Observation of Ferromagnetism in Dilute Magnetic Halide Perovskite Semiconductors.

Dilute magnetic semiconductors (DMSs) have attracted much attention because of their potential use in spintronic devices. Here, we demonstrate the observation of robust ferromagnetism in a solution-processable halide perovskite semiconductor with dilute magnetic ions. By codoping of magnetic (Fe2+) and aliovalent (Bi3+) metal ions into CH3NH3PbCl3 (MAPbCl3) perovskite, ferromagnetism with well-saturated magnetic hysteresis loops and a maximum coercivity field of 1280 Oe was observed below 12 K. The ferromagnetic resonance measurements revealed that the incorporation of aliovalent ions modulates the carrier concentration and plays an essential role in realizing the ferromagnetism in dilute magnetic halide perovskites. Magnetic ions are proposed to interact through itinerant charge carriers to achieve ferromagnetic coupling. Our work provides a new avenue for the development of solution-processable magnetic semiconductors.

Efficient Green Spin Light-Emitting Diodes Enabled by Ultrafast Energy- and Spin-Funneling in Chiral Perovskites.

Introducing molecular chirality into perovskite crystal structures has enabled the control of carrier spin states, giving rise to circularly polarized luminescence (CPL) in thin films and circularly polarized electroluminescence (CPEL) in LEDs. Spin-LEDs can be fabricated either through a spin-filtering layer enabled by chiral-induced spin selectivity or a chiral emissive layer. The former requires a high degree of spin polarization and a compatible spinterface for efficient spin injection, which might not be easily integrated into LEDs. Alternatively, a chiral emissive layer can also generate circularly polarized electroluminescence, but the efficiency remains low and the fundamental mechanism is elusive. In this work, we report an efficient green LED based on quasi-two-dimensional (quasi-2D) chiral perovskites as the emitting layer (EML), where CPEL is directly produced without separate carrier spin injection. The optimized chiral perovskite thin films exhibited strong CPL at 535 nm with a photoluminescence quantum yield (PLQY) of 91% and a photoluminescence dissymmetry factor (glum) of 8.6 × 10-2. Efficient green spin-LEDs were successfully demonstrated, with a large EL dissymmetry factor (gEL) of 7.8 × 10-2 and a maximum external quantum efficiency (EQE) of 13.5% at room temperature. Ultrafast transient absorption (TA) spectroscopic study shows that the CPEL is generated from a rapid energy transfer accompanied by spin transfer from 2D to 3D perovskites. Our study not only demonstrates a reliable approach to achieve high performance spin-LEDs but also reveals the fundamental mechanism of CPEL with an emissive layer of chiral perovskites.

Self-Powered and Broadband Photodetectors Based on High-performance Mixed Dimensional Sb2O3/PdTe2/Si Heterojunction for Multiplex Environmental Monitoring.

Solar-blind ultraviolet (SBUV) to near-infrared (NIR) broadband photodetectors (BB-PD) have important applications in environmental monitoring and other applications. However, it is challenging to prepare SBUV-IR photosensitive materials via simple steps and to construct SBUV-IR broadband devices for multiplex detection with high sensitivity at different wavelengths. Here, self-powered and broadband photodetectors using a high-performance mixed dimensional Sb2O3 nanorod 1-dimension (1D)/monodisperse microdiamond-like PdTe2 3-dimension (3D)/Si (3D) heterojunction for multiplex detection of environmental pollutants with high sensitivity at broadband wavelength are developed. The 1D/3D mixed dimensional Sb2O3/PdTe2/Si structure combines the advantages of strong light absorption, high carrier transport efficiency of 1D Sb2O3 nanorods, and expansion of interface barrier caused by 3D microdiamond-like PdTe2 interlayer to improve the photocurrent density and self-powered ability. The efficient photogenerated charge separation enables anon/off ratio of more than 5 × 106. The device exhibits excellent photoelectric properties from 255 to 980 nm with the responsivity from 4.56 × 10-2 to 6.55 × 10-1 AW-1, the detectivity from 2.36 × 1012 to 3.39 × 1013 Jones, and the sensitivity from 3.90 × 107 to 1.10 × 1010 cm2 W-1 without external bias. Finally, the proposed device is applied for the multiplex monitoring of environmental pollution gases NO2 with the detection limit of 200 ppb and PM2.5 particles at mild pollution at broadband wavelength. The proposed BB-PD has great potential for multiplex detection of environmental pollutants and other analytes at broadband wavelength.

