Weak Ligand Field Research Articles

Selecting the Optimal DFT Functionals for Reproducing the UV‐Vis Properties of Transition‐Metal Photocatalysts

AbstractWe have applied our practice‐oriented TDDFT benchmark strategy to assess the performance of pure, hybrid, range‐separated hybrid and double‐hybrid functionals for reproducing the electronic spectra of a set of 137 transition‐metal complexes. Our results enable simple pre‐screening of new transition‐metal based photocatalysts. The reference data is based on recently published measurements, from which we have established a new database. The database is named TMPHOTCAT‐137 to reflect the number of complexes (with Cu, Ru, Ir, Fe, Au, Mo and W centres) included and the fact that all of them are either proven or potential photocatalysts. We have found that the M06 functional is the best performer both in terms of practical accuracy and consistency for all metals except Fe. While B3LYP is similarly accurate for Ru and Ir complexes, for the rest of the metals significant wavelength scaling is necessary. Compared to our previous benchmark for organic photocatalysts, double‐hybrid functionals exhibit considerably poorer results while the range separated hybrids CAM−B3LYP and ωB97X−D offer the most consistent performance for both datasets. Among the metals, iron proved to be most difficult for TDDFT: even M06 predicts singlet‐singlet absorption spectra and quintet ground states erroneously, especially for weak ligand fields (i. e., only Fe−N bonds). The functionals that do not exhibit this behaviour are the pure (GGA, meta‐GGA) functionals, but the role of HF exchange in the spectral prediction is equivocal; while functionals with high amounts of HF exchange perform insufficiently, smaller amount of exact exchange yields overall better performance (M06, B3LYP). We have also shown that inclusion of spin‐orbit coupling for the heavier metals does not improve the results. The updated spectrum optimizer code, the TMPHOTCAT‐137 database and the Jupyter Notebook used for analysis are available at github.com/PeterF1234/spectrum_optimizer.

A fluorescent magnetic nanocrystalline cellulose nanosensor based on rhodamine B for Fe3+ ion detection

This research introduces a nanosensor specifically designed for the detection of Fe3+ ions in aqueous solutions. The sensor is created using magnetic nanoparticles that have been functionalized with rhodamine B (RB). The Z-average particle size was 235.8, 287.3, and 121.6 for NCC, NCC@Fe3O4, and NCC@Fe3O4@RB indicating successful mitigation of magnetic aggregation by NCC and RB. The resulting structure, NCC@Fe3O4@RB, acts as a fluorescent probe that emits strong fluorescence under ultraviolet light, demonstrating its potential as an efficient tool for Fe3+ ion detection in water. The NCC@Fe3O4@RB fluorescent probe had a limit of detection (LOD) of 1 × 10−5 M, with linearity at concentrations of 1 × 10−4–5 × 10−3 M. Upon introduction of iron ions to a solution containing NCC@Fe3O4@RB, they form complexes by binding with the weak-field ligands (such as nitrogen and oxygen) present within the structure of NCC@Fe3O4@RB. This interaction involves a high-spin coordination process, leading to the self-assembly of Fe3+ ions on the surface of NCC@Fe3O4@RB. The magnetization saturation (Ms) for NCC@Fe3O4, NCC@Fe3O4@NH2, and NCC@Fe3O4@RB was measured 44.7, 43.1, and 40.5 emu/g, respectively. As a result, single electrons are generated, which leads to increased paramagnetism, ultimately quenching the fluorescence. This fluorescence quenching effect caused by Fe3+ ions make the NCC@Fe3O4@RB fluorescent probe an efficient detector of Fe3+ ions in water. The main benefit of this fluorescence quenching mechanism lies in its ability to specifically target Fe3+ ions, without being influenced by the presence of other metal ions. This specificity guarantees that fluorescent probes utilizing magnetic fluorescence nanoparticles are highly efficient in detecting iron ions in water-based solutions, making them a valuable tool for environmental and biological purposes.

