to stabilize polymeric and oligomeric nitrogen units, often inaccessible under ambient conditions due to the stability of the N2 molecule. Here we report the high-pressure reactivity of antimony with molecular nitrogen, leading to the discovery of two distinct binary nitrides. At megabar pressures, we synthesized and structurally characterized mP20-Sb2(N8), the first pnictogen oligonitride containing unprecedented twisted single-bonded (N8)10- chains. The compound was identified by single-crystal x-ray microdiffraction and Raman spectroscopy, supported by density functional theory calculations. At lower pressures of ∼ 50 GPa, we observed the formation of oC32-Sb3N5, complementing recent reports of this phase by the studies of its compressional behavior and stability field. These results significantly expand the interpnictogen chemistry and demonstrate the ability of antimony to stabilize unusual extended nitrogen fragments at high pressures.

Tin and germanium carbonates, Sn[CO3]2 and Ge[CO3]2, were synthesized by the reaction of SnO2 or GeO2 with CO2 at high pressures and high temperatures in a laser-heated diamond anvil cell. Their structures were solved by in situ single-crystal X-ray diffraction at high pressures. Sn[CO3]2 formed at similar to 30 GPa, while Ge[CO3]2 formed at around 44 GPa. Both carbonates are isostructural and crystallize in the trigonal space group P3. The distinguishing feature of the Sn[CO3]2 or Ge[CO3]2 structures is the presence of isolated [CO3]2- groups, which are arranged in layers. Both structures contain octahedrally coordinated tetravalent Sn4+ and Ge4+ cations in two positions with partial site occupation. Bulk moduli of both carbonates are K 0 approximate to 44-48 GPa. Full geometry optimizations based on DFT calculations reproduced the crystal structures. The DFT models were used to complement the experimental compression data and for the assignment of Raman modes. Both Sn and Ge carbonates can be recovered under ambient conditions after pressure release.

Two anhydrous tellurium carbonates, Te[CO3]O and Te4O7[CO3], have been synthesized in laser-heated diamond anvil cells by a reaction of TeO2 with CO2. Te[CO3]O was obtained at higher pressures (40(2) GPa), while Te4O7[CO3] was synthesized at moderate pressures (20(2) GPa). The crystal structures of both compounds were determined from synchrotron single crystal X-ray diffraction data and confirmed by density functional theory-based calculations. For Te[CO3]O the experimental Raman data were accurately reproduced by a Raman spectrum derived from the calculations. Both carbonates belong to the family of sp2-carbonates and are characterized by the presence of trigonal-planar [CO3]2--groups. While the crystal structure of Te[CO3]O is rather simple, Te4O7[CO3] is a layered compound with layers of [CO3]2--groups alternating with complex Te-O-layers. Our DFT-based calculations show that stereochemically active lone electron pairs are present in both crystal structures at elevated pressures. The successful synthesis of Te[CO3]O is a significant enlargement of the crystal chemistry of carbonates, as it demonstrates that anhydrous carbonates of chalcogenide group elements hosting no further cations can be synthesized. Excluding the noble gases, the chalcogenide group was the last main group of the periodic table where such carbonates were not known up to now.

A high-pressure polymorph of boron oxide, B2O3-P212121, has been obtained in a laser-heated diamond anvil cell at 50(3) GPa after heating boron trioxide to a temperature of Tmax ≤ 2500(300) K. The crystal structure was determined from synchrotron single crystal X-ray diffraction and was confirmed by a combination of density functional theory (DFT) calculations and experimental Raman spectroscopy. Experimental- as well as DFT-data confirm the non-centrosymmetric/non-polar space group P212121. The structural model of B2O3-P212121 is in agreement with an earlier DFT-based crystal structure prediction. The crystal structure is characterized by corner-sharing [BO4] tetrahedra with covalent B-O bonds. Our experimental Raman data show that B2O3-P212121 can be recovered under ambient conditions.

It is well established that a significant amount of heat produced in the Earth’s mantle is due to the decay of uranium. However, uranium cannot be incorporated in large amounts into the most common mantle minerals. Here, we suggest that carbonates could be host phases for uranium in carbon-rich mantle lithologies. Two anhydrous uranium carbonates, U2[CO3]3 and U[CO3]2, were simultaneously synthesized by a reaction of UO2 with CO2 in a laser-heated diamond anvil cell at 20(1) GPa and 1800(200) K. Their crystal structures were obtained from synchrotron-based single crystal diffraction data and reproduced by density functional theory-based calculations. In U2[CO3]3 trivalent uranium cations are present, while uranium is four-valent in U[CO3]2. The synthesis of U2[CO3]3 and U[CO3]2 is a significant extension of the chemistry of uranium compounds and we provide a straightforward synthesis route for a UIII-containing compound. It is well established that a significant amount of heat produced in the Earth’s mantle is due to the decay of uranium, yet the incorporation of uranium in deep mantle phases remains poorly explored. Here, two chemically simple uranium carbonates (U2[CO3]3 and U[CO3]2) were synthesized by a reaction of UO2 with CO2 at lower mantle conditions, revealing that uranium carbonates could be host phases of uranium in carbon-rich lithologies in the Earth’s mantle.