Synthesis of Metastable Silver-Lanthanide Double Perovskite Nanocrystals with White-Light Emission.

Four silver-lanthanide double perovskite nanocrystals, namely, Cs2AgSmCl6, Cs2AgEuCl6, Cs2AgGdCl6, and Cs2AgErCl6, were synthesized for the first time. These four double perovskites have yet to be reported in any form and are found to be metastable in the bulk phase. By using the colloidal hot-injection synthesis method, the metastable double perovskite phase can be arrested kinetically. These lead-free nanocrystals show a broadband emission owing to the self-trapped exciton recombination, with Cs2AgEuCl6 exhibiting the characteristic f-f emission from Eu3+.

Risk factor analysis and risk prediction study of obesity in steelworkers: model development based on an occupational health examination cohort dataset.

BACKGROUND: Obesity is increasingly recognized as a grave public health concern globally. It is associated with prevalent diseases including coronary heart disease, fatty liver, type 2 diabetes, and dyslipidemia. Prior research has identified demographic, socioeconomic, lifestyle, and genetic factors as contributors to obesity. Nevertheless, the influence of occupational risk factors on obesity among workers remains under-explored. Investigating risk factors specific to steelworkers is crucial for early detection, prediction, and effective intervention, thereby safeguarding their health. METHODS: This research utilized a cohort study examining health impacts on workers in an iron and steel company in Hebei Province, China. The study involved 5469 participants. By univariate analysis, multifactor analysis, and review of relevant literature, predictor variables were found. Three predictive models-XG Boost, Support Vector Machine (SVM), and Random Forest (RF)-were employed. RESULTS: Univariate analysis and cox proportional hazard regression modeling identified age, gender, smoking and drinking habits, dietary score, physical activity, shift work, exposure to high temperatures, occupational stress, and carbon monoxide exposure as key factors in the development of obesity in steelworkers. Test results indicated accuracies of 0.819, 0.868, and 0.872 for XG Boost, SVM, and RF respectively. Precision rates were 0.571, 0.696, and 0.765, while recall rates were 0.333, 0.592, and 0.481. The models achieved AUCs of 0.849, 0.908, and 0.912, with Brier scores of 0.128, 0.105, and 0.104, log losses of 0.409, 0.349, and 0.345, and calibration-in-the-large of 0.058, 0.054, and 0.051, respectively. Among these, the Random Forest model demonstrated superior performance. CONCLUSIONS: The research indicates that obesity in steelworkers results from a combination of occupational and lifestyle factors. Of the models tested, the Random Forest model exhibited superior predictive ability, highlighting its significant practical application.

Analysis of factors affecting nonalcoholic fatty liver disease in Chinese steel workers and risk assessment studies.

BACKGROUND: The global incidence of nonalcoholic fatty liver disease (NAFLD) is rapidly escalating, positioning it as a principal public health challenge with significant implications for population well-being. Given its status as a cornerstone of China's economic structure, the steel industry employs a substantial workforce, consequently bringing associated health issues under increasing scrutiny. Establishing a risk assessment model for NAFLD within steelworkers aids in disease risk stratification among this demographic, thereby facilitating early intervention measures to protect the health of this significant populace. METHODS: Use of cross-sectional studies. A total of 3328 steelworkers who underwent occupational health evaluations between January and September 2017 were included in this study. Hepatic steatosis was uniformly diagnosed via abdominal ultrasound. Influential factors were pinpointed using chi-square (χ2) tests and unconditional logistic regression analysis, with model inclusion variables identified by pertinent literature. Assessment models encompassing logistic regression, random forest, and XGBoost were constructed, and their effectiveness was juxtaposed in terms of accuracy, area under the curve (AUC), and F1 score. Subsequently, a scoring system for NAFLD risk was established, premised on the optimal model. RESULTS: The findings indicated that sex, overweight, obesity, hyperuricemia, dyslipidemia, occupational dust exposure, and ALT serve as risk factors for NAFLD in steelworkers, with corresponding odds ratios (OR, 95% confidence interval (CI)) of 0.672 (0.487-0.928), 4.971 (3.981-6.207), 16.887 (12.99-21.953), 2.124 (1.77-2.548), 2.315 (1.63-3.288), 1.254 (1.014-1.551), and 3.629 (2.705-4.869), respectively. The sensitivity of the three models was reported as 0.607, 0.680 and 0.564, respectively, while the precision was 0.708, 0.643, and 0.701, respectively. The AUC measurements were 0.839, 0.839, and 0.832, and the Brier scores were 0.150, 0.153, and 0.155, respectively. The F1 score results were 0.654, 0.661, and 0.625, with log loss measures at 0.460, 0.661, and 0.564, respectively. R2 values were reported as 0.789, 0.771, and 0.778, respectively. Performance was comparable across all three models, with no significant differences observed. The NAFLD risk score system exhibited exceptional risk detection capabilities with an established cutoff value of 86. CONCLUSIONS: The study identified sex, BMI, dyslipidemia, hyperuricemia, occupational dust exposure, and ALT as significant risk factors for NAFLD among steelworkers. The traditional logistic regression model proved equally effective as the random forest and XGBoost models in assessing NAFLD risk. The optimal cutoff value for risk assessment was determined to be 86. This study provides clinicians with a visually accessible risk stratification approach to gauge the propensity for NAFLD in steelworkers, thereby aiding early identification and intervention among those at risk.

