Symmetry Of Center Research Articles

Template‐Sacrificing Synthesis of Asymmetrically Coordinated Zn Single‐Atom Sites for High‐Performance Sodium–Sulfur Batteries

AbstractMetal single‐atom catalysts (SACs) are extensively investigated to accelerate the sulfur redox kinetics in room‐temperature sodium─sulfur (Na─S) batteries. Nevertheless, the influence of the structure symmetry of SACs center on the electrocatalytic mechanism and the precise pathway in which single‐atom active sites facilitate sodium polysulfides (Na2Sn) conversion remain unknown. To enable controlled construction of highly active single‐atom configuration, herein, Zn SACs with an asymmetrical Zn─N3O configuration are designed for sodium polysulfides conversion. Both theoretical and experimental explorations reveal that the Zn─N3O single‐atom center displays higher electrocatalytic activity for polysulfides conversion than the Zn─N4 single‐atom center. The N/O co‐coordination induces the localized charge at Zn single‐atom center, which strengthens the d‐p hybridization with Na2Sn and stretches Na─S bond length of Na2Sn, thus accelerating the sulfur redox reaction kinetics. Consequently, the as‐assembled Na─S batteries achieve a high capacity of 1016 mAh g−1 at 1.0 C with a capacity decay of 0.0186% per cycle over 1000 cycles. This work uncovers the subtle relationship between the electrocatalytic activity of species conversion and the local coordination environment of SACs, and offers a guidance for the design of efficient asymmetrical SACs for different catalysis applications.

Regulating the Electronic Configuration of Ni Sites by Breaking Symmetry of Ni‐Porphyrin to Facilitate CO2 Photocatalytic Reduction

AbstractAdapting the coordination environment to influence the electronic configuration of active sites represents an efficient approach for improving the photocatalytic performance of the CO2 reduction reaction (CO2RR) but how to execute it precisely remains challenging. Herein, heteroatom‐substitution in Ni‐porphyrin to break the coordination symmetry of Ni center is proposed to be an effective solution. Based on this, two symmetry‐breaking Ni‐porphyrins, namely Ni(Cl)ON3Por and Ni(Cl)SN3Por, are designed and successfully prepared. By theoretical calculation, it is found that symmetry‐breaking efficiently regulates the 3d orbital energy levels of Ni center. Furthermore, experimental and theoretical findings jointly revealed that coordination symmetry‐breaking of Ni‐porphyrins facilitates the generation of highly reactive NiI species during the catalytic process, effectively stabilizing and reducing the energy barrier of formation of the key *COOH intermediate. As a result, Ni(Cl)ON3Por and Ni(Cl)SN3Por gave CO production rates of 24.7 and 38.8 mmol g−1 h−1 as well as selectivity toward CO of 94.0% and 96.4%, respectively, outperforming that of symmetric NiN4Por (CO production rate of 6.6 mmol g−1 h−1 and selectivity of 82.8%). These findings offer microscopic insights into how to modulate the catalytic activity by precisely tuning the coordination environment of active sites and rational design of competent catalyst for CO2RR photocatalysis.

Enhancing the magnetic properties of Dy(III) single-molecule magnets in octahedral coordination symmetry by tuning the equatorial ligands.

Conventionally, octahedral (Oh) coordination symmetry of lanthanide centers is not ideal for constructing high-performance single-molecule magnets (SMMs). However, introducing a strong ligand field in the axial direction to increase crystal field splitting can potentially overcome this limitation. Herein, we successfully obtained two dysprosium(III) single-molecule magnets, [Dy(OCtBu3)X2(py)3] (X = Cl (1), I (2), py = pyridine), in Oh coordination symmetry. The two complexes differ only in the coordinating anions on the equatorial plane, yet their magnetic performances are distinctly different. When chloride is replaced by a weaker donor iodide, the energy barrier is dramatically improved from 29 cm-1 (1) to 860 cm-1 (2), highlighting the importance of weakening the transverse ligand field and maximizing the axial ligand field for high-performance SMMs.

