Donor Character Research Articles

NHC Core Phosphonium Ylide-based Palladium(II) Pincer Complexes: The Second Ylide Extremity Makes the Difference.

The coordinating properties of N-heterocyclic carbene (NHC) (A), phenolate (B), and phosphonium ylide (C) moieties were investigated systematically through the preparation of a family of NHC, phosphonium ylide-based pincer ligands, where the third donor extremity can be either an NHC, a phenolate, or a phosphonium ylide. The overall donor character of such ligands [NHC(AaBbCc)] (a + b + c = 2) was analyzed by comparison of the molecular orbitals (energy and shape), oxidation potentials (Epox), and IR νCO and νCN stretching frequencies of their isostructural pincer Pd(II) complexes [NHC(AaBbCc)PdL][OTf] (L = NCCH3, CO, or CNtBu). The three categories of pincer complexes based on phosphonium ylides were easily obtained by acidic treatment of their highly stable ortho-metalated Pd(II) precursors prepared in a single step from readily available N-phosphonio-substituted imidazolium salts. Analysis of IR data indicated that NHC and phenolate ligands have a similar donor character but which remains lower than that of the phosphonium ylide. The impact on catalytic performance of the incorporation of a second strongly donating phosphonium ylide into the ligand architecture was illustrated in the Pd-catalyzed allylation of aldehydes.

Investigation of Optical and Electrochemical Properties of Benzene Based Solution Processable 2,1,3-Benzooxadiazole Comprising Polymers

Four novel solution processable benzooxadiazole containing alternating copolymers namely poly (5,6-bis(octyloxy)-4-(5-phenylthiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]oxadiazole)PBOTPh, poly (5,6-bis(octyloxy)-4-(5-phenylselenophen-2-yl)-7-(selenophen-2-yl)benzo[c][1,2,5]oxadiazole)PBOSPh, poly (4-(furan-2-yl)-5,6-bis(octyloxy)−7-(5-phenylfuran-2-yl)benzo[c][1,2,5]oxadiazole)PBOFPh and poly (5,6-bis(octyloxy)-4-(5-phenylthieno[3,2-b]thiophen-2-yl)-7-(thieno[3,2-b]thiophen-2-yl)benzo[c][1,2,5]oxadiazole) PBOTTPh incorporating 5,6-bis(octyloxy)benzo[c][1,2,5]oxadiazole as the acceptor moiety and benzene as the donor moiety were synthesized via Suzuki polycondensation reaction. Various electron donor moieties were used as π bridges in the polymer backbone to tailor the optoelectronic properties of the polymers. To explore the electrochemical and electrochromic properties and the photovoltaic properties of the copolymers, cyclic voltammetry, spectroelectrochemistry and kinetic studies were conducted. Thiophene, selenophene, furan and thienothiophene π bridges were incorporated into the polymer backbones. Thiophene and selenophene based alternating copolymers showed purple color in its neutral state whereas furan and thienothiophene bearing copolymers have pinkish purple and dark purple in their neutral states respectively. The optical band gaps of the polymers were calculated as 1.85, 1.76, 1.58, 1.79 eV for thiophene, selenophene, thienothiophene and furan based copolymers, respectively. Among all the alternating copolymers, the lowest optical band gap corresponds to thienothiophene comprising alternating copolymer which is 1.58 eV and red shifted in absorption due to the stronger donor character compared to other analogs. HOMO and LUMO levels were calculated from cyclic voltammetry studies using onsets of oxidation and reduction, respectively. HOMO levels were calculated as −5.96 eV for PBOTPh, −5.85 eV for PBOSPh, −5.63 eV for PBOTTPh and −5.74 eV for PBOFPh. LUMO levels were determined as −4.02 eV for PBOSPh, −4.03 eV for PBOTTPh and −3.87 eV for PBOFPh. Bulk heterojunction (BHJ) polymer solar cells based on selenophene containing polymer were fabricated. The device architecture was: ITO/PEDOT:PSS/PBOSPh:PC71BM/Ca/Al. After optimization studies, best results for 130 nm thickness, Polymer:PC71BM with 1:2 ratio, Voc, Jsc, FF, PCE (%) were found as 0.62 V, 4.53 mA cm−2, 0.58, 1.63% under illumination of AM 1.5 G 100 mW cm−2.

