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Nitridophosphates and nitridogermanates attract high interest in current research due to their structural versatility. Herein, the elastic properties of GeP 2 N 4 were investigated by single-crystal X-ray diffraction (XRD) upon compression to 44.4(1) GPa in a diamond anvil cell. Its isothermal bulk modulus was determined to be 82(6) GPa. At 44.4(1) GPa, laser heating resulted in the formation of multiple crystalline phases, one of which was identified as unprecedented germanium nitridophosphate GePN 3 . Its structure was elucidated from single-crystal XRD data ( C 2/ c (no. 15), a = 8.666(5), b = 8.076(4), c = 4.691(2) Å, β = 101.00(7)°) and is built up from layers of GeN 6 octahedra and PN 4 tetrahedra. The GeN 6 octahedra form double zigzag chains, while the PN 4 tetrahedra are found in single zigzag chains. GePN 3 can be recovered to ambient conditions with a unit cell volume increase of about 12%. It combines P V and Ge IV in a condensed nitridic network for the first time.

We report on the synthesis of two-layered alkali germanates, Na 2 Ge 4 O 7 and K 2 Ge 4 O 7 . Both compounds were synthesized by using the ammonothermal method at 823 K and 100 MPa. Under these conditions, germanium is partially reduced from the +IV state to +II, forming mixed-valence compounds with the rarely observed [Ge (II) O 3 ] 4- unit. The valence state was verified by X-ray photoelectron spectroscopy (XPS) and was accompanied by theoretical calculations alongside vibrational spectroscopy and single-crystal X-ray structure determination. The compounds crystallize in the trigonal space groups (Na 2 Ge 4 O 7 : P 3̅ c 1 and K 2 Ge 4 O 7 : P 3̅ m 1) and feature layers of corner sharing [Ge (II) O 3 ] 4- and [Ge (IV) 2 O 7 ] 6- units forming [Ge (II) 2 Ge (IV) 2 O 7 ] 2- polyanions. These layers are separated by alkali metal ions. The compounds are colorless insulators with band gaps of 4.0-4.2 eV. According to the Robin-Day classification, both compounds can be described as class I materials, where the valences are trapped on specific sites.

High-pressure, high-temperature (HP/HT) syntheses are essential for modern high-performance materials. Phosphorus nitride, nitridophosphate, and more generally nitride syntheses benefit greatly from HP/HT conditions. In this contribution, we present the first systematic in situ investigation of a nitridophosphate HP/HT synthesis using the reaction of zinc nitride Zn 3 N 2 and phosphorus(V) nitride P 3 N 5 to the nitride semiconductor Zn 2 PN 3 as a case study. At a pressure of 8 GPa and temperatures up to 1300 °C, the reaction was monitored by energy-dispersive powder X-ray diffraction (ED-PXRD) in a large-volume press at beamline P61B at DESY. The experiments investigate the general behavior of the starting materials under extreme conditions and give insight into the reaction. During cold compression and subsequent heating, the starting materials remain crystalline above their ambient-pressure decomposition points, until a sufficient minimum temperature is reached and the reaction starts. The reaction proceeds via ion diffusion at grain boundaries with an exponential decay in the reaction rate. Raising the temperature above the minimum required value quickly completes the reaction and initiates single-crystal growth. After cooling and decompression, which did not influence the resulting product, the recovered sample was analyzed by energy-dispersive X-ray (EDX) spectroscopy.

In this work, we present the synthesis, characterization, and optical properties of Sr 5 Si 7 P 2 N 16 :Eu 2+ , the first tetrahedral (Si,P)-N network in which Si occupies more than 50% of the tetrahedra. While past studies have shown progress with anionic (Si,P)-N networks, the potential of silicon-rich compounds remains untapped. The synthesized compound Sr 5 Si 7 P 2 N 16 exhibits a unique mixture of substitutional order and positional disorder within its network. The analytical challenges posed by the similarities between Si 4+ and P 5+ , along with the network's disorder, were overcome by combining single-crystal X-ray diffraction and scanning transmission electron microscopy EDX mapping. Low-cost crystallographic calculations provided additional insights into the identification of tetrahedral occupations in mixed networks. Luminescence investigations on Sr 5 Si 7 P 2 N 16 :Eu 2+ revealed yellow emission, adding to the known blue, green, and orange emission maxima of Sr-(Si,P)-N networks, highlighting the variability of such compounds.

Combining different anions in one material allows tuning of its structural, magnetic, and electronic properties. We hereby present the mixed anion compound Sr 2 BN 2 H, expanding the less-known class of nitridoborate hydrides. Solid-state reaction of Sr 2 N, BN, and SrH 2 at 850 °C in a tube furnace yielded a gray, air- and moisture-sensitive powder of Sr 2 BN 2 H. It crystallizes as colorless platelets in the orthorhombic space group Pnma (no. 62) with a = 9.9164(2), b = 3.9079(1), and c = 10.1723(2) Å and Z = 4. An initial structural model was obtained from single-crystal X-ray diffraction data and corroborated by neutron powder diffraction data of the corresponding deuteride. Further validation by 1 H and 11 B MAS NMR, FTIR, and Raman spectroscopy complements the structural proof of anionic hydrogen present in the compound. Quantum chemical calculations support the experimental findings and reveal the electronic structure of Sr 2 BN 2 H.

