Iodine Atoms Research Articles

Synthesis and Spectral Properties of Iodine-Substituted Dyes Based on Benzothiazolium Salts

Two series of new thiacarbocyanines with iodine atoms in the donor and/or acceptor block have been synthesized. The absorption spectra of the iodinated dyes in the region of singlet-singlet S0-S1 and singlet-triplet S0-T1 transitions are investigated. The introduction of iodine atoms into the dye structures leads to a red shift of the absorption maximum, regardless of the position of iodine in the molecule. For dyes with two or more iodine atoms, a low-intensity long-wave absorption shoulder in the region from 650 to 1000 nm is detected, which corresponds to singlet-triplet absorption.

Correlation between CT spectral quantitative parameters and expression levels of HIF-1α and ALX1 in non-small cell lung cancer.

To detect the expression levels of hypoxia inducible factor-1alpha (HIF-1α) and aristaless-like homeobox 1 (ALX1) in non-small cell lung cancer and analyze the relationship between CT spectral quantitative parameters and immunohistochemical markers, in order to evaluate the biological characteristics of lung cancer by spectral CT. Spectral CT data and paraffin masses of 50 adult patients with lung cancer were collected. CT quantitative parameters including the slope of spectral curve, effective atomic number and iodine concentration in enhanced phases were acquired. Expression levels of HIF-1α and ALX1 were detected by immunohistochemical tests, and compared between different pathological types and differentiation grades of tumor cells. CT quantitative parameters at different expression levels of HIF-1α and ALX1 were compared, respectively. The relationship between CT quantitative parameters and expression levels of HIF-1α and ALX1 were analyzed. There was no significant difference of expression levels of HIF-1α and ALX1 between adenocarcinoma and squamous cell carcinoma. Expression levels of HIF-1α among different differentiation grades of tumor cells had significant difference (χ2 = 27.100, P < .001), while without significant difference in ALX1 expression. CT spectral parameters had significant difference among expression levels of HIF-1α and ALX1 (P < .01). There was a positive correlation between each CT spectral parameter and the expression level of immunohistochemical markers. CT spectral quantitative parameters are significantly different among expression levels of immunohistochemical markers. The positive correlation between CT quantitative parameter and expression level of immunohistochemical markers suggests CT spectral imaging could predict biological characteristics of tumors.

Molecular Oxygen (O2) Artifacts in Tandem Mass Spectra.

Peak annotation plays an important role in mass spectral evaluation of the NIST 2023 tandem mass spectral library. While most fragment ions are formed by neutral losses, there are peaks that represent adduct ions from these fragments. Previously, we have reported two main types of addition reactions in the collision cell, namely addition of H2O and N2. Here we report a different reaction in the collision cell, with addition of O2 leading to a small peak that could only be assigned to a peroxyl radical ion. For example, some protonated iodoaromatics lose an iodine atom to form a radical cation [M+H-I]+•, which reacts with O2 to generate a peroxyl radical ion [M+H-I+O2]+•. Higher concentrations of O2 result in higher peroxyl radical peaks, which become dominant while the precursor ions are consumed, as examined by five compounds under different concentrations of O2. The correlation of the peroxyl radical peak intensities to the concentration of O2 provides a tool to estimate trace amounts of O2 within the instrument. In the NIST 2023 tandem mass spectral library, the peaks for [M+H-X+O2]+· are most abundant in numbers and in intensity for X = NO2 or I, are much less abundant for X = Br, and are rare for X = Cl. Other leaving groups in this library are SO3H, SO2NH2, CSNH2, CO2C6F5, SO2CH3, and COCH3. The O2 addition reaction is also observed with negative ions in this library. While adducts of H2O and N2 often constitute major peaks, the peaks of the peroxyl radicals under standard conditions are mostly very small and may be mistaken for noise, but their correct annotation improves the quality of the spectra and is important when comparing spectra from different instruments or conditions.