In English

The equilibrium and spatial structure of the polycyclic aromatic hydrocarbon C96H24, chosen as a model of the graphene plane, as well as the systems obtained from it by removing the diatomic molecule C2 (C94H24) and then replacing four carbon atoms with four nitrogen atoms (C90N4H24) have been studied by the DFT method (B3LYP) in the 6-31G** basis using Grimme corrections to account for dispersion interactions. In the same approximation, the energetics of the formation of a complex of an iron atom in zero oxidation degree (Fe0) with C90N4H24 ([C90N4H24Fe]0) in the square planar field of the ligand has been studied. The types of molecular orbitals of the ligand, which correspond to the symmetry of the atomic d-orbitals of the Fe atom, have been determined. Interaction diagrams of the d-orbitals of the Fe atom with some molecular orbitals of the ligand C90N4H24 of the corresponding symmetry are constructed. It is concluded that the binding of the transition metal atom on the double vacancy of the graphene plane can be rationally described based on the local symmetry of the coordination center and molecular orbitals of the ligand and the formed complex.

The effect of Pr3+ concentration on the microstructure, luminescence and scintillation properties of Pr:LuAG single crystals

High-quality lutetium aluminum garnet doped with various Pr3+ concentrations ((Lu1-xPrx)3Al5O12, abbreviated to Pr:LuAG) single crystals were grown by the optical floating zone method. The concentration of Pr3+ dependence on microstructure, luminescence and scintillation properties were systematically studied. Based on the results of Rietveld refinement, the doping of Pr3+ leads to lattice distortion and lowers its symmetry. The symmetry of the LuO8 dodecahedron center is lowest at 0.010, as confirmed by the Raman spectra. When excited at 450 nm and X-rays, the primary emission peak at 614 and 300 nm, respectively, induced by Pr3+ 4f2-4f2 and 4f5d-4f2 transitions. The optimal doping concentration is 0.010. The electric dipole-electric dipole interaction between adjacent Pr3+ was responsible for the concentration quenching in the Pr:LuAG single crystals. (Lu0.990Pr0.010)3Al5O12 shows the shortest average scintillation decay time (22.55 ns) and highest light yield (23,842 ± 2300 ph./MeV) under 662 KeV 137Cs gamma-ray irradiation. In terms of overall luminescence and scintillation performance, 0.010 doping was the best for Pr3+ doped LuAG single crystals.

A Symmetry Concept for the Self-Assembly Synthesis of Mn-MIL-100 Using a Capping Agent and Its Adsorption Performance with Methylene Blue

In this study, a facile strategy of regulated self-assembly synthesis of Mn-MIL-100, using sodium acetate (CH3COONa) as a mono-dentate ligand capping agent (CA), was proposed. The as-prepared product is denoted Mn-MIL-100-CA. The coordination modulation of CH3COONa, led by its interference in the connectivity and symmetry of the metal centers and organic nodes, plays a vital role in the synthesis process. The crystallinity, morphology, topology, and properties of such MOF products were improved, since the self-assembly process of Mn-MIL-100-CA was promoted and regulated effectively. The materials were systematically characterized via XRD, SEM, N2 isotherms, XPS, and TGA in terms of crystallization behavior, morphology, topology, chemical composition, and thermal and water stability. The ability of Mn-MIL-100 and Mn-MIL-100-CA to remove methylene blue (MB) from an aqueous solution was investigated using a UV–vis spectrophotometer. The results indicate that with the addition of a molar ratio of 50% CH3COONa, Mn-MIL-100-CA particles developed a regularly symmetrical morphology, i.e., ‘spherical pyramid-like structure’ crystals with a dimension of 2~5 μm. Their specific surface area and pore volume increased by 59.2% and 56.7%, respectively. The increased proportion of Mn3+ implies reduced crystal defects and improved crystal structural order and integrity, and therefore an enhanced water stability. Mn-MIL-100-CA exhibited excellent adsorption performance towards MB from aqueous solution. The equilibrium adsorption value was as high as 1079.9 mg/g, which is 44.7% higher than that of Mn-MIL-100 without the addition of CA. The good adsorption capacity and excellent water stability mean that Mn-MIL-100-CA has great potential for the practical removal of MB dye pollutants from water.