The antimony oxide-carbonate Sb2O2[CO3] has been synthesized in a laser-heated diamond anvil cell by a reaction between Sb2O5, H2O, and C (diamond). Its crystal structure was determined by synchrotron single-crystal X-ray diffraction and confirmed by density functional theory (DFT) calculations in combination with experimental Raman spectroscopy. The structure of Sb2O2[CO3] is characterized by the presence of [CO3]2--groups and hence belongs to the family of sp 2-carbonates. The second building block of its crystal structure is interconnected "Sb2O5-units", which form a Sb & horbar;O-network within the b, c lattice plane. Our DFT calculations show the presence of stereochemically active lone electron pairs approximate to 0.7 & Aring; away from the Sb3+-cations. The synthesis of Sb2O2[CO3] is a significant enlargement of the crystal chemistry of carbonates, as (oxide-)carbonates of antimony have not been described up to now, and it also allows us to study the influence of the presence of lone electron pairs on crystal structures at elevated pressures.

Die Hochdruck‐Hochtemperatur‐Synthese in laserbeheizten Diamantstempelzellen ermöglicht die direkte Stabilisierung polymerer und oligomerer Stickstoffeinheiten, die aufgrund der Stabilität des N 2 Moleküls unter Umgebungsbedingungen oft nicht zugänglich sind. Hier berichten wir über die Reaktion von Antimon bei höheren Drücken mit molekularem Stickstoff, die zur Entdeckung zweier unterschiedlicher binärer Nitride führte. Bei Megabar‐Drücken synthetisierten und charakterisierten wir mP 20‐Sb 2 (N 8 ), das erste Pniktogen‐Oligonitrid mit bisher unbekannten verdrehten und einfach gebundenen (N 8 ) 10− Ketten. Die Verbindung wurde mittels Einkristall‐Röntgenmikrodiffraktion und Raman‐Spektroskopie identifiziert und durch Berechnungen mittels Dichtefunktionaltheorie bestätigt. Bei niedrigeren Drücken von ∼50 GPa beobachteten wir die Bildung oC 32‐Sb 3 N 5 und ergänzen damit kürzlich veröffentlichte Daten zu dieser Phase durch Untersuchungen des Kompressionsverhaltens und Stabilitätsfeldes. Diese Ergebnisse erweitern die Interpniktogenchemie erheblich und demonstrieren die Fähigkeit von Antimon ungewöhnlich erweiterte Stickstofffragmente bei hohen Drücken zu stabilisieren.

B 2 O 3 - P 2 1 2 1 2 1 is a high-pressure boron trioxide polymorph with an acentric orthorhombic crystal structure and a high bulk modulus. It is characterized by [BO 4 ] building blocks and can be recovered under ambient conditions together with B 2 O 3 - Ccm 2 1 .

High‐pressure high‐temperature synthesis in laser‐heated diamond anvil cells provides a direct pathway to stabilize polymeric and oligomeric nitrogen units, often inaccessible under ambient conditions due to the stability of the N 2 molecule. Here we report the high‐pressure reactivity of antimony with molecular nitrogen, leading to the discovery of two distinct binary nitrides. At megabar pressures, we synthesized and structurally characterized mP 20‐Sb 2 (N 8 ), the first pnictogen oligonitride containing unprecedented twisted single‐bonded (N 8 ) 10− chains. The compound was identified by single‐crystal x‐ray microdiffraction and Raman spectroscopy, supported by density functional theory calculations. At lower pressures of ∼ 50 GPa, we observed the formation of oC 32‐Sb 3 N 5 , complementing recent reports of this phase by the studies of its compressional behavior and stability field. These results significantly expand the interpnictogen chemistry and demonstrate the ability of antimony to stabilize unusual extended nitrogen fragments at high pressures.

The chemical evolution of Earth’s mantle is governed by the interplay between primordial reservoirs formed during accretion and recycled components introduced by subduction. While helium and hydrogen isotopic anomalies strongly suggest the existence of primordial deep-water reservoirs, the mineral hosts capable of sequestering hydrogen during crystallization of basal magma ocean remain elusive. Here we use high-pressure and high-temperature experiments in laser-heated diamond anvil cells and report the synthesis of two hexagonal iron oxyhydroxides, Fe5O12Hx and Fe7O12Hx, under lowermost mantle conditions. We demonstrate that these phases can form under water-undersaturated conditions and exhibit high densities that facilitate gravitational settling. Capable of hosting both primordial and recycled water, these dense oxyhydroxides provide a plausible mineralogical basis for the seismically observed ultralow-velocity zones at the core–mantle boundary. Furthermore, their stability provides a mechanism for the transport of volatiles into Earth’s core or their episodic release into mantle plumes. Therefore, deep mantle iron oxyhydroxides may play a critical role in modulating planetary volatile cycles throughout geological time. Dense iron oxyhydroxide phases may form from an early basal magma ocean, trapping water and potentially contributing to the formation of thermochemical anomalies in the deep mantle, according to high-pressure and high-temperature experiments.