A near-infrared fluorescent probe with an improved Stokes shift achieved by tuning the donor–acceptor–donor character of the rhodamine skeleton and its applications

In this paper, we report a novel near-infrared (NIR) mitochondrion-targeted fluorescent probe, RQS, with an improved Stokes shift (96 nm) for the specific detection of mitochondrial mercury ion (Hg2+) because mitochondrion is one of the main targeted organelles of Hg2+. For the preparation of the probe, a novel asymmetrical fluorescent xanthene dye RQ was first synthesized by tuning the donor–acceptor–donor (D–A–D) character of the rhodamine skeleton, and then the probe RQS was constructed by the mechanism of mercury-promoted ring-opening reaction. As expected, RQS could be used for the specific detection of Hg2+ with high selectivity, high sensitivity, and a detection limit down to the nanomolar range (2 nM). Importantly, RQS is capable of specifically distributing in mitochondria, and thus detect Hg2+ in real-time and provided a potential tool for studying the cytotoxic mechanisms of Hg2+.

Exploring Soft Donor Character of the N-2-Pyrazinylmethyl Group by Coordinating Trivalent Actinides and Lanthanides Using Aminopolycarboxylates.

The trivalent f-element coordination chemistry of a novel aminopolycarboxylate complexant was investigated. The novel reagent is an octadentate complexant that resembles diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA), but a single N-acetate pendant arm was substituted with a N-2-pyrazinylmethyl functional group. Thermodynamic studies of ligand protonation and trivalent lanthanide, americium and curium, complexation by N-2-pyrazinylmethyldiethylenetriamine-N,N',N″,N″-tetraacetic acid (DTTA-PzM) emphasize the strong electron withdrawing influence of the N-2-pyrazinylmethyl group. Specifically, DTTA-PzM is more acidic compared to a N-2-pyridinylmethyl-substituted structural equivalent, DTTA-PyM, with a substantial lowering of pK7, corresponding to the protonation of a second aliphatic amine site. The participation of the pyrizyl nitrogen in the metal ion coordination sphere is evident from the fluorescence lifetime decay measurements of metal hydration and the interpretation of the stability constants for ML- and MHL(aq) complexes. The overall conditional stability constants for the trivalent f-element complexation by DTTA-PzM complexes decrease, relative to DTTA-PyM, as expected based on the lower basicity of pyrazine in water relative to pyridine. Replacement of the N-2-pyridinylmethyl group with N-2-pyrazinylmethyl, while enhancing the total acidity of DTTA-PzM, also reduces its softness, as manifested by a small lowering of β101Am/Nd and liquid-liquid separation of trivalent lanthanides from trivalent americium. Despite this, the 4f/5f separation is doubled when DTTA-PzM replaces DTPA as an aqueous complexant in solvent extraction.

Theoretical Assessment of the Second-Order Nonlinear Optical Responses of Lindqvist-Type Organoimido Polyoxometalates.