Influence of coordination environment and dielectric contrast on the spectral-luminescent properties of europium ions in the pores of film opals

The photoluminescence spectra of the inorganic salt of europium C6H9EuO6 × H2O in the pores of film opals, with globule diameter D ≈ 300 nm on a glass substrate, were measured. In the measured spectra the radiative transitions in the energy spectrum of Eu3+ 5D0→7F0, 5D0→7F1, and 5D0→7F2 were observed at wavelength 580 nm, 592 nm and 617 nm, respectively. The presence in the luminescence spectra of the maximum possible number of components of the Stark structure of the 5D0→7FJ (J=1–2) transitions, equal to 2J+1, and the high intensity of the 5D0 → 7F0 transition indicate that the symmetry of the luminescence centers is low, not higher than C3. The dependence of the luminescence spectra on the additional impregnation of the samples with glycerol was established: smoothing of the Stark structure and broadening of the 5D0→7F2 band were observed, as well as a decrease in the ratio of integrated intensities I(5D0→ 7F2 ) / I(5D0 →7F1) from 3.6 to 1.9.

Tuning Fe Spin Moment in Fe-N-C Catalysts to Climb the Activity Volcano via a Local Geometric Distortion Strategy.

As the most promising alternative to platinum-based catalysts for cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells, further performance enhancement of Fe-N-C catalysts is highly expected to promote their wide application. In Fe-N-C catalysts, the single Fe atom forms a square-planar configuration with four adjacent N atoms (D4h symmetry). Breaking the D4h symmetry of the FeN4 active center provides a new route to boost the activity of Fe-N-C catalysts. Herein, for the first time, the deformation of the square-planar coordination of FeN4 moiety achieved by introducing chalcogen oxygen groups (XO2 , X=S, Se, Te) as polar functional groups in the Fe-N-C catalyst is reported. The theoretical and experimental results demonstrate that breaking the D4h symmetry of FeN4 results in the rearrangement of Fe 3d electrons and increases spin moment of Fe centers. The efficient spin state manipulation optimizes the adsorption energetics of ORR intermediates, thereby significantly promoting the intrinsic ORR activity of Fe-N-C catalysts, among which the SeO2 modified catalyst lies around the peak of the ORR volcano plot. This work provides a new strategy to tune the local coordination and thus the electronic structure of single-atom catalysts.

Incorporation of expanded organic cations in dysprosium(III) borohydrides for achieving luminescent molecular nanomagnets

Luminescent single-molecule magnets (SMMs) constitute a class of molecular materials offering optical insight into magnetic anisotropy, magnetic switching of emission, and magnetic luminescent thermometry. They are accessible using lanthanide(III) complexes with advanced organic ligands or metalloligands. We present a simple route to luminescent SMMs realized by the insertion of well-known organic cations, tetrabutylammonium and tetraphenylphosphonium, into dysprosium(III) borohydrides, the representatives of metal borohydrides investigated due to their hydrogen storage properties. We report two novel compounds, [n-Bu4N][DyIII(BH4)4] (1) and [Ph4P][DyIII(BH4)4] (2), involving DyIII centers surrounded by four pseudo-tetrahedrally arranged BH4– ions. While 2 has higher symmetry and adopts a tetragonal unit cell (I41/a), 1 crystallizes in a less symmetric monoclinic unit cell (P21/c). They exhibit yellow room-temperature photoluminescence related to the f–f electronic transitions. Moreover, they reveal DyIII-centered magnetic anisotropy generated by the distorted arrangement of four borohydride anions. It leads to field-induced slow magnetic relaxation, well-observed for the magnetically diluted samples, [n-Bu4N][YIII0.9DyIII0.1(BH4)4] (1@Y) and [Ph4P][YIII0.9DyIII0.1(BH4)4] (2@Y). 1@Y exhibits an Orbach-type relaxation with an energy barrier of 26.4(5) K while only the onset of SMM features was found in 2@Y. The more pronounced single-ion anisotropy of DyIII complexes of 1 was confirmed by the results of the ab initio calculations performed for both 1–2 and the highly symmetrical inorganic DyIII borohydrides, α/β-Dy(BH4)3, 3 and 4. The magneto-luminescent character was achieved by the implementation of large organic cations that lower the symmetry of DyIII centers inducing single-ion anisotropy and separate them in the crystal lattice enabling the emission property. These findings are supported by the comparison with 3 and 4, crystalizing in cubic unit cells, which are not emissive and do not exhibit SMM behavior.

Cutoff for Exact Recovery of Gaussian Mixture Models

We determine the information-theoretic cutoff value on separation of cluster centers for exact recovery of cluster labels in a K-component Gaussian mixture model with equal cluster sizes. Moreover, we show that a semidefinite programming (SDP) relaxation of the K-means clustering method achieves such sharp threshold for exact recovery without assuming the symmetry of cluster centers.