In this work, we present a computational protocol that is able to predict the experimental absorption and emission spectral shapes of Eu 2+ -doped phosphors. The protocol is based on time-dependent density functional theory and operates in conjunction with an excited-state dynamics approach. It is demonstrated that across the study set consisting of representative examples of nitride, oxo-nitride, and oxide Eu 2+ -doped phosphors, the energy distribution and the band shape of the emission spectrum are related to the nature of the 4f-5d transitions that are probed in the absorption process. Since the 4f orbitals are very nearly nonbonding, the decisive quantity is the covalency of the 5d acceptor orbitals that become populated in the electronically excited state that leads to emission. The stronger the (anti) bonding interaction between the lanthanide and the ligands is in the excited state, the larger will be the excited state distortion. Consequently, the corresponding emission will get broader due to the vibronic progression that is induced by the structural distortion. In addition, the energy separation of the absorption bands that are dominated by states with valence 4f-5d and a metal to ligand charge transfer character defines a measure for the thermal quenching of the studied Eu 2+ -doped phosphors. Based on this analysis, simple descriptors are identified that show a strong correlation with the energy position and bandwidth of the experimental emission bands without the need for elaborate calculations. Overall, we believe that this study serves as an important reference for designing new Eu 2+ -doped phosphors with desired photoluminescence properties.

A nanowire photoanode SrTaO 2 N, a semiconductor suitable for overall water-splitting with a band gap of 2.3 eV, was coated with functional overlayers to yield a core-shell structure while maintaining its one-dimensional morphology. The nanowires were grown hydrothermally on tantalum, and the perovskite-related oxynitride structure was obtained by nitridation. Three functional overlayers have been deposited on the nanowires to enhance the efficiency of photoelectrochemical (PEC) water oxidation. The deposition of TiO x protects the oxynitride from photocorrosion and suppresses charge-carrier recombination at the surface. Ni(OH) x acts a hole-storage layer and decreases the dark-current contribution. This leads to a significantly improved extraction of photogenerated holes to the electrode-electrolyte surface. The photocurrents can be increased by the deposition of a cobalt phosphate (CoP i ) layer as a cocatalyst. The heterojunction nanowire photoanode generates a current density of 0.27 mA cm -2 at 1.23 V vs the reversible hydrogen electrode (RHE) under simulated sunlight (AM 1.5G). Simultaneously, the dark-current contribution, a common problem for oxynitride photoanodes grown on metallic substrates, is almost completely minimized. This is the first report of a quaternary oxynitride nanowire photoanode in core-shell geometry containing functional overlayers for synergetic hole extraction and an electrocatalyst.

We report on the structure and properties of the lithium oxonitridosilicate oxide Li 4 Sr 4 [Si 4 O 4 N 6 ]O:Eu 2+ obtained from solid-state metathesis. The crystal structure was solved and refined from single-crystal X-ray data in the space group P4 2 / nmc (No. 137) [ Z = 2, a = 7.4833(6), c = 9.8365(9) Å, and R1(obs) = 0.0477]. The structure of Li 4 Sr 4 [Si 4 O 4 N 6 ]O:Eu 2+ is built up from a layered 2D network of SiN 3 O tetrahedra and exhibits stacking disorder. The results are supported by transmission electron microscopy and energy-dispersive X-ray spectroscopy as well as lattice energy, charge distribution, and density functional theory (DFT) calculations. Optical measurements suggest an indirect band gap of about 3.6 eV, while DFT calculations on a model free of stacking faults yield a theoretical electronic band gap of 4.4 eV. Samples doped with Eu 2+ exhibit luminescence in the orange spectral range (λ em ≈ 625 nm; full width at half-maximum ≈ 4164 cm -1 ; internal quantum efficiency at room temperature = 24%), extending the broad field of phosphor materials research toward the sparsely investigated materials class of lithium oxonitridosilicate oxides.

The oxonitridocarbidosilicates RE 4 Ba 2 [Si 12 O 2 N 16 C 3 ]:Eu 2+ ( RE = Lu, Y) were synthesized by carbothermal reactions starting from RE 2 O 3 , graphite, Ba 2 Si 5 N 8 , Si(NH) 2 , and Eu 2 O 3 . The crystal structure of Lu 4 Ba 2 [Si 12 O 2 N 16 C 3 ]:Eu 2+ was elucidated on a submicron-sized single crystal by a combination of transmission electron microscopy and microfocused synchrotron radiation. The compound crystallizes in trigonal space group P3 (no. 143) with a = 16.297(4) Å, c = 6.001(2) Å, and Z = 3 ( R1 = 0.0332, wR2 = 0.0834, GoF = 1.034). According to Rietveld refinements on powder X-ray diffraction data, Y 4 Ba 2 [Si 12 O 2 N 16 C 3 ]:Eu 2+ is isotypic with a = 16.41190(6) Å and c = 6.03909(3) Å. The crystal structures are built up of vertex-sharing SiC(O/N) 3 tetrahedra forming star-shaped units [C [4] (Si(O/N) 3 ) 4 ] with carbon atoms in fourfold bridging positions. Energy-dispersive X-ray spectroscopy and CHNS analysis correspond to the sum formula, lattice energy, and charge distribution calculations support the assignment of O/N/C atoms. When excited with UV to blue light, Eu 2+ -doped samples show green luminescence for RE = Lu (λ em ≈ 538 nm, full width at half-maximum (fwhm) ≈ 3600 cm -1 ) and yellow emission in the case of RE = Y (λ em ≈ 556 nm, fwhm ≈ 4085 cm -1 ).