The second-order nonlinear optical properties of Lindqvist-type organoimido polyoxometalates bearing donor and acceptor substituents are evaluated by employing density functional theory and time-dependent density functional theory using the ωB97X-D range-separated hybrid exchange-correlation functional to describe accurately the field-induced effects. The hyper-Rayleigh scattering responses, βHRS (-2ω; ω, ω), and the depolarization ratio are the targeted quantities. They are analyzed by resorting to the two-state model, which reduces the full summation-over-state expression to a single diagonal term and relates the response to a few spectroscopic quantities. The validity of this model is demonstrated by its ability to reproduce the βHRS variations as a function of the nature of the ligand, owing to the dominant 1D character of these organic-inorganic hybrids. The calculated values are in good agreement with the recent experimental work of Al-Yasari et al. (Inorg. Chem. 2017, 56, 10181-10194), which demonstrates that the hexamolybdate moiety plays the role of an electron acceptor group. On the contrary, they contradict previous studies, which attributed an electron donor character to the polyoxometalate moiety. Calculations highlight that (i) combining the hexamolybdate unit with an organic ligand bearing a strong donor substituent leads to an enhanced first hyperpolarizability, associated with a dominant low-energy excited state, characterized by a large excitation-induced electron transfer from the donating ligand to the hexamolybdate, therefore coupling the polyoxometalate (POM) and its substituted ligand; (ii) in the case of weaker donor substituents, the hexamolybdate still behaves as an electron acceptor, but the first hyperpolarizability is smaller and the coupling has a reduced spatial extension; and, on the contrary, (iii) in the presence of an acceptor substituent, there is a competition between the hexamolybdate and this group so that the first hyperpolarizability becomes very small. The whole set of results demonstrates that polyoxometalate moieties are good candidates to achieve large second-order nonlinear optical (NLO) responses while keeping a rather large transparency window and also that there remains space to improve their integration into NLO efficient organic-inorganic hybrids.

Chloranilato-Based Layered Ferrimagnets with Solvent-Dependent Ordering Temperatures

We report the synthesis and the characterization of six new heterometallic chloranilato-based ferrimagnets formulated as (NBu4)[MnCr(C6O4Cl2)3]·nG with n = 1 for G = C6H5Cl (1), C6H5I (3), and C6H5CH3 (4); n = 1.5 for G = C6H5Br (2) and n = 2 for G = C6H5CN (5) and C6H5NO2 (6); (C6O4Cl2)2− = 1,3-dichloro,2,5-dihydroxy-1,4-benzoquinone dianion. The six compounds are isostructural and show hexagonal honeycomb layers of the type [MnCr(C6O4Cl2)3]− alternating with layers containing the NBu4+ cations. The hexagons are formed by alternating Mn(II) and Cr(III) connected by bridging bis-bidentate chloranilato ligands. The benzene derivative solvent molecules are located in the hexagonal channels (formed by the eclipsed packing of the honeycomb layers) showing π-π interactions with the anilato rings. The six compounds behave as ferrimagnets with ordering temperatures in the range 9.8–11.2 K that can be finely tuned by the donor character of the benzene ring and by the number of solvent molecules inserted in the hexagonal channels. The larger the electron density on the aromatic ring and the larger the number of solvent molecules are, the higher Tc is. The only exception is provided by toluene, where the formation of H-bonds might be at the origin of weaker π-π interactions observed in this compound.

Homo- and Copolymerization of Ethylene with Norbornene Catalyzed by Vanadium(III) Phosphine Complexes.

Herein, we report the homo- and co-polymerization of ethylene (E) with norbornene (NB) catalyzed by vanadium(III) phosphine complexes of the type VCl3(PMenPh3-n)2 [n = 2 (1a), 1 (1b)] and VCl3(PR3)2 [R = phenyl (Ph, 1c), cyclohexyl (Cy, 1d), tert-butyl (tBu, 1e)]. In the presence of Et2AlCl and Cl3CCOOEt (ETA), 1a–1e exhibit good activities for the polymerization of ethylene, affording linear, semicrystalline PEs with a melting temperature of approximately 130 °C. Mainly alternating copolymers with high comonomer incorporation were obtained in the E/NB copolymerization. A relationship was found between the electronic and steric properties of the phosphine ligands and the catalytic performance. Overall, the presence of electron-withdrawing ligand substituents increases the productivity, complexes with aryl phosphine (weaker σ–donor character) exhibiting a higher (co)polymerization initiation rate than those with alkyl phosphines (stronger σ–donor character). Steric effects also seem to play a key role since 1d and 1e, having large size phosphines (PCy3 θ = 170° and PtBu3 θ = 182°, respectively) are more active than 1a (PMe2Ph θ = 122°). In this case, the larger size of PtBu3 and PCy3 likely compensates for their higher donor strength compared to PMe2Ph.