A nested case-control study of the effects of dust exposure, smoking on COPD in coal workers.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) represents a prevalent ailment, progressively surging within the ranks of coal mine laborers. The current study endeavors to elucidate the effects of dust exposure and smoking on COPD incidence amongst coal mine workers, while concurrently devising preventive strategies for this affliction. METHOD: A nested case-control study was conducted encompassing 1,416 participants aged ≥ 18 years, spanning the duration from (2017-2018) until 2020. A meticulous matching process yielded a cohort of 708 COPD patients, each paired with a control subject, forming a harmonious 1:1 ratio. Multiple logistic regression analysis was employed to scrutinize the associations between smoking, dust exposure with COPD among coal workers. RESULTS: The COPD prevalence within the cohort of coal workers under investigation amounted to 22.66%, with an accompanying incidence density of 0.09/person-year. Following meticulous adjustment for confounding variables, it was discerned that cumulative dust exposure within the range of 47.19 ~ (OR: 1.90, 95% CI: 1.05, 3.44), 101.27 ~ (OR: 1.99, 95% CI: 1.17, 3.39), as well as smoking indices of 72 ~ (OR: 1.85, 95% CI: 1.19, 2.88), 145 ~ (OR: 1.74, 95% CI: 1.17, 2.61), 310 ~ (OR: 1.85, 95% CI: 1.23, 2.77) engender an escalated vulnerability to COPD among coal workers. Furthermore, interaction analysis discerned an absence of both multiplicative and additive interactions between dust exposure, smoking, and COPD occurrence amidst coal workers. CONCLUSION: Dust exposure and smoking were unequivocally identified as precipitating risk factors for COPD incidence within the population of coal workers, albeit devoid of any discernible interaction between these two causal agents.

Achieving Near-unity Photoluminescence Quantum Yields in Organic-Inorganic Hybrid Antimony (III) Chlorides with the [SbCl5 ] Geometry.

Hybrid organic-inorganic antimony halides have attracted increasing attention due to the non-toxicity, stability, and high photoluminescence quantum yield (PLQY). To shed light on the structural factors that contribute to the high PLQY, five pairs of antimony halides with general formula A2 SbCl5 and A2 Sb2 Cl8 are synthesized via two distinct methods and characterized. The A2 SbCl5 type adopts square pyramidal [SbCl5 ] geometry with near-unity PLQY, while the A2 Sb2 Cl8 adopts seesaw dimmer [Sb2 Cl8 ] geometry with PLQY≈0 %. Through combined data analysis with the literature, we have found that A2 SbCl5 series with square pyramidal geometry generally has much longer Sb⋅⋅⋅Sb distances, leading to more expressed lone pairs of SbIII . Additional factors including Sb-Cl distance and stability of antimony chlorides may also affect PLQY. Our targeted synthesis and correlated insights provide efficient tools to precisely form highly emissive materials for optoelectronic applications.

Turn-on Circularly Polarized Luminescence in Chiral Indium Chlorides by 5s2 Metal Centers.