Unravelling the intricacies of fluorescence enhancement in heptamethine cyanine dyes induced by heavy halogen atoms

The classic heavy-atom effect refers to the photophysical phenomenon observed in fluorophores, where the interaction with heavy atoms quenches fluorescence emission. Many fluorophores containing heavy halogen atoms, such as xanthenes, BODIPYs, porphyrins, and anthracenes, adhere to this effect, while the photophysical behavior of others, e.g. halogenated heptamethine cyanine dyes, is poorly studied having contradicting results. In this study, we explored for the first time unexpected fluorescence enhancement induced by heavy halogen atoms in heptamethine dyes, contrasting the classic heavy-atom effect. To this end, a series of novel heptamethine cyanine dyes were synthesized and their photophysical properties were experimentally and theoretically investigated. Heavy halogen atoms were found to significantly affect the fluorescence behaviour of heptamethine dyes depending on the number and position of the attached halogens. Thus, the introduction of bromine and iodine atoms at the non-conjugated positions to the chromophore moieties led to an increase in the fluorescence quantum yields, which contradicts the classic principle and could be explained by heavy halogen-induced vibration restrictions. The value of halogen atom-promoted singlet oxygen generation quantum yield ΦΔ is also not straightforward and depends on the number, position and weight of the halogen atom. The breaking of the classic heavy-atom effect in halogenated heptamethine dyes provides an effective strategy to substantially increase the fluorescence intensity of long-wavelength cyanine dyes, providing new functional advantages for fluorescence imaging, diagnostics, and photodynamic therapy, among other applications.

Low current iodine-fed hollow cathode discharge: insights from fluid model

Abstract As one of the fundamental components, hollow cathodes using noble gas propellant are widely used in electric thrusters. Iodine has become one of the ideal alternative propellants due to its economy and good chemical properties, while due to the complex reactions, characteristics and proper functioning of iodine-fed hollow cathodes are still unknown. Therefore, a model is needed to understand the physical-chemical process of the iodine-fed hollow cathode discharge. In this work, a self-consistent two-dimensional fluid model of the low-current iodine-fed hollow cathode discharge with detailed non-equilibrium plasma chemistry is developed and verified by the voltages of the keeper and anode obtained in the experiments. Simulations show that the electron impact ionization with iodine atoms dominates the discharge process as the density of iodine atoms is much higher than that of iodine molecules due to the electron impact dissociation and thermal dissociation. Moreover, the power balance analysis shows the heating of electrons contributed by the electric field mainly takes place near the keeper and the orifice. Ion current heating contributes significantly to the gas heating compared with the heating by the electron elastic collisions with I and I2 and the heat release or consumption during the neutral reactions. Furthermore, the influence of electronegativity on plasma characteristics is analysed. Simulations involving I− ions bring higher values of ionization degree, discharge power as well as maximum electron and gas temperatures compared with those without I−. This is similar to the differences in the plasma properties between the iodine-fed and xenon-fed hollow cathode to which the low ionization energy, large collision ionization cross-section and the electronegativity of iodine contribute together. In all, these findings can better predict the plasma behaviours in the iodine-fed hollow cathode discharge and may promote the development of the electric propulsion system using iodine propellant.

Molecular Evidence for the Axial Coordination Effect of Atomic Iodine on Fe‐N4 Sites in Oxygen Reduction Reaction

AbstractWe present a molecular‐scale investigation of the axial coordination effect of atomic iodine on Fe‐N4 sites in the oxygen reduction reaction (ORR) by electrochemical scanning tunneling microscopy (ECSTM). A well‐defined model catalytic system with explicit and uniform iodine‐coordinated Fe‐N4 sites was constructed facilely by the self‐assembly of iron(II) phthalocyanine (FePc) on an I‐modified Au(111) surface. The electrocatalytic activity of FePc for the ORR shows notable enhancement with axial iodine ligands. The modulation of the electronic structure of Fe sites to evoke a higher spin configuration by axial iodine was evidenced. The interaction strength between oxygen‐containing species and active centers becomes weaker due to the presence of iodine ligands, and the reaction is thermodynamically preferable. Furthermore, the reaction dynamics of FePc on I/Au(111) were explicitly determined via in situ ECSTM potential pulse experiments. In contrast, axial atomic iodine was found inefficacious for improving the activity of Co‐N4 sites, and electron rearrangement was found to be marginal, demonstrating that adequate interactions between axial ligands and metal sites for optimizing electronic structures and catalytic behaviors are prerequisites for the impactful role of axial ligands.