Blue TADF Emitters Based on Indenocarbazole Derivatives with High Photoluminescence and Electroluminescence Efficiencies.

A series of blue thermally activated delayed fluorescence (TADF) emitters were designed and synthesized using 2,4,6-triphenyl-1,3,5-triazine as the acceptor unit and indenocarbazole derivatives as the electron-donating moiety. In contrast with other six-membered heterocycles, like phenothiazine, phenoxazine, and dihydroacridine, where the TADF efficiency is affected by the presence of different conformers, indenocarbazole derivatives do not show this effect. Therefore, InCz23FlTz, InCz23DPhTz, InCz23DMeTz, and InCz34DPhTz allow the investigation of the effect of different substituents and substitution positions on TADF properties, without the influence of different conformations. We have demonstrated that the substituted position on the carbazole and different substituents in the same position have clear influence on the donor character of indenocarbazole derivatives. Also, the color purity of blue emission and excited states could be adjusted by substituents and substituted position, and thus excellent blue emitters can be obtained. Besides, the four compounds show relatively small TADF contribution under optical excitation; however, excellent performances are obtained in the electroluminescent devices, especially with InCz34DPhTz, which shows a maximum external quantum efficiency of around 26%. In the end, we find an effective way to design high-efficiency blue TADF materials and deeply study the relation between the structure and property in indenocarbazole derivatives.

Efficiency enhancement of iridium-based organometallic light emitting diodes

The efficiency of the Organic Light Emitting Diode (OLED) is given either by the internal quantum efficiency of the organometallic compound or by the charge transport across OLED. IrQ(ppy)2 is a new organometallic compound which gives green and red electroluminescence. This dual emitter compound exhibits a lower internal quantum efficiency compared with classical Ir(ppy)3 green emitter because of a weak coupling between Ir3+ and oxygen ions which significantly reduces the charge transfer towards quinoline ligand. This lower internal quantum efficiency is compensated by the higher electron donor character of the quinoline ligand which induces better change transport in OLED structures. In the case of Ir(ppy)3 green emitter, the efficiency can be improved by adding magnetic or metallic nanoparticles which significantly change the charge transport for the Ir(ppy)3 based OLED structures. The metallic or magnetic nanoparticles embedded in the transparent and conductive polymer, reduce the electron injection, acting as filling traps, which directly increases the electroluminescence and the current at the same voltage.

Synthesis and Catalytic Activity of Iron Hydride Ligated with Bidentate N-Heterocyclic Silylenes for Hydroboration of Carbonyl Compounds

We report the synthesis of a novel bidentate N-heterocyclic silylene (NHSi) ligand, N-(LSi:)-N-methyl-2-pyridinamine (1) (L = PhC(NtBu)2), and the first bischelate disilylene iron hydride, [(Si,N)(Si,C)Fe(H)(PMe3)] (2), and monosilylene iron hydride, [(Si,C)Fe(H)(PMe3)3] (2′), through Csp2–H activation of the NHSi ligand. Compounds 1 and 2 were fully characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. Density functional theory calculations indicated the multiple-bond character of the Fe–Si bonds and the π back-donation from Fe(II) to the Si(II) center. Moreover, the strong donor character of ligand 1 enables 2 to act as an efficient catalyst for the hydroboration reaction of carbonyl compounds at room temperature. Chemoselective hydroboration is attained under these conditions. This might be the first example of hydroboration of ketones and aldehydes catalyzed by a silylene hydrido iron complex. A catalytic mechanism was suggested and partially experimentally verified.

