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Abstract Bridgmanite, the most abundant mineral in the lower mantle, can play an essential role in deep-Earth hydrogen storage and circulation processes. To better evaluate the hydrogen storage capacity and its substitution mechanism in bridgmanite occurring in nature, we have synthesized high-quality single-crystal bridgmanite with a composition of (Mg0.88Fe0.052+Fe0.053+Al0.03)(Si0.88Al0.11H0.01)O3 at nearly water-saturated environments relevant to topmost lower mantle pressure and temperature conditions. The crystallographic site position of hydrogen in the synthetic (Fe,Al)-bearing bridgmanite is evaluated by a time-of-flight single-crystal neutron diffraction scheme, together with supporting evidence from polarized infrared spectroscopy. Analysis of the results shows that the primary hydrogen site has an OH bond direction nearly parallel to the crystallographic b axis of the orthorhombic bridgmanite lattice, where hydrogen is located along the line between two oxygen anions to form a straight geometry of covalent and hydrogen bonds. Our modeled results show that hydrogen is incorporated into the crystal structure via coupled substitution of Al3+ and H+ simultaneously exchanging for Si4+, which does not require any cation vacancy. The concentration of hydrogen evaluated by secondary-ion mass spectrometry and neutron diffraction is ~0.1 wt% H2O and consistent with each other, showing that neutron diffraction can be an alternative quantitative means for the characterization of trace amounts of hydrogen and its site occupancy in nominally anhydrous minerals. 

Diffuse scattering occurring in the Bragg diffraction pattern of a long-range-ordered structure represents local deviation from the governing regular lattice. However, interpreting the real-space structure from the diffraction pattern presents a significant challenge because of the dramatic difference in intensity between the Bragg and diffuse components of the total scattering function. In contrast to the sharp Bragg diffraction, the diffuse signal has generally been considered to be a weak expansive or continuous background signal. Herein, using 1D and 2D models, it is demonstrated that diffuse scattering in fact consists of a complex array of high-frequency features that must not be averaged into a low-frequency background signal. To evaluate the actual diffuse scattering effectively, an algorithm has been developed that uses robust statistics and traditional signal processing techniques to identify Bragg peaks as signal outliers which can be removed from the overall scattering data and then replaced by statistically valid fill values. This method, described as a `K-space algorithmic reconstruction' (KAREN), can identify Bragg reflections independent of prior knowledge of a system's unit cell. KAREN does not alter any data other than that in the immediate vicinity of the Bragg reflections, and reconstructs the diffuse component surrounding the Bragg peaks without introducing discontinuities which induce Fourier ripples or artifacts from underfilling `punched' voids. The KAREN algorithm for reconstructing diffuse scattering provides demonstrably better resolution than can be obtained from previously described punch-and-fill methods. The superior structural resolution obtained using the KAREN method is demonstrated by evaluating the complex ordered diffuse scattering observed from the neutron diffraction of a single plastic crystal of CBr 4 using pair distribution function analysis. 

Understanding H 2 binding and activation is important in the context of designing transition metal catalysts for many processes, including hydrogenation and the interconversion of H 2 with protons and electrons. This work reports the first thermodynamic and kinetic H 2 binding studies for an isostructural series of first-row metal complexes: NiML, where M = Al ( 1 ), Ga ( 2 ), and In ( 3 ), and L = [N( o -(NCH 2 P i Pr 2 )C 6 H 4 ) 3 ] 3− . Thermodynamic free energies (Δ G °) and free energies of activation (Δ G ‡ ) for binding equilibria were obtained via variable-temperature 31 P NMR studies and lineshape analysis. The supporting metal exerts a large influence on the thermodynamic favorability of both H 2 and N 2 binding to Ni, with Δ G ° values for H 2 binding found to span nearly the entire range of previous reports. The non-classical H 2 adduct, (η 2 -H 2 )NiInL ( 3 -H 2 ), was structurally characterized by single-crystal neutron diffraction—the first such study for a Ni(η 2 -H 2 ) complex or any d 10 M(η 2 -H 2 ) complex. UV-Vis studies and TD-DFT calculations identified specific electronic structure perturbations of the supporting metal which poise NiML complexes for small-molecule binding. ETS-NOCV calculations indicate that H 2 binding primarily occurs via H–H σ-donation to the Ni 4p z -based LUMO, which is proposed to become energetically accessible as the Ni(0)→M( iii ) dative interaction increases for the larger M( iii ) ions. Linear free-energy relationships are discussed, with the activation barrier for H 2 binding (Δ G ‡ ) found to decrease proportionally for more thermodynamically favorable equilibria. The Δ G ° values for H 2 and N 2 binding to NiML complexes were also found to be more exergonic for the larger M( iii ) ions.