Single-phase melem (2,5,8-triamino-tri-s-triazine) C6N7(NH2)3 was obtained as a crystalline powder by thermal treatment of different less condensed C-N-H compounds (e.g., melamine C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH4[N(CN)2], or cyanamide H2CN2, respectively) at temperatures up to 450°C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu KR1: P21/c (No. 14), a ) 739.92(1) pm, b ) 865.28(3) pm, c ) 1338.16(4) pm, ) 99.912(2)°, and Z ) 4). In the solid, melem consists of nearly planar C6N7(NH2)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°C, melem transforms into a graphite-like C-N material.Melamine (2,4,6-triamino-s-triazine), C 3 N 3 (NH 2 ) 3 1a, represents an important starting material for several industrial applications, for example, the syntheses of melamine-formaldehyde resins or of fireproof materials. 1,2 Furthermore, it is used for the architecture of supramolecular structures, for example, assemblies built up by cyanuric acid C 3 N 3 (OH) 3 1b or melamine derivatives. [3][4][5] In the past few years, another interest arose in melamine as well as in other compounds, C 3 N 3 X 3 1, containing s-triazine (cyanuric) rings C 3 N 3 , for example, cyanuric chloride C 3 N 3 Cl 3 1c [6][7][8][9][10] or cyanuric azide C 3 N 3 (N 3 ) 3 1d. 11 These are considered to be suitable molecular precursor compounds for the synthesis of graphitic forms of carbon nitride (g-C 3 N 4 ). 6,[12][13][14] In most of the postulated structures of g-C 3 N 4 , s-triazine ring systems are linked through trigonal N atoms forming extended 2D sheets 2 (Scheme 1).Recently, another possible building block for g-C 3 N 4 was taken into account (Scheme 2): tri-s-triazine rings C 6 N 7 which are cross-linked by trigonal N atoms 3. [15][16][17] The possible condensation of three s-triazine rings and the existence of a "cyameluric nucleus" C 6 N 7 4 was first postulated by Pauling † Ludwig-Maximilians-Universität München.

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Gauge including projector augmented wave (GIPAW) NMR calculations combined with hybrid Monte Carlo/ molecular dynamics simulations are carried out in order to investigate the relationships between the oxygen-17 and silicon-29 NMR spectra of vitreous silica and its local structure in terms of the Si-O-Si bond angle and Si-O distance distributions. Special attention is paid to the structure and NMR parameters of three-and four-membered rings, and the effect of their concentration on glass density is studied. It is shown that our simulations provide a new insight into the features of the 17 O NMR parameters distribution. Accordingly, a new analytical model is presented and applied for the reconstruction of the Si-O-Si angle from the NMR spectrum. The reliability of the procedure is demonstrated conclusively through the excellent consistency of the analysis of the oxygen-17 and silicon-29 NMR experimental data of vitreous silica. Si-O-Si angle distribution mean values of 147.1°and 148.4°, respectively, and standard deviations of 11.2°and 10.8°, respectively, are obtained from the oxygen-17 and silicon-29 NMR experimental spectrum (Clark et al., ref 4) of the same sample.

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The magnetism in graphene due to single-atom defects is examined by using spin-polarized density functional theory. The magnetic moment per defect due to substitutional atoms and vacancy defects is dependent on the density of defects, while that due to adatom defects is independent of the density of defects. It reduces to zero with decrease in the density of substitutional atoms. However, it increases with decrease in density of vacancies. The graphene sheet with B adatoms is nonmagnetic, but with C and N adatoms it is magnetic. The adatom defects distort the graphene sheet near the defect perpendicular to the sheet. The distortion in graphene due to C and N adatoms is significant, while the distortion due to B adatoms is very small. The vacancy and substitutional atom (B, N) defects in graphene are planar in the sense that there is in-plane displacement of C atoms near the vacancy and substitutional defects. Upon relaxation the displacement of C atoms and the formation of pentagons near the vacancy site due to Jahn-Teller distortion depends upon the density and packing geometry of vacancies.

A series of thermally stable, easily isolable, monomeric, and isoleptic coinage metal alkyne complexes have been reported. Treatment of [N{(C(3)F(7))C(Dipp)N}(2)]Li (the lithium salt of the 1,3,5-triazapentadiene [N{(C(3)F(7))C(Dipp)N}(2)]H) with AuCl, CF(3)SO(3)Ag or CF(3)SO(3)Cu in the presence of 3-hexyne led to the corresponding coinage metal alkyne complex [N{(C(3)F(7))C(Dipp)N}(2)]M(EtC[triple bond]CEt) in good yield (M = Au, Ag, Cu; Dipp = 2,6-diisopropylphenyl). X-ray crystal structures of the three coinage metal alkynes are remarkably similar, and show the presence of trigonal-planar metal sites with eta(2)-bonded 3-hexyne. The M-C and M-N bond distances vary in the order Cu < Au < Ag. The bending of the C-C[triple bond]C bond angle is largest for the gold, followed by Cu and Ag adducts. The gold adduct also shows the largest decrease in C[triple bond]C stretching frequency in Raman, while the Ag adduct shows the smallest change compared to that of the uncoordinated alkyne. DFT calculations on [N{(CF(3))C(Ph)N}(2)]M(EtC[triple bond]CEt) and the related ClM(EtC[triple bond]CEt) predict that the M-alkyne bond energy varies in the order Ag < Cu < Au. The gold adducts are also predicted to have the longest C[triple bond]C, largest deviation of C-C[triple bond]C bond angle from linearity, and smallest C[triple bond]C stretching frequency, followed by the Cu and Ag adducts. In these triazapentadienyl coinage metal adducts, the sigma-donation from alkyne --> M dominates over the M --> alkyne pi-back-donation.

Besides temperature at one atmosphere, the applied pressure is another important parameter for influencing and controlling reaction pathways and final reaction products. This is relevant not only for the genesis of natural minerals, but also for synthetic chemical products and technological materials. The present critical review (316 references) highlights recent developments that utilise high pressures and high-temperatures for the synthesis of new materials with unique properties, such as high hardness, or interesting magnetic or optoelectronic features. Novel metal nitrides, oxonitrides as well as the new class of nitride-diazenide compounds, all formed under high-pressure conditions, are highlighted. Pure oxides and carbides are not considered here. Moreover, syntheses under high-pressure conditions require special equipment and preparation techniques, completely different from those used for conventional synthetic approaches at ambient pressure. Therefore, we also summarize the high-pressure techniques used for the synthesis of new materials on a laboratory scale. In particular, our attention is focused on reactive gas pressure devices with pressures between 1.2 and 600 MPa, multi-anvil apparatus at P < 25 GPa and the diamond anvil cell, which allows work at pressures of 100 GPa and higher. For example, some of these techniques have been successfully upgraded to an industrial scale for the synthesis of diamond and cubic boron nitride.