Synthesis and Anticancer Properties of Heterobimetallic Fe(II)/Pd(II) Complexes Bearing Different Butadienyl Fragments

AbstractIn this work, we describe the synthesis of heterobimetallic Fe(II)/Pd(II) complexes bearing different halides and halide‐substituted butadienyl ligands. The synthetic approach involves the preparation of suitable Pd(II)‐butadienyl precursors containing a thioquinoline moiety, followed by the substitution of this relatively labile ligand with dppf (dppf=1,1′‐bis(diphenylphosphino)ferrocene). With the exception of complexes containing at least one iodine atom, all compounds were synthesized in high yields and purity, and thoroughly characterized using spectroscopic and diffractometric methods. The investigation of the antiproliferative activity of the synthesized organometallic complexes against ovarian and breast cancer cell lines revealed that all compounds exhibit noteworthy cytotoxicity, with IC50 values in the micromolar range and generally comparable to those of cisplatin. Interestingly, significant differences of cytotoxicity among the analysed compounds were observed in the case of MRC‐5 normal cells. Of particular interest is the dichloride derivative 3 a, which is essentially inactive towards non‐cancerous cells (IC50&gt;100 μM), thus demonstrating promising in vitro selectivity that we believe warrants further investigation in the future.

Investigation of the reaction of hydrogen iodide with a chlorine atom in the atmosphere above the sea

By the method of resonant fluorescence (RF) of chlorine atoms and iodine atoms, the rate constant of the reaction of a chlorine atom with hydrogen iodide at a temperature of 298 K. The values of the reaction constants measured by both methods turned out to be quite close. The role of this reaction in the chemistry of the troposphere above the surface of the oceans is discussed.

Structural, electronic, optical and thermoelectric properties of FrSnI3-xFx (X=0, 1, 2, 3) perovskites using the TB-mBJ approach

In this study, we investigate the structural, optical, electronic, and thermoelectric properties of FrSnI3-xFₓ (x = 0, 1, 2, 3) perovskites using density functional theory with the modified Becke-Johnson method (TB-mBJ) for exchange correlation functions. This research is the first theoretical investigation of these promising materials. Our results show that each variant of the perovskite exhibits p-type semiconductor behavior, and that the energy gap of FrSnI₃ can be tuned by substituting an iodine atom with fluorine. This substitution causes a significant variation in the energy gap, ranging from 1.169 eV to 2.951 eV. In particular, the FrSnI₂F compound stands out with a direct gap of 1.539 eV, making it an ideal candidate for solar cell applications. Optical properties, including real and imaginary dielectric function components, absorption and refractive indices, highlight the performance of these materials. Their high absorption capabilities suggest that these perovskites can be tailored and integrated into optical and optoelectronic devices in a variety of spectral ranges.Furthermore, thermoelectric property calculations using BoltzTrap software show that FrSnI3-xFₓ (x = 0, 1, 2, 3) has a promising Seebeck coefficient and an impressive figure of merit approaching unity at high temperatures. These results underscore the immense potential of these materials in thermoelectric applications, opening the door to new possibilities in energy conversion technology.

Acyclic Diaminocarbene Platinum(IV) Complexes Synthesized by the Oxidative Addition of MeI and I&lt;sub&gt;2&lt;/sub&gt;

The oxidative addition of methyl iodide or molecular iodine to the bis(С,N-chelate) deprotonated diaminocarbene platinum(II) complexes [Pt{C(N(H)Ar)(NC(N(H)Ph)N(Ph)}2] (Ar = C6H3-2,6-Me2 (Xyl), C6H2-2,4,6-Me3 (Mes), and C6H4-4-Me (pTol)) affords the corresponding platinum(IV) derivatives in a yield of 89–99%. The addition of CF3CO2H is accompanied by the protonation of the nitrogen atoms of the diaminocarbene fragment to form the cationic complexes [[PtI(X)-{C(N(H)Ar)(NC(N(H)Ph)N(Ph)}2]CF3CO2H (X = Me, I). The structures of the compounds are determined by elemental analysis; high resolution mass spectrometry with electrospray ionization (ESI HRMS); IR spectroscopy; 1H, 13C{1H}, 19F{1H}, and 195Pt{1H} NMR spectroscopy; 2D NMR spectroscopy (1H,1Н COSY, 1H,1Н NOESY, 1H,13C HSQC, 1H,13C HMBC, 1H,15N HSQC, 1H,15N HMBC), and X-ray diffraction (XRD) and thermogravimetric analyses. The synthesized platinum(IV) complexes are thermally stable to 200–260°C and are electroneutral molecules with the octahedral coordination sphere formed by two deprotonated diaminocarbene C,N-chelate substituents and iodine and methyl or two iodine atoms localized in the apical positions.