We describe the oxonitridophosphates M 1- x PO 3+4 x N 1-4 x ( x ≈ 0.05) and the isotypic oxophosphates M 0.75 PO 4 ( M = Zr, Hf) obtained by high-pressure metathesis. The structures (ZrSiO 4 -type, space group I4 1 / amd (no. 141), a = 6.5335(7)-6.6178(12), c = 5.7699(7)-5.8409(9) Å, Z = 4) were refined from single-crystal X-ray diffraction data, and the powder samples were examined with quantitative Rietveld refinement. Infrared spectroscopy did not indicate the presence of X-H ( X = O, N) bonds. The optical band gaps, between 3.5 and 4.3 eV, were estimated from UV-vis data using the Kubelka-Munk function under assumption of a direct band gap. Temperature-dependent powder X-ray diffraction showed a phase transformation of the M 0.75 PO 4 ( M = Zr, Hf) compounds to ambient pressure polymorphs at 780 (Zr) and 900 °C (Hf). The preparation of the nitrogen containing compounds exemplifies the systematic access to the new class of group 4 nitridophosphates granted by high-pressure metathesis. Moreover, we show that high-pressure metathesis can also be used for the preparation of metastable oxophosphates.

The structural diversity of tetrahedra networks of phosphates can greatly be enhanced by introduction of mixed N/O anion positions. LiPr 2 P 4 N 7 O 3 exemplifies the benefits of N/O mixed anion positions as it is the first rare-earth (oxo)nitridophosphate with a single-layered structure and a degree of condensation (atomic ratio of tetrahedra centers (P) to tetrahedra corners (N/O atoms)) of 2/5. The compound was prepared through high-pressure metathesis starting from PrF 3 , LiPN 2 , Li 2 O, and PON using a hydraulic 1000t press and the multianvil technique. LiPr 2 P 4 N 7 O 3 crystallizes as pale-green single-crystals, from which its structure was determined (space group P2 1 / c (no. 14), a = 4.927(1), b = 7.848(2), c = 10.122(2) Å, β = 91.55(3)°, Z = 2, R 1 = 0.020, wR 2 = 0.045). The structure consists of single-layers of vertex-sharing Q 3 -type P(N/O) 4 tetrahedra forming four- and eight-membered rings arranged in the fashion of the Archimedean fes net. UV-vis spectroscopy revealed the typical Pr 3+ f -f transitions, leading to a pale-green color of the crystals. Moreover, the optical band gap was determined to 4.1(1) eV, assuming a direct transition. High-temperature powder X-ray diffraction showed the beginning of a gradual decomposition starting at ca. 500 °C.

The oxonitridosilicate oxides RE 26 Ba 6 [Si 22 O 19 N 36 ]O 16 :Eu 2+ (RE = Y, Tb) were synthesized by high-temperature reaction in a radiofrequency furnace starting from REF 3 , RE 2 O 3 (RE = Y, Tb), BaH 2 , Si(NH) 2 , and EuF 3 . The structure elucidation is based on single-crystal X-ray data. The isotypic materials crystallize in the monoclinic space group Pm (no. 6) [Z = 3, a = 16.4285(8), b = 20.8423(9), c = 16.9257(8) Å, β = 119.006(3)° for RE = Y and a = 16.5465(7), b = 20.9328(9), c = 17.0038(7) Å, β = 119.103(2)° for RE = Tb]. The unique silicate layers are made up from Q 1 -, Q 2 -, and Q 3 -type Si(O/N) 4 - as well as Q 4 -type SiN 4 -tetrahedra, forming three slightly differing types of cages. The corresponding 3-fold superstructure as well as pronounced hexagonal pseudosymmetry complicated the structure elucidation. Rietveld refinement on powder X-ray diffraction data, energy-dispersive X-ray spectroscopy and infrared spectroscopy support the findings from single-crystal X-ray data. When excited with UV to blue light, Y 26 Ba 6 [Si 22 O 19 N 36 ]O 16 :Eu 2+ shows broad orange-red luminescence (λ em = 628 nm, fwhm ≈ 125 nm/3130 cm -1 ). An optical band gap of 4.2 eV was determined for the doped compound by means of UV/vis spectroscopy.

La 24 Sr 14-7x [Si 36 N 72 ](O 1-x F x ) 14 with x = 0.489 was obtained as a microcrystalline product by metathesis at 1500 °C in a radio-frequency furnace starting from Si(NH) 2 , La(NH 2 ) 3 , SrH 2 , LaF 3 , and CeF 3 . The structure of the new nitridosilicate oxide fluoride was determined by combining transmission electron microscopy (TEM) and single-crystal X-ray diffraction using a microfocused synchrotron beam. The structure model with pronounced disorder [P6 3 /mmc, Z = 1, a = 16.2065(3), c = 9.4165(1) Å, R 1 (obs) = 0.0436] was confirmed by electron diffraction and aberration-corrected Z-contrast scanning TEM. The highly symmetric AB 2 framework, which was theoretically predicted but not yet realized, consists of all-side vertex-sharing SiN 4 tetrahedra that form channels along [001] filled with La, Sr, O, and F atoms. The connectivity pattern is related to that of tridymite. X-ray spectroscopy and bond-valence-sum calculations were further taken into account for assignment of the N, O, and F atoms.