Lateral Symmetry of Center of Pressure During Walking in Patients With Unilateral Knee Osteoarthritis

Background: Although symmetry of spatio-temporal parameter and center of pressure (COP) shift during walking is associated with knee adduction moment, research on clinical association with knee osteoarthritis (OA)-related knee pain and functional scores is lacking. Objects: The aims were 1) to compare symmetry of gait parameters and COP-shift in patients with unilateral knee OA and pain and matched controls, and 2) to investigate the relationship between symmetry of gait parameters and COP-shift, and clinical measures. Methods: Female subjects (n = 16) had with unilateral radiological knee OA and pain. Healthy controls (n = 15) were age-matched to OA group. Symmetry of foot rotation, step length, stance and swing phase, lateral symmetry of COP and anterior/posterior symmetry of COP during walking was assessed. To assess the clinical variables, pain intensity, pain duration and function using Knee Osteoarthritis Outcome Survey (KOOS) subscales were collected. We compared symmetry between groups using Mann–Whitney U-test or independent t-test. Relationships between clinical measures and symmetry index measured using Spearman’s correlation test. Statistical significance was set at α = 0.05. Results: Knee OA group showed significantly greater values of only lateral symmetry of COP (p < 0.01) than healthy group. Values of lateral symmetry of COP had moderate or strong correlation significantly with the intensity of knee pain, pain duration, and scores of all KOOS subscales (p < 0.01). Conclusion: Patients with unilateral knee OA and pain showed more asymmetry of lateral COP-shift during walking compared with matched healthy controls. In addition, larger asymmetry of lateral COP-shift has the moderate or strong association with worse of knee pain, worse in KOOS scores and longer duration of knee pain. Asymmetry of lateral COP-shift during walking may be one of the characteristics of unilateral knee OA as the compensatory strategy response to unilateral OA of the knee.

Co (II), Cu (II), Mn (II), Ni (II), Pd (II), and Pt (II) complexes of bidentate Schiff base ligand: Synthesis, crystal structure, and acute toxicity evaluation

5‐methoxy‐2‐(((2chloro‐5‐(trifluoromethyl)phenyl)imino)methyl)phenol) (HL) and its cobalt (II), copper (II), manganese (II), nickel (II), palladium (II), and platinum (II) complexes, [Co(L)2]·4H2O (1), [Cu(L)2] (2), [Mn(L)2(H2O)2]·H2O (3), [Ni(L)2] (4), [Pd(L)2] (5), [Pt(L)2] (6), were synthesized and characterized. The compounds were investigated by different physico‐chemical techniques including IR, 1H‐NMR, 13C‐NMR, UV‐Vis, mass spectroscopies, elemental and thermal analysis, magnetic susceptibility measurements, and molar electric conductivity. The molecular structures of the HL ligand and copper (II), nickel (II), and palladium (II) complexes were confirmed by X‐ray crystallography analysis on the monocrystal. Each metal ion, in these complexes, is four‐coordinated in N2O2 coordination environment. The coordination geometry of Ni2+ and Pd2+ is square planar due to cystallographically imposed inversion symmetry of the metal centers, and the coordination geometry of copper atom can be described as tetrahedrally distorted square planar. The assessed toxicity of the ligand and its complex combinations on plant cell of Triticum aestivum L. were macroscopically and microscopically consistent. The same substances were investigated for the animal cell toxicity on crustacean Artemia franciscana Kellogg, and Mn2+ complex did not record any lethal effect.

Enhanced green up-conversion luminescence in In2O3:Yb3+/Er3+ by tri-doping Zn2+

By co-doping Yb3+/Er3+ into ordinary material In2O3, the up-conversion glow behavior will be triggered up. On this basis, the luminescence intensity can be significantly improved by tri-doping Zn2+ ions. Compared with In2O3:Yb3+/Er3+, the luminescence intensity of In2O3:Yb3+/Er3+/Zn2+ is significantly enhanced and the emitting light changes from faint red to bright green. This can be attributed to the reduction of site symmetry of the luminescence center and the promotion of crystallinity because of lattice distortion caused by Zn2+ ions. The up-conversion luminescence of the In2O3:Yb3+/Er3+/Zn2+ in the red and green light regions are two-photon excitation process, and the quantum yield (QY) is calculated to be 0.1%. The luminescence at the 524 nm emission peak corresponds to the transition Er3+:2H11/2 → 4I15/2. Other two emission peaks in green area (550 nm, 564 nm) correspond to the transition Er3+:4S3/2 → 4I15/2. And the emission peaks in red area (659 nm, 683 nm) root in the transition Er3+:4F9/2 → 4I15/2.

