High-pressure silicates making up the main proportion of the earth's interior can incorporate a significant amount of water in the form of OH defects. Generally, they are charge balanced by removing low-valent cations such as Mg. By combining high-resolution multidimensional single- and double-quantum H solid-state NMR spectroscopy with density functional theory calculations, we show that, for ringwoodite (γ-MgSiO), additionally, Si vacancies are formed, even at a water content as low as 0.1 wt %. They are charge balanced by either four protons or one Mg and two protons. Surprisingly, also a significant proportion of coupled Mg and Si vacancies are present. Furthermore, all defect types feature a pronounced orientational disorder of the OH groups, which results in a significant range of OH···O bond distributions. As such, we are able to present unique insight into the defect chemistry of ringwoodite's spinel structure, which not only accounts for a potentially large fraction of the earth's entire water budget, but will also control transport properties in the mantle. We expect that our results will even impact other hydrous spinel-type materials, helping to understand properties such as ion conduction and heterogeneous catalysis.

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In this work, trimethoxyboroxine (TMB) is identified as a small-molecule glass former. In its viscous liquid as well as glassy states, static and dynamic properties of TMB are explored using various techniques. It is found that, on average, the structure of the condensed TMB molecules deviates from threefold symmetry so that TMB’s electric dipole moment is nonzero, thus rendering broadband dielectric spectroscopy applicable. This method reveals the super-Arrhenius dynamics that characterizes TMB above its glass transition, which occurs at about 204 K. To extend the temperature range in which the molecular dynamics can be studied, 11B nuclear magnetic resonance experiments are additionally carried out on rotating and stationary samples: Exploiting dynamic second-order shifts, spin-relaxation times, line shape effects, as well as stimulated-echo and two-dimensional exchange spectroscopy, a coherent picture regarding the dynamics of this glass former is gained.

Abstract.A so far unknown third polymorph (form III) of 5-amino-2,3-dihydro-1,4-phthalazinedione (luminolate) monosodium salt could be isolated phase pure and its structure was determined by powder X-ray diffraction and Rietveld refinement [cell parameters: a = 8.0364(2) Å, b = 3.69765(5) Å, c = 26.4246(7) Å, β = 96.346(2)°, V = 780.42(3) Å 3 , space group P2 1 /c]. The new structure shows many similarities to the structure of the known form II and the consequently slim differences in the diffraction traces could have easily been over-