Thorough investigation of nitridophosphates has rapidly accelerated through development of new synthesis strategies. Here we used the recently developed high-pressure metathesis to prepare the first rare-earth metal nitridophosphate, Ce 4 Li 3 P 18 N 35 , with a high degree of condensation >1/2. Ce 4 Li 3 P 18 N 35 consists of an unprecedented hexagonal framework of PN 4 tetrahedra and exhibits blue luminescence peaking at 455 nm. Transmission electron microscopy (TEM) revealed two intergrown domains with slight structural and compositional variations. One domain type shows extremely weak superstructure phenomena revealed by atomic-resolution scanning TEM (STEM) and single-crystal diffraction using synchrotron radiation. The corresponding superstructure involves a modulated displacement of Ce atoms in channels of tetrahedra 6-rings. The displacement model was refined in a supercell as well as in an equivalent commensurate (3 + 2)-dimensional description in superspace group P6 3 (α, β, 0)0(-α - β, α, 0)0. In the second domain type, STEM revealed disordered vacancies of the same Ce atoms that were modulated in the first domain type, leading to sum formula Ce 4-0.5x Li 3 P 18 N 35-1.5x O 1.5x (x ≈ 0.72) of the average structure. The examination of these structural intricacies may indicate the detection limit of synchrotron diffraction and TEM. We discuss the occurrence of either Ce displacements or Ce vacancies that induce the incorporation of O as necessary stabilization of the crystal structure.

High-pressure metathesis was proposed to be a gateway to the elusive class of rare-earth nitridophosphates. With this method the first ternary compounds of this class with sum formula RE2P3N7 were prepared, a melilite-type with RE = Pr, Nd, Sm, Eu, Ho, Yb (Ho2P3N7: P4̅21m, a = 7.3589(2), c = 4.9986(2) Å, Z = 2) and a Ba2Cu[Si2O7] structure type with RE = La, Ce, Pr (Pr2P3N7: monoclinic, C2/c, a = 7.8006(3), b = 10.2221(3), c = 7.7798(3) Å, β = 111.299(1)°, Z = 4). The phase relation between the two structure types was prior unknown and is here evidenced by experimental data as well as density functional theory calculations performed for the Pr2P3N7 compounds. Adequate classification of both structures types with regard to Liebau nomenclature, vertex symbol, and point symbol is made. Additionally, the tiling patterns of the monolayered structures are deducted. We demonstrate that high-pressure metathesis offers a systematic access to rare-earth nitridophosphates with an atomic ratio of P/N between 1/2 and 1/4.

Microcrystals of the oxonitridosilicate oxide La(11)Si(13)N(27.636)O(1.046):Ce(3+) were obtained by exploratory high-temperature synthesis starting from La, La(NH2)3, Si(NH)2, BaH2, and CeF3. Owing to the small size of the crystals, microfocused synchrotron radiation was used for structure investigations (space group Cmc21 (No. 36), a = 9.5074(4) Å, b = 32.0626(9) Å, c = 18.5076(8) Å, Z = 8, R1(all) = 0.0267). The crystal structure consists of an unprecedented interrupted three-dimensional network of vertex-sharing SiN(4-x)O(x) tetrahedra that form channels of siebener rings along [100]. Moreover, the structure is characterized by layers of condensed sechser rings in a boat conformation and vierer rings, which are alternatingly stacked with layers of vierer and dreier rings. Several split positions indicate two different local structure variants. Infrared spectroscopy confirms the absence of N-H bonds. Powder X-ray diffraction data show that bulk samples contain only a small amount of La(11)Si(13)N(27.636)O1.046:Ce(3+). However, once the exact composition was determined from structure analysis, it was possible to optimize the synthesis using fluorides as starting materials. Thereby, bulk samples of the homeotypic compound La(11)Si(13)N(27.376)O(0.936)F were obtained and investigated.

Two novel oxonitridophosphates M2PO3N with M = Ca and Sr were synthesized under high-pressure high-temperature (7 GPa and 1100 °C) using the multianvil technique or by solid-state reaction in the silica ampules (1100 °C) from amorphous phosphorus oxonitride (PON) and the respective alkaline earth oxides MO (M = Ca, Sr). The products represent the first examples of alkaline earth ortho-oxonitridophosphates containing noncondensed [PO3N](4-) ions. The crystal structures were elucidated by single-crystal X-ray diffraction. Sr2PO3N [space group Pnma (No. 62), Z = 4, a = 7.1519(5) Å, b = 5.5778(3) Å, c = 9.8132(7) Å, R1 = 0.020, wR2 = 0.047] crystallizes in the β-K2SO4 structure type. The structure of Ca2PO3N was solved and refined in the (3 + 1)D superspace group Pnma(α00)0ss [Z = 4, a = 6.7942(7) Å, b = 5.4392(6) Å, c = 9.4158(11) Å, R1 = 0.041, wR2 = 0.067]. It exhibits an incommensurate modulation along [100] with a modulation vector q = [0.287(5), 0, 0]. Rietveld refinements support the structural models as well as the phase purity of the products. Upon doping with Eu(2+), Ca2PO3N exhibits luminescence in the green range (λem = 525 nm) of the visible spectrum if excited by near-UV light (λexc = 400 nm).