Altering the nature of coupling by changing the oxidation state in a {Mn6} cage.

Polynuclear transition metal complexes have continuously attracted interest owing to their peculiar electronic and magnetic properties which are influenced by the symmetry and connectivity of the metal centres. Understanding the full electronic picture in such cases often becomes difficult owing to the presence of multiple bridges between metal centres. We have investigated the electronic structure of a {Mn6} cage complex using computational and experimental approaches with the aim to understand the coupling between the manganese centres. The nature of the various coupling pathways has been determined using a novel methodology that involves perturbing the system while retaining the symmetry and analysing the effect on the coupling strength due to the perturbation. Furthermore, we have investigated the magnetic properties of this complex in higher oxidation states which reveals a switch in the nature of coupling from antiferromagnetic to ferromagnetic in addition to stabilisation of intermediate spin states.

A DFT-based theoretical model for the calculation of spectral profiles of lanthanide M4,5-edge x-ray absorption.

This presentation reports the theoretical study of 3d core-electron excitation in lanthanide compounds in terms of electronic structure effects and optical properties. The calculations are done at the Density-Functional Theory (DFT) level complemented with an effective Hamiltonian based on ligand-field theory. The strategy consists of obtaining from DFT a totally symmetric density, where an active subspace is set up that forms the basis of the fivefold 3d and sevenfold 4f atomic orbitals of the lanthanide ion. This active subspace is defined with the fractional occupation of electrons, which represents open-shell species with the composite configuration 3d94fn+1. Based on the ligand-field analysis of the DFT results, the multiplet energies and ligand-field effects associated with the configuration 3d94fn+1 are evaluated; and the X-ray absorption spectra are simulated in terms of the intra-atomic 4fn → 3d94fn+1 electron transitions within the electric-dipole approximation. Examples for application are proposed taking into consideration the isolated trivalent lanthanides ions and compounds Cs2NaPrX6, with X = F, Cl, and Br. The results are compared with available experimental data, where a good agreement is qualitatively achieved. Also, the screening of the inter-electron repulsion and spin-orbit coupling interaction is numerically obtained that allows one to establish a fully non-empirical treatment of the 3d core-electron excitation, which can be valuable in the characterization and modeling of the spectral profiles of lanthanide M4,5-edge X-ray absorption spectroscopy. The enclosed theoretical model, which is being implemented in the Amsterdam Density Functional (ADF) suite of programs, is computationally economic and can be applied to any lanthanide system without limitations in terms of the size of the matrix elements of the effective Hamiltonian or the coordination symmetry of the lanthanide center.

Solid state photoluminescence studies of [EuLnH2(NO3)3](H2O)x macrocyclic complexes with Schiff base ligands

Three EuIII macrocyclic complexes [EuLnH2(NO3)3](H2O)x based on the ligands derived from 2-hydroxy-5-methyl-1,3-benzenedicarbaldehyde and three different amines: o-phenylenediamine, Eu-OPDA; ethylenediamine, Eu-EDA; and 1,3-diaminopropane, Eu-DAP have been synthesized via a metal template reaction. Eu-EDA and Eu-DAP showed metal based emission; for the Eu-OPDA complex these luminescent properties were not observed. From the photoluminescence emission measurements from ~13 to 300 K, the R/O = I (5D0 → 7F2)/I (5D0 → 7F1) ratio, together with two intensity parameters (Ω2 and Ω4), radiative lifetimes (τR) and branching ratios (β0 J′) were calculated based on the Judd-Ofelt theory, for Eu-EDA and Eu-DAP. While the behavior of these parameters for the Eu-DAP complex is temperature dependent, these remain constant for Eu-EDA. The temperature dependence observed for the Eu-DAP complex indicates that for temperatures below 120 K, the local symmetry of the EuIII center is modified, as compared to the environment of the same metal center at room temperature.