(E)‐3‐X‐indoline‐2‐ones as potent and selective inhibitors against different receptor tyrosine kinase (RTKs) in solution vs gas phase, at DFT

AbstractUsing DFT SCRF calculations, we have evaluated the solvent effects on the structure, stability, and electronic properties of biologically active compounds as (E)‐3‐X‐indoline‐2‐one derivatives (X = phenyl, furan‐2‐yl, 1H‐pyrrol‐2‐yl, and thiophen‐2‐yl, I‐IV, respectively) in six solvents. These solvents differ in their polarity with the dielectric constants varying from 2.2 to 78.5 including benzene, C2H4Cl2, EtOH, H2O, nitromethane, and DMSO. Moreover, two of them have a hydrogen‐bond donor character. All possible hydrogen‐bonding in the water solution with oxygen and nitrogen atoms as hydrogen‐acceptor centers in indoline‐2‐ones derivatives, I‐IV, have been considered in our studies. The stability of each solute (I‐IV) depends on the dielectric constant of the solvent and the possibility of the hydrogen bonding. Moreover, the highest observed solvent‐gas phase energy gaps (∆Es‐g) relate to structure III in water, whereas the lowest ∆Es‐g is associated with II in benzene. Thus, III is the most solvent sensitive and enjoys maximum stabilization in water. On the other extreme, II is the least solvent sensitive, and its stability is the least affected by salvation in benzene. Forbidden concerted [1,6] and [1,3]‐H shift mechanisms are suggested for the ketone III―III′, III′′ enole tautomerizations in gas phase, while allowed step‐by‐step [1,6] and [1,3]‐H shifts are proposed for tautomerization in water.

Cyclopropenium Enhanced Thiourea Catalysis.

An integral part of modern organocatalysis is the development and application of thiourea catalysts. Here, as part of our program aimed at developing cyclopropenium catalysts, the synthesis of a thiourea-cyclopropenium organocatalyst with both cationic hydrogen-bond donor and electrostatic character is reported. The utility of the this thiourea organocatalyst is showcased in pyranylation reactions employing phenols, primary, secondary, and tertiary alcohols under operationally simple and mild reaction conditions fora broad substratescope. The addition of benzoic acid as a co-catalyst facilitating cooperative Brønsted acid catalysis was found to be valuable for reactions involving phenols andhigher substituted alcohols. Mechanistic investigations, including kinetic and 1H NMR binding studies in conjunction with density function theory calculations, are described that collectively support a Brønsted acid mode of catalysis.

Electronic structure and migration of interstitial hydrogen in the rutile phase of TiO2

The formation and migration energies of interstitial hydrogen in rutile TiO2 are obtained from first principles calculations. The computational approach was based on density functional theory with a semilocal generalised-gradient approximation functional, supplemented with an on-site Hubbard term to account for correlation among the Ti 3d electrons. Charge-transition levels are calculated and compared to previous theoretical studies. The donor character of hydrogen is examined in depth, focusing in particular on the tendency to form polaron-like configurations with the unpaired electron trapped at nearby titanium ions. Distinct minimum-energy paths of hydrogen migration and associated energy barriers were determined by the nudged elastic-band method. The present findings show clearly the strong anisotropy in the energy barriers for migration within the open c channels as opposed to migration crossing adjacent channels of the rutile lattice. For the rate-limiting step which leads to macroscopic diffusion along the c axis the corresponding rate and diffusion coefficient were also determined from transition-state theory. The results are discussed in connection to existing measurements of hydrogen diffusion and recent findings from electron paramagnetic resonance, electron–nuclear double resonance and muonium spectroscopies that probed the spatial localization of the electron spin.