The oxonitridosilicate chloride La6Ba3[Si17N29O2]Cl was synthesized by a high-temperature reaction in a radiofrequency furnace starting from LaCl3, BaH2, and the ammonolysis product of Si2Cl6. Diffraction data of a micrometer-sized single crystal were obtained using microfocused synchrotron radiation at beamline ID11 of the ESRF. EDX measurements on the same crystal confirm the chemical composition. The crystal structure [space group P63/m (no. 176), a = 9.8117(14), c = 19.286(6) Å, Z = 2] contains an unprecedented interrupted three-dimensional network of vertex-sharing SiN4 and SiN3O tetrahedra. The SiN4 tetrahedra form dreier rings. Twenty of the latter condense in a way that the Si atoms form icosahedra. Each icosahedron is connected to others via six SiN4 tetrahedra that are part of dreier rings and via six Q(3)-type SiN3O tetrahedra. Rietveld refinements confirm that the final product contains only a small amount of impurities. Lattice energy (MAPLE) and bond-valence sum (BVS) calculations show that the structure is electrostatically well balanced. Infrared spectroscopy confirms the absence of N-H bonds.

A new polymorph of phosphorus nitride imide HP4N7 has been synthesized under high-pressure/high-temperature conditions from P3N5 and NH4Cl at 6 GPa and temperatures between 800 and 1300 °C. Its crystal structure was elucidated using single-crystal X-ray diffraction data. β-HP4N7 (space group C2/c, no. 15, Z = 4, a = 12.873(2) Å, b = 4.6587(4) Å, c = 8.3222(8) Å, β = 102.351(3)°, R1 = 0.0485, wR2 = 0.1083) crystallizes in a new framework structure type that is made up of all-side vertex-sharing PN4 tetrahedra. The topology of the network is represented by the point symbol (3(2).4(2).5(2).6(3).7)(3(4).4(4).5(4).6(3)), and it has not been identified in other compounds so far. Structural differences between the two polymorphs of HP4N7 as well as the topological relationship to the recently discovered high-pressure polymorph β-HPN2 are discussed. Additionally, FTIR and solid-state NMR spectroscopy are used to corroborate the results of the structure determination.

Dinitrogen (N2) ligation is a common and well-characterized structural motif in bioinorganic synthesis. In solid-state chemistry, on the other hand, homonuclear dinitrogen entities as structural building units proved existence only very recently. High-pressure/high-temperature (HP/HT) syntheses have afforded a number of binary diazenides and pernitrides with [N2](2–) and [N2](4–) ions, respectively. Here, we report on the HP/HT synthesis of the first ternary diazenide. Li2Ca3[N2]3 (space group Pmma, no. 51, a = 4.7747(1), b = 13.9792(4), c = 8.0718(4) Å, Z = 4, wRp = 0.08109) was synthesized by controlled thermal decomposition of a stoichiometric mixture of lithium azide and calcium azide in a multianvil device under a pressure of 9 GPa at 1023 K. Powder X-ray diffraction analysis reveals strongly elongated N–N bond lengths of dNN = 1.34(2)–1.35(3) Å exceeding those of previously known, binary diazenides. In fact, the refined N–N distances in Li2Ca3[N2]3 would rather suggest the presence of [N2](3·–) radical ions. Also, characteristic features of the N–N stretching vibration occur at lower wavenumbers (1260–1020 cm(–1)) than in the binary phases, and these assignments are supported by first-principles phonon calculations. Ultimately, the true character of the N2 entity in Li2Ca3[N2]3 is probed by a variety of complementary techniques, including electron diffraction, electron spin resonance spectroscopy (ESR), magnetic and electric conductivity measurements, as well as density-functional theory calculations (DFT). Unequivocally, the title compound is shown to be metallic containing diazenide [N2](2–) units according to the formula (Li(+))2(Ca(2+))3([N2](2–))3·(e(–))2.

The rare case of a metal-triggered broad-band yellow emitter among inorganic-organic hybrid materials was achieved by in situ codoping of the novel imidazolate metal-organic framework ∞(3)[Ba(Im)2] with divalent europium. The emission maximum of this dense framework is in the center of the yellow gap of primary light-emitting diode phosphors. Up to 20% Eu2+ can be added to replace Ba2+ as connectivity centers without causing observable phase segregation. High-resolution energy-dispersive X-ray spectroscopy showed that incorporation of even 30% Eu2+ is possible on an atomic level, with 2-10% Eu2+ giving the peak quantum efficiency (QE = 0.32). The yellow emission can be triggered by two processes: direct excitation of Eu2+ and an antenna effect of the imidazolate linkers. The emission is fully europium-centered, involving 5d → 4f transitions, and depends on the imidazolate surroundings of the metal ions. The framework can be obtained by a solvent-free in situ approach starting from barium metal, europium metal, and a melt of imidazole in a redox reaction. Better homogeneity for the distribution of the luminescence centers was achieved by utilizing the hydrides BaH2 and EuH2 instead of the metals.