Testing for central symmetry and inference of the unknown center

In this paper, we consider testing for central symmetry and inference of the unknown center with multivariate data. Our proposed test statistics are based on weighted integrals of empirical characteristic functions. With two special weight functions, we obtain test statistics with simple and closed forms. The test statistics are easy to implement. In fact, they are based merely on pairwise distances between points in the sample. The asymptotic results are developed. It is proven that our proposed tests can converge to finite limit at the rate of n−1 under the null hypothesis and can detect any fixed alternatives. For the unknown center, we also propose two classes of minimum distance estimators based on the previously introduced test statistics. The asymptotic normalities are derived. Efficient algorithms are also developed to compute the estimators in practice. We further consider checking whether the unknown center is equal to a specified value μ0. Extensive simulation studies and one medical data analysis are conducted to illustrate the merits of the proposed methods.

Identification of environment symmetry for iron centers in aluminosilicates by EPR

We study an angular dependence of EPR spectra of the own defects in topaz (Al2[SiO4][F,OH]2). The topaz crystal structure is built of silicon-oxygen tetrahedral (SiO4) and octahedral aluminum surrounded by four oxygen ions and fluorine ions or a hydroxyl group. There are two types of substitution defects in topaz, such as octahedral and tetrahedral, depending on the location of the impurity ion. The point defects with octahedral symmetry arise on local substitution of aluminum (Fe3+ → Al3+), while tetrahedral coordinated centers are formed by substitution of silicon (Fe3+→ Si4+) in the silicon-oxygen tetrahedral (SiO4). To determine the symmetry of the impurity centers, the angular dependence of the EPR spectrum is calculated. The excited energy states for defects are determined by the magnitude of the g-factor shift. These states equal 1.6 eV and 3.2 eV, respectively. A super-hyperthin structure (SHTS) of the EPR lines of iron has been observed. This SHTS is determined by the magnetic moments of the fluorine nuclei F19 located in the first coordination sphere of the paramagnetic iron center. The models of the three new paramagnetic centers in topazes are suggested, one of them being of orthorhombic symmetry for aluminum substitution and the two others being of tetragonal symmetry for silicon substitution with oxygen vacancies.

Coupled electron-ion Monte Carlo simulation of hydrogen molecular crystals.

We performed simulations for solid molecular hydrogen at high pressures (250 GPa ≤ P ≤ 500 GPa) along two isotherms at T = 200 K (phase III) and at T = 414 K (phase IV). At T = 200 K, we considered likely candidates for phase III, the C2c and Cmca12 structures, while at T = 414 K in phase IV, we studied the Pc48 structure. We employed both Coupled Electron-Ion Monte Carlo (CEIMC) and Path Integral Molecular Dynamics (PIMD). The latter is based on Density Functional Theory (DFT) with the van der Waals approximation (vdW-DF). The comparison between the two methods allows us to address the question of the accuracy of the exchange-correlation approximation of DFT for thermal and quantum protons without recurring to perturbation theories. In general, we find that atomic and molecular fluctuations in PIMD are larger than in CEIMC which suggests that the potential energy surface from vdW-DF is less structured than the one from quantum Monte Carlo. We find qualitatively different behaviors for systems prepared in the C2c structure for increasing pressure. Within PIMD, the C2c structure is dynamically partially stable for P ≤ 250 GPa only: it retains the symmetry of the molecular centers but not the molecular orientation; at intermediate pressures, it develops layered structures like Pbcn or Ibam and transforms to the metallic Cmca-4 structure at P ≥ 450 GPa. Instead, within CEIMC, the C2c structure is found to be dynamically stable at least up to 450 GPa; at increasing pressure, the molecular bond length increases and the nuclear correlation decreases. For the other two structures, the two methods are in qualitative agreement although quantitative differences remain. We discuss various structural properties and the electrical conductivity. We find that these structures become conducting around 350 GPa but the metallic Drude-like behavior is reached only at around 500 GPa, consistent with recent experimental claims.

Symmetry and diffusivity of the interstitial hydrogen shallow-donor center in In2O3

Uniaxial-stress experiments performed for the 3306 cm−1 vibrational line assigned to the interstitial-hydrogen, shallow-donor center in In2O3 reveal its symmetry and transition-moment direction. The defect alignment that can be produced by a [001] stress applied at 165 K is due to a process that is also a hydrogen-diffusion jump, providing a microscopic determination of the diffusion constant for H in In2O3 and its mechanism. Our experimental results strongly complement the theoretical predictions for the structure and diffusion of the interstitial hydrogen donor center in In2O3.