Unveiling elevated curie temperature and exceptional perpendicular magnetic anisotropy in chlorinated monolayer CrI3

Due to the finite band gap and a ferromagnetic ground state, the CrI3 monolayer is attracting great research interests. However, the low Curie temperature of 46 K is one of the major obstacles for spintronics applications. Here, we have investigated the magnetic properties of chlorinated CrI3 monolayer with varying concentration of Cl. We investigated the dynamical and thermal stability by phonon dispersion and ab-initio molecular dynamic simulation. The band gap was decreasing with increasing Cl concentration and a half-metallic state is obtained at Cl concentration of 4.22 × 1014/cm2. The pristine CrI3 monolayer had perpendicular magnetic anisotropy energy of 0.84 meV/Cr. We find that this perpendicular magnetic anisotropy energy can be even enhanced twice by chlorination. Due to the hybridization of I and Cr atom, we found the spin asymmetric density of states in the iodine atom and this strong enhancement in the magnetic anisotropy originated from asymmetric spin features in iodine atom. We propose that the chlorination can increase the Curie temperature up to 204 K and this is almost four times enhanced value. Based on these finding, we propose that the chlorinated CrI3 system can be a promising material for spintronics applications.

Surface Chemistry Regulation in Cu4I4-Triazolate Metal-Organic Frameworks for One-Step C3H6 Purification from Quaternary C3 Mixtures.

C3H6 is a crucial building block for many chemicals, yet separating it from other C3 hydrocarbons presents a significant challenge. Herein, we report a hydrolytically stable Cu4I4-triazolate metal-organic framework (MOF) (JNU-9-CH3) featuring 1D channels decorated with readily accessible iodine and nitrogen atoms from Cu4I4 clusters and triazolate linkers, respectively. The exposed iodine and nitrogen atoms allow for cooperative binding of C3 hydrocarbons, as evidenced by in situ single-crystal crystallography and Raman spectroscopy studies. As a result, JNU-9-CH3 exhibits substantially stronger binding affinity for C3H4, CH2═C═CH2, and C3H8 than that for C3H6. Breakthrough experiments confirm its ability to directly separate C3H6 (≥99.99%) from C3H4/CH2═C═CH2/C3H8/C3H6 mixtures at varying ratios and flow rates. Overall, we illustrate the cooperative binding of C3 hydrocarbons in a Cu4I4-triazolate MOF and its highly efficient C3H6 purification from quaternary C3 mixtures. The study highlights the potential of MOF adsorbents with metal-iodide clusters for cooperative bindings and hydrocarbon separations.

Biodegradable copper-iodide clusters modulate mitochondrial function and suppress tumor growth under ultralow-dose X-ray irradiation

Both copper (Cu2+/+) and iodine (I−) are essential elements in all living organisms. Increasing the intracellular concentrations of Cu or I ions may efficiently inhibit tumor growth. However, efficient delivery of Cu and I ions into tumor cells is still a challenge, as Cu chelation and iodide salts are highly water-soluble and can release in untargeted tissue. Here we report mitochondria-targeted Cu-I cluster nanoparticles using the reaction of Cu+ and I− to form stable bovine serum albumin (BSA) radiation-induced phosphors (Cu-I@BSA). These solve the stability issues of Cu+ and I− ions. Cu-I@BSA exhibit bright radioluminescence, and easily conjugate with the emission-matched photosensitizer and targeting molecule using functional groups on the surface of BSA. Investigations in vitro and in vivo demonstrate that radioluminescence under low-dose X-ray irradiation excites the conjugated photosensitizer to generate singlet oxygen, and combines with the radiosensitization mechanism of the heavy atom of iodine, resulting in efficient tumor inhibition in female mice. Furthermore, our study reveals that BSA protection causes the biodegradable Cu-I clusters to release free Cu and I ions and induce cell death by modulating mitochondrial function, damaging DNA, disrupting the tricarboxylic acid cycle, decreasing ATP generation, amplifying oxidative stress, and boosting the Bcl-2 pathway.

The Impact of Bromine Surface Doping on the Structural, Optical, and Morphological Properties of Bismuth‐Based Perovskite Film as a Light‐Absorber in Perovskite Solar Cells

Bismuth‐based perovskite materials have concerned significant attention due to their low‐toxic and stable properties. However, achieving smooth and dense thin films for the preferential growth of bismuth‐based perovskite along the c‐axis, which is conducive to the preparation of solar cells, is challenging. Therefore, using halogen atoms to partially replace iodine atoms and constrain anisotropic growth has been shown to be an effective method for obtaining high‐quality perovskite films. Herein, Br doping with varying concentrations is used to treat bismuth‐based perovskite films with larger and denser grains compared to those without doping. When a small amount of Br ions is doped, the surface of the perovskite layer becomes more uniform, significantly improving the compactness of the perovskite film. Additionally, proper Br doping can reduce internal defects in the films, effectively inhibiting nonradiative recombination, enhancing light absorption, and increasing carrier lifetime. The optimal power conversion efficiency of Br‐doped bismuth halide perovskite solar cells is found to be 0.136%, compared to 0.087% for pristine devices.