The isotypic layered oxonitridosilicates Li(14)Ln(5)[Si(11)N(19)O(5)]O(2)F(2) (Ln = Ce, Nd) have been synthesized using Li as fluxing agent and crystallize in the orthorhombic space group Pmmn (Z = 2, Li(14)Ce(5)[Si(11)N(19)O(5)]O(2)F(2): a = 17.178(3), b = 7.6500(15), c = 10.116(2) Å, R1 = 0.0409, wR2 = 0.0896; Li(14)Nd(5)[Si(11)N(19)O(5)]O(2)F(2): a = 17.126(2), b = 7.6155(15), c = 10.123(2) Å, R1 = 0.0419, wR2 = 0.0929). The silicate layers consist of dreier and sechser rings interconnected via common corners, yielding an unprecedented silicate substructure. A topostructural analysis indicates possible 1D ion migration pathways between five crystallographic independent Li positions. The specific Li-ionic conductivity and its temperature dependence were determined by impedance spectroscopy as well as DC polarization/depolarization measurements. The ionic conductivity is on the order of 5 × 10(-5) S/cm at 300 °C, while the activation energy is 0.69 eV. Further adjustments of the defect chemistry (e.g., through doping) can make these compounds interesting candidates for novel oxonitridosilicate based ion conductors.

The alkaline earth diazenides M(AE)N(2) with M(AE) = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at high-pressure/high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wR(p) = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN(2) and BaN(2). Accordingly, CaN(2) is isotypic with SrN(2) (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wR(p) = 0.057) and the corresponding alkaline earth acetylenides (M(AE)C(2)) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN(2) adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wR(p) = 0.049). The N-N bond lengths of 1.202(4) Å in CaN(2) (SrN(2) 1.239(4) Å, BaN(2) 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N(2)](2-). Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides M(AE(2))N (M(AE) = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm(-1) assigned to the N-N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides.

A novel oxonitridophosphate, Ba(19)P(36)O(6+x)N(66-x)Cl(8+x) (x ≈ 4.54), has been synthesized by heating a multicomponent reactant mixture consisting of phosphoryl triamide OP(NH(2))(3), thiophosphoryl triamide SP(NH(2))(3), BaS, and NH(4)Cl enclosed in an evacuated and sealed silica glass ampule up to 750 °C. Despite the presence of side phases, the crystal structure was elucidated ab initio from high-resolution synchrotron powder diffraction data (λ = 39.998 pm) applying the charge flipping algorithm supported by independent symmetry information derived from electron diffraction (ED) and scanning transmission electron microscopy (STEM). The compound crystallizes in the cubic space group Fm ̅3c (no. 226) with a = 2685.41(3) pm and Z = 8. As confirmed by Rietveld refinement, the structure comprises all-side vertex sharing P(O,N)(4) tetrahedra forming slightly distorted 3(8)4(6)8(12) cages representing a novel composite building unit (CBU). Interlinked through their 4-rings and additional 3-rings, the cages build up a 3D network with a framework density FD = 14.87 T/1000 Å(3) and a 3D 8-ring channel system. Ba(2+) and Cl(-) as extra-framework ions are located within the cages and channels of the framework. The structural model is corroborated by (31)P double-quantum (DQ) /single-quantum (SQ) and triple-quantum (TQ) /single-quantum (SQ) 2D correlation MAS NMR spectroscopy. According to (31)P{(1)H} C-REDOR NMR measurements, the H content is less than one H atom per unit cell., (© 2011 American Chemical Society)

High-pressure synthesis allows both fundamental and materials science research to gain unprecedented insight into the inner nature of materials properties at extreme environment conditions. Here, we report on the high-pressure synthesis and characterization of γ-Ca(3)N(2) and the high-pressure behavior of Mg(3)N(2). Investigation of M(3)N(2) (M = Ca, Mg) at high-pressure has been quite challenging due to the high reactivity of these compounds. Ex situ experiments have been performed using a multianvil press at pressures from 8 to 18 GPa (1000-1200 °C). Additional in situ experiments from 0 to 6 GPa (at RT) at the multianvil press MAX 80 (HASYLAB, Beamline F.2.1, Hamburg) have been carried out. The new cubic high-pressure phase γ-Ca(3)N(2) with anti-Th(3)P(4) defect structure exhibits a significant increase in coordination numbers compared to α-Ca(3)N(2). Contrary, Mg(3)N(2) shows decomposition starting at surprisingly low pressures, thereby acting as a precursor for Mg nanoparticle formation with bcc structure. Soft X-ray spectroscopy in conjunction with first principles DFT calculations have been used to explore the electronic structure and show that γ-Ca(3)N(2) is a semiconductor with inherent nitrogen vacancies.