Introducing chirality into the metal-halide hybrids has enabled many emerging properties including chiroptical activity, spin-dependent transport, and ferroelectricity. However, most of the chiral metal-halide hybrids to date are non-emissive, and the underlying mechanism remains elusive. Here, we show a new strategy to turn on the circularly polarized luminescence (CPL) in chiral metal-halide hybrids. We demonstrate that alloying Sb3+ into chiral indium-chloride hybrids dramatically increases the photoluminescence quantum yield in two new series of chiral indium-antimony chlorides. These materials exhibit strong CPL signals with tunable energy and a high dissymmetry factor up to 1.5×10-2 . Mechanistic studies reveal that the emission originates from the self-trapped excitons centered in 5s2 Sb3+ . Moreover, near-ultraviolet pumped white light is demonstrated with a polarization up to 6.0 %. Our work demonstrates new strategies towards highly luminescent chiral metal-halide hybrids.

Rashba Band Splitting and Bulk Photovoltaic Effect Induced by Halogen Bonds in Hybrid Layered Perovskites.

Non-covalent interactions play an essential role in directing the self-assembly of hybrid organic-inorganic crystals. In hybrid halide perovskites, hydrogen bonding has been the paramount non-covalent interaction. Here, we show another non-covalent interaction, namely, the halogen bond interaction, that directs a symmetry-breaking assembly in a new series of two-dimensional (2D) perovskites (ICH2 CH2 NH3 )2 (CH3 NH3 )n-1 Pbn I3n+1 (n is the layer thickness, n=1-4). Structural analysis shows that the halogen bond strength varies with the layer thickness. For the odd number (n=1, 3) layered perovskites, stronger halogen interaction leads to centrosymmetric structures, whereas for the n=2 layered perovskites, weaker halogen bonds result in non-centrosymmetric structures. Transient reflection spectroscopy shows a suppressed radiative recombination rate (k2 ≈0) and prolonged spin lifetime for n=2 structure, suggesting an enhanced Rashba band splitting effect. The structural asymmetry is further confirmed with a reversible bulk photovoltaic effect. Our work provides a new design strategy to enable hybrid perovskites with emerging properties and functionalities associated with structural asymmetry.

Revealing the Intrinsic Chiroptical Activity in Chiral Metal-Halide Semiconductors.

The combination of chirality and semiconducting properties has enabled chiral metal-halide semiconductors (MHS) to be promising candidates for spin- and polarization-resolved optoelectronic devices. Although several chiral MHS with rich chemical and structural diversity have been reported lately, the macroscopic origin of chiroptical activity remains elusive. Here, combining spectroscopic measurements and Mueller matrix analysis, we discover that the previously reported "apparent" anisotropy factor measured from circular dichroism (CD) in chiral MHS thin films is not an intrinsic chiroptical property, but rather, arising from an interference between the film's linear birefringence (LB) and linear dichroism (LD). We verify the presence of LB and LD effects in both one-dimensional and zero-dimensional chiral MHS thin films. We establish spectroscopic methods to decouple the genuine CD from other spurious contributions, which allows a quantitative comparison of the intrinsic chiroptical activity across different chiral MHS. The relationship between the structure and the genuine chiroptical activity is then uncovered, which is well described by the chirality-induced spin-orbit coupling in the chiral structures. Our study unveils the macroscopic origin of chiroptical activity of chiral MHS and provides design principles for obtaining high anisotropic factors for future chiral optoelectronic applications.

Expanding the absorption and photoresponse of 1D lead-halide perovskites via ultrafast charge transfer.

Low-dimensional metal halide perovskites are attracting extensive attention due to their enhanced quantum confinement and stability compared to three-dimensional perovskites. However, low dimensional connectivity in the inorganic frameworks leads to strongly bounded excitons with limited absorption properties, which impedes their application in photovoltaic devices. Here, we show that, by incorporating a strong electron accepting methylviologen cation, charge transfer (CT) at the organic/inorganic interface can effectively tune the optical properties in one-dimensional (1D) lead-halide perovskites. Both 1D MVPb2I6 and MVPb2Br6 display expanded absorption and photoresponse activity compared to CT inactive cations. The photoinduced CT process in MVPb2I6 was further characterized by transient absorption spectroscopy, which shows an ultrafast CT process within 1 ps, generating charge separated states. Our work unveils the interesting photophysics of these unconventional 1D perovskites with functional organic chromophores.