Self-healing epoxy nanocomposites via reversible hydrogen bonding

The development of high performance self-healing composites is still at an early stage due to the difficulty to integrate self-healing mechanisms in their structure by applying current manufacturing processes. Here, the authors propose structural self-healing resins based on dynamic hydrogen bonds capable to overcome many current industrial limitations. Hydrogen bonding moieties, such as barbiturate and thymine, able to act as reversible healing-elements by their simultaneous donor and acceptor character, can be covalently linked to multi-wall carbon nanotubes (MWCNTs) to generate self-healing nanocomposites. The so functionalized MWCNTs, embedded in a rubber-toughened epoxy formulation, lead to reversible MWCNTs-bridges through the matrix due to strong attractive interactions between the rubber phase, finely dispersed in the matrix, and MWCNT walls. Healing efficiencies have been assessed for the nanocharged epoxy formulation loaded with 0.5% wt/wt of MWCNTs decorated with barbituric acid and thymine groups. For both functional groups, healing efficiencies higher than 50% have been found. Dynamic mechanical analysis (DMA) evidences an enhancement in epoxy chains movements due to micro/nano domains of the rubber phase enabling self-healing behavior by recovering the critical fracture load. Results from this study may promote the wide development of safe and cost-efficient self-healing composites in aeronautical, automotive, civil engineering and wind power industries.

Pillarquinones and Pillararenequinones

AbstractPillar[n]quinones and pillar[n‐m]arene[m]quinones are oxidation products of pillar[n]arenes. Their molecular structure resembles the parent compounds. However, their map of electron density is different. Each 1,4‐benzoquinone ring, which replaces a 1,4‐dialkoxy‐substituted benzene ring decreases the electron density in the interior cavity and increases the electron density on the upper and lower rim of the pillar. The electron donor character is stepwise transformed to an electron acceptor status. This effect alters the complexation tendencies, which are the most interesting properties of these macrocyclic host systems.

Tuning the molecular/electronic structure of new substituted pyrazoles: Synthesis, biological trials, theoretical approaches and Hammett correlations

The high yield synthesis, characterization and biological trials of a family of compounds containing the pyrazole core (E)-3,5-dimethyl-1-(4-R-phenyl)-4-(phenyldiazenyl)-1H-pyrazoles (with R = 4-CH3O (1), 4-CH3 (2), 4-H (3), 4-F (4), 4-Cl (5), 4-CF3 (6), 4-CN (7), 4-NO2 (8), 3-Cl (9), 3-NO2 (10), 2-Cl (11) and C6F5 (12)) are reported. Hammett correlations were found for the experimental and theoretical computed data, showing the dependence of all the obtained results on the donor or acceptor nature of the R substituent. In this sense, the absorption wavelength does decrease as the electron-withdrawing character of the substituent increases. Furthermore, the wavelength intensity does follow a Hammett correlation with the sigma donor character of the substituents. The compounds were characterized using MP, EA, UV–vis, FT-IR, 1H NMR, 13C NMR including bidimensional NMR experiments (HMBC and HMQC). The structures of 4, 5 and 8 were successfully elucidated by means of X-Ray diffraction. Pyrazole based dyes are known in pharmacological areas. Therefore, biological activity of all these structures were tested against cancer cell lines over a wide library of cell lines (60), including leukemia, colon and brain cancer, showing that the compounds have anticancer activity, which expands the knowledge of this kind of dyes as targets for this critical application. Finally, quantum calculations were carried out in order to give a rational explanation to the observed UV–vis absorption bands and FT-IR signals. As shown, it is possible to tune the molecular/electronic structure of the synthesized dyes by means of changing the R substituent in the structure.

Dimerization of Substituted Arylacetylenes-Quantum Chemical Calculations and Kinetic Studies.

The dimerization of substituted arylacetylenes is a very interesting tool to generate 1,3-butadiene 1,4-diradicals. Recently, it was shown that electron-withdrawing groups attached to the triple bond reduce the activation barrier and increase the stability of the diradical intermediates. Here, we investigate the influence of the π donor character of substituents, which are bound to the aryl system, on the dimerization reaction of arylacetylenes. Both quantum chemical calculations and kinetic studies reveal that the higher the π donor character of substituents, the lower the activation barrier. The highest observed difference between the model systems amounts to 4.0 kcal/mol, which represents an acceleration by a factor of 700. However, according to the calculations the π donor character of the substituents increases the diradical character of the intermediates.