The mixed valence europium nitridosilicate Eu(2)SiN(3) has been synthesized at 900 degrees C in welded tantalum ampules starting from europium and silicon diimide Si(NH)(2) in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a = 542.3(11) pm, b = 1061.0(2) pm, c = 1162.9(2) pm, Z = 8, 767 independent reflections, 37 parameters, R1 = 0.017, wR2 = 0.032). Eu(2)SiN(3) is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN(4) tetrahedra running parallel [100] with a maximum stretching factor f(s) = 1.0. The compound is isostructural with Ca(2)PN(3) and Rb(2)TiO(3), and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu(2+) and Eu(3+), respectively. (151)Eu Mössbauer spectroscopy of Eu(2)SiN(3) differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu(2+) and Eu(3+) signals over the whole temperature range. The Eu(2+) site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie-Weiss behavior above 24 K with an effective magnetic moment of 7.5 mu(B)/f.u. and a small contribution of Eu(3+), in accordance with Eu(2+) and Eu(3+) in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at T(C) = 24 K. DFT calculations of Eu(2)SiN(3) reveal a band gap of approximately 0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu(2+) and Eu(3+).

The alkaline earth nitridogermanate nitrides AE(7)[GeN(4)]N(2) (AE = Ca, Sr) have been synthesized using a Na flux technique in sealed Ta tubes. According to single-crystal X-ray diffraction the isotypic compounds crystallize in space group Pbcn (No. 60) with Z = 4, (Sr(7)[GeN(4)]N(2): a = 1152.6(2), b = 658.66(13), c = 1383.6(3) pm, V = 1050.5(4) x 10(6) pm(3), R1 = 0.049; Ca(7)[GeN(4)]N(2): a = 1082.6(2), b = 619.40(12), c = 1312.1(3) pm, V = 879.8(3) x 10(6) pm(3), R1 = 0.016). Owing to the high N/Ge ratio, the compounds contain discrete N(3-) ions coordinated by six AE(2+) besides discrete [GeN(4)](8-) tetrahedrons. One of the AE(2+) ion is coordinated by only four N(3-) ions, which is rather an unusual low coordination number for Sr(2+). Together with the isolated [GeN(4)](8-) tetrahedrons, these Sr(2+) ions form chains of alternating cation centered edge sharing tetrahedrons. The electronic structure and chemical bonding in Sr(7)[GeN(4)]N(2) has been analyzed employing linear muffin-tin orbital (LMTO) band structure calculations.

The reorientational dynamics of ammonium dicyanamide ND4[N(C[triple bond]N)2] and the kinetics as well as the mechanism of the solid-state isomerization reaction from ammonium dicyanamide into dicyandiamide (N[triple bond]C-N==C(NH2)2) was studied by means of 2H and 14N solid-state NMR spectroscopy in a temperature range between 38 and 390 K. Whereas in previous investigations the mechanism of the solid-state transformation was investigated by means of vibrational and magic angle spinning solid-state NMR spectroscopy as well as neutron diffraction, we here present a comprehensive 2H study of the ammonium ion dynamics prior to and during the course of the reaction, thereby highlighting possible cross correlations between dynamics and reactivity involving the ammonium ion. The ND4+ group was found to undergo thermally activated random jumps in a tetrahedral potential, which is increasingly distorted with increasing temperature, giving rise to an asymmetrically compressed or elongated tetrahedron with deviations from the tetrahedral angle of up to 6 degrees . The correlation time follows an Arrhenius law with an activation energy of Ea = 25.8(2) kJ mol(-1) and an attempt frequency of tau0(-1) = 440(80) THz. The spin-lattice relaxation times were fitted according to a simple Bloembergen-Purcell-Pound type model with a T1 minimum of 4 ms at 230 K. Temperature-dependent librational amplitudes were extracted by line-shape simulations between 38 and 390 K and contrasted with those obtained by neutron diffraction, their values ranging between 5 and 28 degrees . The onset and progress of the solid-phase transformation were followed in situ at temperatures above 372 K and could be classified as a strongly temperature-dependent, heterogeneous two-step reaction proceeding with rapid evolution of ammonia and comparatively slow subsequent reintegration into the solid. On the microscopic level, this correlates with a rapid proton transfer -- possibly triggered by a coupling between the ammonium ion dynamics and phonon modes on the terahertz time scale -- and an essentially decoupled nucleophilic attack of ammonia at the nitrile carbon, giving rise to significantly differing time constants for the two processes.

The mechanism of the solid-solid transformation of NH(4)[N(CN)(2)] into NCN[double bond]C(NH(2))(2), which represents the isolobal analogue of Wöhler's historic conversion of ammonium cyanate into urea, has been investigated by temperature-dependent single-crystal and powder X-ray diffraction, neutron powder diffraction, and Raman and solid-state NMR spectroscopy as well as thermoanalytical measurements. The transformation of the ionic dicyanamide into its molecular isomer upon controlled thermal treatment was found to proceed topochemically in the solid state with little molecular motion, giving rise to a single-crystal to single-crystal transformation which manifests itself by a defined metric relation between the unit cells of the two isomers. The exothermic phase transition is thermally activated and was observed to commence at temperatures > or =80 degrees C. The pronounced temperature dependence of the onset of the transformation may be assessed as an indication for the metastability of ammonium dicyanamide at elevated temperatures. Thermal analyses reveal a decrease in the reaction enthalpy (56-13 kJ mol(-1)) at higher heating rates and an average mass loss of 10% gaseous ammonia. Evidence was found for crucial mechanistic steps of the transformation, which is likely to proceed via proton transfer from the ammonium ion to one of the terminal nitrogen atoms of the anion. The protonation is followed by nucleophilic attack of the in situ generated ammonia at the electrophilic nitrile carbon. The proposed mechanistic pathway is based on the results of combined Raman and solid-state NMR spectroscopic as well as neutron powder diffraction measurements.