Tuning Spin-Polarized Lifetime in Two-Dimensional Metal-Halide Perovskite through Exciton Binding Energy.

Metal-halide perovskite semiconductors have attracted attention for opto-spintronic applications where the manipulation of charge and spin degrees of freedom have the potential to lower power consumption and achieve faster switching times for electronic devices. Lower-dimensional perovskites are of particular interest since the lower degree of symmetry of the metal-halide connected octahedra and the large spin-orbit coupling can potentially lift the spin degeneracy. To achieve their full application potential, long spin-polarized lifetimes and an understanding of spin-relaxation in these systems are needed. Here, we report an intriguing spin-selective excitation of excitons in a series of 2D lead iodide perovskite (n = 1) single crystals by using time- and polarization-resolved transient reflection spectroscopy. Exciton spin relaxation times as long as ∼26 ps at low excitation densities and at room temperature were achieved for a system with small binding energy, 2D EOA2PbI4 (EOA = ethanolamine). By tuning the excitation density and the exciton binding energy, we identify the dominant mechanism as the D'yakonov-Perel (DP) mechanism at low exciton densities and the Bir-Aronov-Pikus (BAP) mechanism at high excitation densities. Together, these results provide new design principles to achieve long spin lifetimes in metal-halide perovskite semiconductors.

Experimental demonstration of an ultra-thin radar-infrared bi-stealth rasorber.

We propose a radar-infrared bi-stealth rasorber that not only provides broad microwave absorptivity and low infrared emissivity but also possesses a microwave transmission window at low frequency. It is composed of three functional layers, which are carefully designed to independently control the infrared emission, microwave absorption, and transmission, respectively. The structure exhibits broadband (8.1-19.3 GHz) and high-efficiency (>90%) absorption. A transmission window appears at low frequency with a transmission peak of 80% at 2.68 GHz. The thermal emissivity of the structure is about 0.27 in the atmosphere window, which is close to that of metal. Moreover, the total thickness of the proposed structure is only 3.713 mm. The low-infrared-emissivity, high-microwave-absorption and frequency-selective-transmission properties promise it will find potential applications in various stealth fields.

Spin-Valley Locking Effect in Defect States of Monolayer MoS2.

Valley pseudospin in two-dimensional (2D) transition-metal dichalcogenides (TMDs) allows optical control of spin-valley polarization and intervalley quantum coherence. Defect states in TMDs give rise to new exciton features and theoretically exhibit spin-valley polarization; however, experimental achievement of this phenomenon remains challenges. Here, we report unambiguous valley pseudospin of defect-bound localized excitons in CVD-grown monolayer MoS2; enhanced valley Zeeman splitting with an effective g-factor of -6.2 is observed. Our results reveal that all five d-orbitals and the increased effective electron mass contribute to the band shift of defect states, demonstrating a new physics of the magnetic responses of defect-bound localized excitons, strikingly different from that of A excitons. Our work paves the way for the manipulation of the spin-valley degrees of freedom through defects toward valleytronic devices.

Highly Distorted Chiral Two-Dimensional Tin Iodide Perovskites for Spin Polarized Charge Transport.

Incorporating chiral organic molecules into organic/inorganic hybrid 2D metal-halide perovskites results in a novel family of chiral hybrid semiconductors with unique spin-dependent properties. The embedded chiral organic moieties induce a chiroptical response from the inorganic metal-halide sublattice. However, the structural interplay between the chiral organic molecules and the inorganic sublattice, as well as their synergic effect on the resulting electronic band structure need to be explored in a broader material scope. Here we present three new layered tin iodide perovskites templated by chiral (R/S-)methylbenzylammonium (R/S-MBA), i.e., (R-/S-MBA)2SnI4, and their racemic phase (rac-MBA)2SnI4. These MBA2SnI4 compounds exhibit the largest level of octahedral bond distortion compared to any other reported layered tin iodide perovskite. The incorporation of chiral MBA cations leads to circularly polarized absorption from the inorganic Sn-I sublattice, displaying chiroptical activity in the 300-500 nm wavelength range. The bandgap and chiroptical activity are modulated by alloying Sn with Pb, in the series of (MBA)2Pb1-xSnxI4. Finally, we show that vertical charge transport through oriented (R-/S-MBA)2SnI4 thin films is highly spin-dependent, arising from a chiral-induced spin selectivity (CISS) effect. We demonstrate a spin-polarization in the current-voltage characteristics as high as 94%. Our work shows the tremendous potential of these chiral hybrid semiconductors for controlling both spin and charge degrees of freedom.