Crystal chemical investigations on TiU8S17 and U36Lu21S93I3 - ordered and disordered multinary uranium sulfides

The crystal chemistry of uranium sulfides is characterized by a large diversity in composition, crystal structures, oxidation states and physical properties. This holds also for TiU8S17 and U36Lu21S93I3, of which large single crystals up to several mm in length were grown by chemical vapor transport using iodine as a transport agent. TiU8S17 crystallizes with the monoclinic CrU8S17 structure type (C2/m, a = 13.3477(2) Å, b = 8.4927(2) Å, c = 10.4836(2) Å, β = 101.207(2)°) featuring distorted octahedra [TiS6] and bicapped trigonal prisms [US8]. Interatomic distances and X-ray photoelectron spectra indicate tetravalent uranium. Disordered U36Lu21S93I3 represents a new structure type (R3¯m, 13.3841(2) Å, 20.6447(2) Å) with an average crystal structure exhibiting square antiprisms [LuS8], bi- and tricapped trigonal prisms [US8] and [US9] and distorted octahedra [IU6]. Lutetium and sulfur atoms are disordered similar to Ce53Fe12S90X3, La53Fe12S90X3 (X = Cl, Br, I) and La52Fe12S90. This might be caused by positional shifts of iodine atoms away from the center of the polyhedron, thus avoiding unusually long U–I distances and severely disrupting the order of neighboring lutetium and sulfur atoms. The results of chemical analyses (ICP-MS, EDX), electron microscopy (TEM) and X-ray photoelectron spectroscopy support the composition and crystal structure of U36Lu21S93I3 and indicate mixed valency of uranium and charge balance according to the crystal chemical formula (U+III)18(U+IV)18(Lu+III)21(S-II)93(I–I)3.

Near-infrared hemicyanine photosensitizer for targeted mitochondrial viscosity imaging and efficient photodynamic therapy

As a severe threat to human health, cancer has always been one of the most significant challenges facing the medical field. However, there is currently no effective technology or method to diagnose and treat cancer simultaneously. Therefore, developing a new approach that integrates diagnosis and treatment holds promise as a means of achieving personalized and precise cancer therapy. In this study, we developed a novel dual-functional near-infrared mitochondrial-targeted photosensitizer, Hcy-I, which is capable of simultaneously monitoring cellular viscosity and specifically targeting mitochondria for photodynamic therapy. Compared with traditional hemicyanine dyes, the introduction of iodine atoms in Hcy-I enhanced spin–orbit coupling (SOC) and promoted the intersystem crossing (ISC) rate, thereby increasing the efficiency of singlet oxygen (1O2) generation. In vitro experiments demonstrated that Hcy-I exhibited high sensitivity to viscosity variations and efficiently generated 1O2 under 638 nm laser irradiation, with an 1O2 quantum yield of up to 48.9 %. Cell experiments further revealed that this photosensitizer could effectively target mitochondria for photodynamic therapy, disrupting mitochondrial membrane potential and inducing cell death. When treated with Hcy-I at a concentration of 0.8 µM, the survival rate of HepG-2 cells was only 13 %. These results suggested that Hcy-I had the potential to integrate cancer diagnosis and treatment. The research not only promotes the development of photodynamic thereby technology, but also opens up new avenues for the diagnosis and treatment of cancer.