Magnetic Hyperalkali Species of Gd-Based Clusters.

In this work, DFT calculations are performed in order to provide a basis for the assemblage of Gd-based supramolecular magnetic hyperalkali complexes that combine strong donor character and outstanding magnetic response. When the Gd atom is decorated with the lithiated superalkali moieties Li3O and Li4O, the calculated vertical ionization potential (VIP) is observed to drop to 3.75 eV for the Gd(Li3O)4 cluster, and 3.58 eV for the Gd(Li4O)3 cluster, which are below the VIP of cesium (3.99 eV) calculated at the same level of theory. A recipe earlier proposed for obtaining hyperalkali molecules is verified. By using the hypermetalated cluster Li4O in number that matches exactly the formal valence of Gd, we observe the lowest VIP, where the next excess electron provides the enhancement of the donor character besides stabilizing the cluster. The results indicate a new concept for designing highly reactive molecules.

Low pH optical sensor based on benzothiazole azo dyes

2-Amino-6-substituted benzothiazoles were obtained by a one-pot reaction of different anilines with thiocyanogen and used to prepare the respective 2-phenylazo-6-substituted-benzothiazoles in good yields by the classical diazotization reaction followed by coupling with two N,N-dialkylanilines. The aminobenzothiazoles 2a–d present absorption in the UV region, although the azo dyes 4a–e present absorption maxima in the visible region. In the aminobenzothiazoles and the respective azo dyes, changes in the donor and acceptor character of the substituents affect the absorption maxima. All electronic transitions were fully spin- and symmetry-allowed, with 1π-π* character. The aminobenzothiazoles 2a–d do not show significant fluorescence emission, while the azo dyes 4a–e presented very low fluorescence emission in the green-orange region. The azo dyes present large changes in the absorption spectra with changing pH (blue to red colour), suggesting their use as optical sensors for low pH values. Theoretical calculations were also performed to study the charge distribution and photophysical properties of the azo dyes in their ground and excited states, utilizing Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT). All calculations were carried out using PBE1PBE and ωB97XD functionals at the cc-pVDZ level for geometrical optimization, and at the jun-cc-pVTZ level for vertical transition energies and electronic property computations. Solvent effects were included by PCM formalism using acetonitrile and dichloromethane. Results were in good agreement with experimental data.

Inductive Effect of Nd for Ni3+ Stabilization in NdNiO3 Synthesized by Reactive DC Cosputtering

This work focus on the oxidation states of nickel in NdNiO3, Nd2NiO4, and NiOx thin films deposited by reactive magnetron sputtering. Thin films with a high Ni3+ content have been reached in the ternary oxides using a soft subsequent annealing in air. In order to understand the presence of Ni3+ oxidation state, the present work establishes a comparative study between the NiOx and Nd–Ni–Ox thin films deposited at room temperature in reactive conditions using different oxygen partial pressures. Crystallographic phases have been systematically identified by X-ray diffraction showing crystallized NiOx and amorphous thin films in the case of Ni and Nd cosputtering. The ionization state of Ni ions has been tracked by X-ray photoelectron spectroscopy. Analyses confirm the presence of Ni2+ in NiOx films whereas Ni3+ is systematically observed in Nd–Ni–Ox films highlighting the key role of Nd element during the deposition. The electron donor character of Nd3+ on Ni3+ via O 2p states by an inductive effect is clearly evidenced. This effect is strengthened by a strong difference in electronegativity between the rare earth (Re) and the transition metal (M). This concept is enlarged and faced with other ReMO3 perovskites, and their thermodynamic stability is discussed.