High-pressure high-temperature synthesis in laser-heated diamond anvil cells provides a direct pathway to stabilize polymeric and oligomeric nitrogen units, often inaccessible under ambient conditions due to the stability of the N2 molecule. Here we report the high-pressure reactivity of antimony with molecular nitrogen, leading to the discovery of two distinct binary nitrides. At megabar pressures, we synthesized and structurally characterized mP20-Sb2(N8), the first pnictogen oligonitride containing unprecedented twisted single-bonded (N8)10- chains. The compound was identified by single-crystal x-ray microdiffraction and Raman spectroscopy, supported by density functional theory calculations. At lower pressures of similar to 50 GPa, we observed the formation of oC32-Sb3N5, complementing recent reports of this phase by the studies of its compressional behavior and stability field. These results significantly expand the interpnictogen chemistry and demonstrate the ability of antimony to stabilize unusual extended nitrogen fragments at high pressures.

High-pressure synthesis provides unique pathways to materials with unprecedented structures and properties. Here we report the synthesis and structural characterization of novel rare-earth (La, Sm, Gd, Dy) chlorides, chloride carbides, and oxychloride phases obtained due to complex chemical reactions in diamond anvil cells after laser heating of rare-earth metals and NaCl at pressures of 39-127 GPa and temperatures of 2500-2800 K. Synchrotron single-crystal X-ray diffraction analysis allowed us to solve previously unknown crystal structures of binary (La2Cl, LaCl, LaCl3, DyCl) and ternary (DyNa2Cl5, Sm2ClC2, Gd2ClC2, Dy2ClC2, Sm19ClC18, Gd19ClC18, Dy5Cl3C, DyOCl) compounds. Significantly, we identified trans-polyacetylene-like carbon chains in lanthanide chloride carbides, a structural motif previously hypothesized but not observed experimentally. Our findings highlight the enhanced chemical reactivity of alkali halides under extreme conditions, uncovering novel chemical bonding and expanding the landscape of potential functional materials accessible through high-pressure synthesis.

AbstractDie Reaktion von Praseodym(IV)‐oxid und Sauerstoff bei 27 GPa in einer Diamantstempelzelle lieferte das Oxid Peroxid Pr2IV(O2)O3, welches bei unterschiedlichen Druckpunkten durch Einkristallstrukturanalyse an multikristallinem Material, Ramanspektroskopie sowie durch quantenchemische Rechnungen charakterisiert wurde. Die Anwesenheit vierwertiger Praseodymionen wird durch Berechnungen der elektronischen Struktur unterstützt, die eine Bandlücke von ca. 1,2 eV vorhersagen, was mit dem antizipierten chemischen Modell eines ionischen Festkörpers übereinstimmt. Pr2(O2)O3 stellt die bislang sauerstoffreichste binäre Verbindung eines Lanthanoids mit Sauerstoff dar und ist das erste Beispiel eines Peroxidanions neben Pr4+. Darüber hinaus demonstrieren diese Ergebnisse, dass Sauerstoff eine Komproportionierung eingeht um Peroxidionen zu bilden, bevor die Praseodymionen über die Oxidationsstufe +IV hinaus oxidiert werden. Die direkte Oxidation der Oxidionen durch Pr4+ wurde durch ein Kontrollexperiment in Argon anstelle von Sauerstoff ausgeschlossen, in welchem keine Oxidation der Oxidionen beobachtet wurde.

For the activation of nitrogen and its reduction to ammonia, transition metals are crucial in biological as well as industrial processes. So far, only a few binary transition metal compounds with nitrogen dimer anions are known, whereas a ternary compound has remained undiscovered as yet. Here, we report on the synthesis and properties of the first ternary transition metal compound, namely, BeW10N14(N2), which exhibits dinitrogen anions. It was synthesized in a high-temperature high-pressure approach from W2Be4N5. The crystal structure, elucidated with synchrotron radiation, unites WN7 capped trigonal prisms with intriguing BeN6 octahedra and (N2)-anions. Elastic and electronic properties of the title compound were corroborated by DFT calculations, revealing simultaneous ultra-incompressible and metallic behavior. The synthesis and investigation of the first ternary transition metal nitride with dinitrogen units opens the door to a new field of research on nitride and pernitride chemistry.