Accelerating the discovery of type Ⅱ photosensitizer: Experimentally validated machine learning models for predicting the singlet oxygen quantum yield of photosensitive molecule

Photodynamic therapy (PDT) is an emerging cancer treatment that mainly relies on photosensitizer (PS) to generate singlet oxygen for tumor destruction. Developing PSs with high singlet oxygen quantum yields (SO-QYs) requires extensive experimentation, limiting their rapid screening. Herein, to streamline this process, this study introduces several machine learning (ML) models that accurately predicts SO-QY across various experimental conditions. The models’ establishment is based on two feature matrices derived from Morgan fingerprints (MFPs) and descriptors (molecular descriptors and quantum chemical descriptors, MD_QCDs). Comparative and evaluative results indicate that the XGBoost model constructed with MFPs and the AdaBoost model constructed with MD_QCDs exhibit superior predictive performance, with R2 values of 0.8648 and 0.8460, respectively. Furthermore, by utilizing SHapley Additive exPlanations (SHAP) analysis and quantum chemistry, we analyzed that the iodine atoms and larger conjugated systems significantly influenced the SO-QY. Experimental validation, based on this analysis, demonstrates that our models not only possess excellent predictive capabilities but also exhibit strong interpretability. In summary, this work has established several interpretable models with outstanding predictive performance, which can aid in the more rapid screening of PSs, thus promoting their application in PDT.

Pyrazolyliodonium platinum(II) trichloride features the highest positive electrostatic potential on the iodine atom among uncharged halogen bond donors

This study presents a new uncharged platinum(II) complex with a pyrazolyliodonium ligand, which features an exceptionally large σ-hole on the iodine atom. Single-crystal X-ray diffraction analysis reveals the structure of the [LPtCl3]·2DMF complex, highlighting two types of intermolecular halogen bonds: a C−I⋯O bond with DMF and C−I⋯Cl bonds with the platinum complex. Quantum chemical calculations confirm the high positive electrostatic potential on the iodine σ-hole, demonstrating its significant halogen bond donor ability.

Supramolecular Assembly of Cesium Copper Iodine Resulting in Rich Emission Properties

AbstractCrown ether‐assisted supramolecular assembly is a robust strategy for manipulating low‐dimensional metal halides. In this study, the supramolecular assembly of 0D‐Cs3Cu2I5 is presented. Upon the addition of 15‐crown‐5 (15C5) to Cs3Cu2I5, 15C5 immediately coordinates with Cs+ to form the cone‐shaped [(15C5)Cs]+. Simultaneously, one of the iodine atoms is removed from the [Cu2I5]3‐ cluster, resulting in the formation of a sub‐planar rhombic [Cu2I4]2− unit. This process leads to white emission, specifically [(15C5)Cs]2[Cu2I4], which exhibits a photoluminescence quantum yield (PLQY) close to unity. The [(15C5)Cs]+ further reacts with 15C5 to form the sandwich‐type cationic structure [(15C5)2Cs]+, accompanied by the generation of red emission [(15C5)2Cs]2[Cu2I4]. By carefully controlling the amount of 15C5, various emission composites can be achieved, particularly tunable white emission. The assembly process is reversible. The pristine Cs3Cu2I5 can be recovered after thermal curing because of the volatility of crown ether and the weak Cs‐crown ether bond. Theoretical calculations have demonstrated that the coordination of the crown ether primarily affects the energy level, leading to changes in the excited state and photophysical properties. The applications in anticounterfeiting and LED phosphors have been demonstrated. This work provides a new approach for the development of low‐dimensional copper halides with promising applications in optoelectronics.

Hydrogen Bonding Analysis of Structural Transition-Induced Symmetry Breaking and Spin Splitting in a Hybrid Perovskite Employing a Synergistic Diffraction-DFT Approach.

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) offer an outstanding opportunity for spin-related technologies owing in part to their tunable structural symmetry breaking and distortions driven by organic-inorganic hydrogen (H) bonds. However, understanding how H-bonds tailor inorganic symmetry and distortions and therefore enhance spin splitting for more effective spin manipulation remains imprecise due to challenges in measuring H atom positions using X-ray diffraction. Here, we report a thermally induced structural transition (at ∼209 K) for a 2D HOIP, (2-BrPEA)2PbI4 [2-BrPEA = 2-(2-bromophenyl)ethylammonium], which induces inversion asymmetry and a strong spin splitting (ΔE > 30 meV). While X-ray diffraction generally establishes heavy atom coordinates, we utilize neutron diffraction for accurate H atom position determination, demonstrating that the structural transition-induced rearrangement of H-bonds with distinct bond strengths asymmetrically shifts associated iodine atom positions. Consequences of this shift include an increased structural asymmetry, an enhanced difference between adjacent interoctahedra distortions (i.e., Pb-I-Pb bond angles), and therefore significant spin splitting. We further show that H-only density-functional theory (DFT) relaxation of the X-ray structure shifts H atoms to positions that are consistent with the neutron experimental data, validating a convenient pathway to more generally improve upon HOIP H-bonding analyses derived from quicker/less-expensive X-ray data.