Poly(aminoimino)heptazine, otherwise known as Liebig's melon, whose composition and structure has been subject to multitudinous speculations, was synthesized from melamine at 630 degrees C under the pressure of ammonia. Electron diffraction, solid-state NMR spectroscopy, and theoretical calculations revealed that the nanocrystalline material exhibits domains well-ordered in two dimensions, thereby allowing the structure solution in projection by electron diffraction. Melon ([C(6)N(7)(NH(2))(NH)](n), plane group p2 gg, a=16.7, b=12.4 A, gamma=90 degrees, Z=4), is composed of layers made up from infinite 1D chains of NH-bridged melem (C(6)N(7)(NH(2))(3)) monomers. The strands adopt a zigzag-type geometry and are tightly linked by hydrogen bonds to give a 2D planar array. The inter-layer distance was determined to be 3.2 A from X-ray powder diffraction. The presence of heptazine building blocks, as well as NH and NH(2) groups was confirmed by (13)C and (15)N solid-state NMR spectroscopy using (15)N-labeled melon. The degree of condensation of the heptazine core was further substantiated by a (15)N direct excitation measurement. Magnetization exchange observed between all (15)N nuclei using a fp-RFDR experiment, together with the CP-MAS data and elemental analysis, suggests that the sample is mainly homogeneous in terms of its basic composition and molecular building blocks. Semiempirical, force field, and DFT/plane wave calculations under periodic boundary conditions corroborate the structure model obtained by electron diffraction. The overall planarity of the layers is confirmed and a good agreement is obtained between the experimental and calculated NMR chemical shift parameters. The polymeric character and thermal stability of melon might render this polymer a pre-stage of g-C(3)N(4) and portend its use as a promising inert material for a variety of applications in materials and surface science.

The gas-phase loading of [Zn(4)O(btb)(2)](8) (MOF-177; H(3)btb=1,3,5-benzenetribenzoic acid) with the volatile platinum precursor [Me(3)PtCp'] (Cp'=methylcyclopentadienyl) was confirmed by solid state (13)C magic angle spinning (MAS)-NMR spectroscopy. Subsequent reduction of the inclusion compound [Me(3)PtCp'](4)@MOF-177 by hydrogen at 100 bar and 100 degrees C for 24 h was carried out and gave rise to the formation of platinum nanoparticles in a size regime of 2-5 nm embedded in the unchanged MOF-177 host lattice as confirmed by transmission electron microscopy (TEM) micrographs and powder X-ray diffraction (PXRD). The room-temperature hydrogen adsorption of Pt@MOF-177 has been followed in a gravimetric fashion (magnetic suspension balance) and shows almost 2.5 wt % in the first cycle, but is decreased down to 0.5 wt % in consecutive cycles. The catalytic activity of Pt@MOF-177 towards the solvent- and base-free room temperature oxidation of alcohols in air has been tested and shows Pt@MOF-177 to be an efficient catalyst in the oxidation of alcohols.

SrP2N4 was obtained by high-pressure high-temperature synthesis utilizing the multianvil technique (5 GPa, 1400 degrees C) starting from mixtures of phosphorus(V) nitride and strontium azide. SrP2N4 turned out to be isotypic with BaGa(2)O(4) and is closely related to KGeAlO(4). The crystal structure (SrP2N4, a=17.1029(8), c=8.10318(5) A, space group P6(3) (no. 173), V=2052.70(2) A3, Z=24, R(F2)=0.0633) was solved from synchrotron powder diffraction data by applying a combination of direct methods, Patterson syntheses, and difference Fourier maps adding the unit cell information derived from electron diffraction and symmetry information obtained from 31P solid-state NMR spectroscopy. The structure of SrP2N4 was refined by the Rietveld method by utilizing both neutron and synchrotron X-ray powder diffraction data, and has been corroborated additionally by 31P solid-state NMR spectroscopy by employing through-bond connectivities and distance relations.

One hundred seventy-five years ago, Friedrich Wöhler and Justus von Liebig described the first incidence of polymorphism with a molecular crystal.[1] Today thermodynamic and kinetic factors associated with polymorphism still represent major challenges in solid-state research. Despite the pronounced impact of polymorphism [2] on physical and chemical properties (e.g. solubility, shelf life) and the legal and economic implications resulting from these differences (see the case of Ritonavir [3,4] ), the deliberate and reproducible synthesis of metastable polymorphs from solution remains difficult and is far from trivial. It entails controlling the nucleation of the desired form as well as simultaneously suppressing nucleation of competing congeners. If secondary nucleation cannot be prevented, the metastable form will be transformed by dissolution and reprecipitation into the more stable form. The difference in lattice energy and hence solubility is the driving force for the transformation. Large differences will render metastable forms transient and difficult to capture. [5] By chance, the very first known molecular dimorph, benzamide, appeared to form crystals with metastable modifications. Wöhler and Liebig described that slow cooling of a "boiling hot" aqueous solution of benzamide resulted in a white mass of silky needles. After a few hours or days they observed a phase transformation in solution towards wellformed rhombic crystals. This stable monoclinic form (form I) was thoroughly investigated, and the crystal structure was solved in 1959 by single-crystal X-ray diffraction.[6] The metastable form was forgotten for over 150 years, and the existence of this second phase was referred to only in passing. [7] No crystal structure was available-a rather ominous fact for a simple molecule with limited torsional flexibility. In 2005 David et al. solved the structure of a new metastable polymorph (form II) from X-ray powder diffraction data [8] that were rapidly recorded (< 60 min.) at a synchrotron source. The crystals of form II were obtained in situ on the diffractometer by cooling a dilute solution (0.173 m) in a flame-sealed glass capillary (1.5 mm). Initially the solution was cooled to 2 8C followed by flash cooling "through brief contact with a cotton bud soaked in liquid nitrogen". In this way the relative proportion of form II over form I could be increased to a maximum of 17.3 %. Please note that these crystallization conditions deviate dramatically from those in the original experiment described by Wöhler and Liebig. In a subsequent full paper Bladgen et al. showed that the solid-state transformation of the highly metastable form II into form I is facile and complete within 3 h. [9] We repeated the original experiment in an automated lab reactor (LabMax, Mettler Toledo) equipped with online sensors that afford more controlled crystallization conditions. The saturation level was monitored with an ATR FT-IR probe (ReactIR, Mettler Toledo), and a FBRM probe (focused beam reflectance measurement, Lasentech) d...

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