Single-phase melem (2,5,8-triamino-tri-s-triazine) C(6)N(7)(NH(2))(3) was obtained as a crystalline powder by thermal treatment of different less condensed C-N-H compounds (e.g., melamine C(3)N(3)(NH(2))(3), dicyandiamide H(4)C(2)N(4), ammonium dicyanamide NH(4)[N(CN)(2)], or cyanamide H(2)CN(2), respectively) at temperatures up to 450 degrees C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu K alpha(1): P2(1)/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, beta = 99.912(2) degrees, and Z = 4). In the solid, melem consists of nearly planar C(6)N(7)(NH(2))(3) molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed (13)C and (15)N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectroscopy. The structural and vibrational properties of molecular melem were theoretically studied on both the B3LYP and the MP2 level. A structural optimization in the extended state was performed employing density functional methods utilizing LDA and GGA. A good agreement was found between the observed and calculated structural parameters and also for the vibrational frequencies of melem. According to temperature-dependent X-ray powder diffractometry investigations above 560 degrees C, melem transforms into a graphite-like C-N material.

Ammonium dicyanamide NH(4)[N(CN)(2)] was synthesized through aqueous ion exchange. The crystal structure was investigated by single-crystal X-ray diffraction (P2(1)/c, a = 378.67(6) pm, b = 1240.9(3) pm, c = 911.84(14) pm, beta = 91.488(18) degrees, Z = 4). It derives from the CsCl structure type. Medium strong hydrogen bonds between NH(4)(+) and [N(CN)(2)](-) ions are indicative of the observed formation of dicyandiamide H(4)C(2)N(4) during heating. According to DSC and temperature-dependent X-ray powder diffractometry, this isomerization is exothermic and occurs between 102 and 106 degrees C in the solid. The reaction represents the isolobal analogue to the classical synthesis of urea by heating NH(4)OCN. While other alkali and alkaline earth dicyanamides undergo trimerization or polymerization of their anions during heating, ammonium dicyanamide thus shows a different reactivity.

The Lewis acid-base adducts (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) and (P(4)Se(3)).(NbCl(5)) have been prepared and characterized by Raman, IR, and solid-state (31)P MAS NMR spectroscopy. Hybrid density functional calculations (B3LYP) have been carried out for both the apical and the basal (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) adducts. The thermodynamics of all considered species has been discussed. In accordance with solid-state (31)P MAS NMR and vibrational data, the X-ray powder diffraction structures of (P(4)S(3)).(BBr(3)) [monoclinic, space group P2(1)/m (No. 11), a = 8.8854(1) A, b = 10.6164(2) A, c = 6.3682(1) A, beta = 108.912(1) degrees, V = 568.29(2) A(3), Z = 2] and (P(4)S(3)).(BI(3)) [orthorhombic, space group Pnma (No. 62), a = 12.5039(5) A, b = 11.3388(5) A, c = 8.9298(4) A, V = 1266.09(9) A(3), Z = 4] indicate the formation of an apical P(4)S(3) complex in the reaction of P(4)S(3) with BX(3) (X = Br, I). Basal adducts are formed when P(4)Se(3) is used as the donor species. Vibrational assignment for the normal modes of these adducts has been made on the basis of comparison between theoretically obtained and experimentally observed vibrational data.

Sodium dicyanamide NaC2N3 was found to undergo two phase transitions. According to thermal analysis and temperature-dependent X-ray powder diffractometry, the transition of alpha-NaC2N3 (1a) to beta-NaC2N3 (1b) occurs at 33 degrees C and is displacive. 1a crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 647.7(1), b = 1494.8(3), c = 357.25(7) pm, beta = 93.496(1) degrees, and Z = 4. The structure was solved from powder diffraction data (Cu Kalpha1, T = 22 degrees C) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.072, Rp = 0.053, and RF = 0.074. 1b crystallizes in the orthorhombic system, space group Pbnm (no. 62), with a = 650.15(5), b = 1495.1(2), c = 360.50(3) pm, and Z = 4. The structure was refined by the Rietveld method using the atomic coordinates of 1a as starting values (Mo Kalpha1, T = 150 degrees C). The final agreement factors were wRp = 0.044, Rp = 0.034, RF = 0.140. The crystal structures of both polymorphs contain sheets of Na+ and N(CN)2- ions which are in la nearly and in 1b exactly coplanar. Above 340 degrees C, 1b trimerizes in the solid to Na3C6N9 (2). 2 crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 1104.82(1), b = 2338.06(3), c = 351.616(3) pm, beta = 97.9132(9)degrees, and Z = 4. The structure was solved from synchrotron powder diffraction data (lambda = 59.733 pm) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.080, Rp = 0.059, and RF = 0.080. The compound contains Na+ and the planar tricyanomelaminate C6N9(3-). The phase transition from 1b to 2 is reconstructive. It occurs in the solid-state without involvement of other phases or intermediates. The crystal structures of 1b and 2 indicate that there is no preorientation of the N(CN)2- in the solid before their trimerization to C6N9(3-).