Sensitizing Singlet Fission with Perovskite Nanocrystals.

The marriage of colloidal semiconductor nanocrystals and functional organic molecules has brought unique opportunities in emerging photonic and optoelectronic applications. Traditional semiconductor nanocrystals have been widely demonstrated to initiate efficient triplet energy transfer at the nanocrystal-acene interface. Herein, we report that unlike conventional semiconductor nanocrystals, lead halide perovskite nanocrystals promote an efficient Dexter-like singlet energy transfer to surface-anchored pentacene molecules rather than triplet energy transfer. Subsequently, molecular pentacene triplets are efficiently generated via singlet fission on the nanocrystal surface. Our demonstrated strategy not only unveils the obscure energy dynamics between perovskite nanocrystal and acenes, but also brings important perspectives of utilizing singlet fission throughout the solar spectrum.

Enhanced Charge Transport in 2D Perovskites via Fluorination of Organic Cation.

Organic-inorganic halide perovskites incorporating two-dimensional (2D) structures have shown promise for enhancing the stability of perovskite solar cells (PSCs). However, the bulky spacer cations often limit charge transport. Here, we report on a simple approach based on molecular design of the organic spacer to improve the transport properties of 2D perovskites, and we use phenethylammonium (PEA) as an example. We demonstrate that by fluorine substitution on the para position in PEA to form 4-fluorophenethylammonium (F-PEA), the average phenyl ring centroid-centroid distances in the organic layer become shorter with better aligned stacking of perovskite sheets. The impact is enhanced orbital interactions and charge transport across adjacent inorganic layers as well as increased carrier lifetime and reduced trap density. Using a simple perovskite deposition at room temperature without using any additives, we obtained a power conversion efficiency of >13% for (F-PEA)2MA4Pb5I16-based PSCs. In addition, the thermal stability of 2D PSCs based on F-PEA is significantly enhanced compared to those based on PEA.

Degradable and Thermosensitive Microgels Synthesized via Simultaneous Quaternization and Siloxane Condensation.

Degradable and thermosensitive microgels were successfully prepared via simultaneous quaternization and siloxane condensation during surfactant-free emulsion polymerization, with N-vinylcaprolactam as the main monomer and 1-vinylimidazole (VIM) as the comonomer, in the presence of (3-bromopropyl)trimethoxysilane (BPTMOS). The formation mechanism of cross-linking network was attributed to the hydrolysis and condensation of the methoxysilyl groups of BPTMOS and the quaternization of imidazole moiety of VIM by the bromine group of BPTMOS, leading to the microgels. The microgels were spherical in shape with a narrow size distribution, stable in an acidic buffer solution, but degradable in neutral and alkaline solutions. The presence of quaternized imidazolium in the same chain segment of Si-O-Si cross-linking points promoted the decomposition of Si-O-Si bonds and hence the degradation of the microgels. The obtained microgels could load and release the model drug, doxorubicin. The size, thermosensitivity, stability, degradation rate, and drug release behavior of the resultant microgels could be tuned by controlling the cross-linking degree, chemical composition, and degradation medium.

Enhanced photoredox activity of CsPbBr3 nanocrystals by quantitative colloidal ligand exchange.

Quantitative colloidal ligand exchange on lead-halide perovskite nanocrystals (NCs) has remained a challenge due to the dynamic passivation of amines and carboxylic acids and the instability of core lead-halide perovskite systems. Here, we present a facile colloidal ligand exchange process using cinnamate acid ligands to quantitatively displace native oleate ligands on CsPbBr3 NCs. The short cinnamate ligands lead to a 23-fold enhancement of the electron-donating ability of the CsPbBr3 NCs when benzoquinone is used as an electron acceptor. A significantly increased photoredox activity is also observed in a complete photocatalytic reaction: the α-alkylation of aldehydes. Our results provide a new strategy to tune the photoredox activity of halide perovskite NCs as well as the exploration of NC-ligand interactions.