High Spin‐State Modulation of Catalytic Centers by Weak Ligand Field for Promoting Sulfur Redox Reaction in Lithium‐Sulfur Batteries

AbstractThe spin state of transition‐metal compounds in lithium‐sulfur batteries (LSBs) significantly impacts the electronic properties and the kinetics of sulfur redox reactions (SRR). However, accurately designing the spin state remains challenging, which is crucial for understanding the structure‐performance relationship and developing high‐performance electrocatalysts. Herein, the CoF2, specifically the Co2+ with 3d7 electrons in a high‐spin state distribution (t2g5eg2), were tailored predictably for the first time through the weak coordination field effect of the F element. Both DFT calculations and experimental results confirm that the spin state of Co2+ transitions from low‐ to high‐spin configurations and strongly interacts with sulfur species through Co−S and Li−F bonds during the SRR process. This interaction weakens the S−S bond, promoting its facile cleavage from both ends while also facilitating the rapid and uniform nucleation of Li2S2/Li2S, thus resulting in LSBs with a capacity of 447.7 mAh g−1 at 10 C rates and stable cycling for 1000 cycles, with an acceptable practical capacity of 585 mAh g−1 at a high sulfur loading mass of 10 mg cm−2. This work achieves rational control of the active Co2+ d electron state through the field effect and enriches the application of spin control to accelerate SRR in LSBs.

Bridging Carbonyl and Carbyne Complexes of Weak-Field Iron: Electronic Structure and Iron-Carbon Bonding.

Carbon monoxide inhibited forms of nitrogenases have carbonyl (CO) and carbide (C4-) bridges, which are common in synthetic iron complexes with strong-field ligand environments but rare in iron sites with weak-field ligand environments analogous to the enzyme. Here, we explore the fundamental bonding description of bridging CO in high-spin iron systems. We describe the isolation of several diiron carbonyls and related species, and elucidate their electronic structures, magnetic coupling, and characteristic structural and vibrational parameters. These high-spin iron complexes exhibit equivalent π-backbonding abilities to low-spin iron complexes. Sequential reduction and silylation of a formally diiron(I) bridging CO complex ultimately gives a formally diiron(IV) bridging carbyne complex. Despite the large range of formal oxidation states across this series, X-ray absorption spectroscopy and density functional theory calculations indicate that the electron density at the iron sites does not change. Thus, the [Fe(μ-CO)]2 core undergoes redox changes at the bridging carbonyls rather than the metal centers, rendering the metal's formal oxidation state misleading. The ability of the Fe2C2 core to easily shift charge between the metals and the ligands has implications for nitrogenases, and for other multinuclear systems for redox catalysis.

High Spin-State Modulation of Catalytic Centers by Weak Ligand Field for Promoting Sulfur Redox Reaction in Lithium-Sulfur Batteries.

The spin state of transition-metal compounds in lithium-sulfur batteries (LSBs) significantly impacts the electronic properties and the kinetics of sulfur redox reactions (SRR). However, accurately designing the spin state remains challenging, which is crucial for understanding the structure-performance relationship and developing high-performance electrocatalysts. Herein, the CoF2, specifically the Co2+ with 3d7 electrons in a high-spin state distribution (t2g 5eg 2), were tailored predictably for the first time through the weak coordination field effect of the F element. Both DFT calculations and experimental results confirm that the spin state of Co2+ transitions from low- to high-spin configurations and strongly interacts with sulfur species through Co-S and Li-F bonds during the SRR process. This interaction weakens the S-S bond, promoting its facile cleavage from both ends while also facilitating the rapid and uniform nucleation of Li2S2/Li2S, thus resulting in LSBs with a capacity of 447.7 mAh g-1 at 10 C rates and stable cycling for 1000 cycles, with an acceptable practical capacity of 585 mAh g-1 at a high sulfur loading mass of 10 mg cm-2. This work achieves rational control of the active Co2+ d electron state through the field effect and enriches the application of spin control to accelerate SRR in LSBs.

Controlling Reactivity through Spin Manipulation: Steric Bulkiness of Peroxocobalt(III) Complexes.

The intrinsic relationship between spin states and reactivity in peroxocobalt(III) complexes was investigated, specifically focusing on the influence of steric modulation on supporting ligands. Together with the previously reported [CoIII(TBDAP)(O2)]+ (2Tb), which exhibits spin crossover characteristics, two peroxocobalt(III) complexes, [CoIII(MDAP)(O2)]+ (2Me) and [CoIII(ADDAP)(O2)]+ (2Ad), bearing pyridinophane ligands with distinct N-substituents such as methyl and adamantyl groups, were synthesized and characterized. By manipulating the steric bulkiness of the N-substituents, control of spin states in peroxocobalt(III) complexes was demonstrated through various physicochemical analyses. Notably, 2Ad oxidized the nitriles to generate hydroximatocobalt(III) complexes, while 2Me displayed an inability for such oxidation reactions. Furthermore, both 2Ad and 2Tb exhibited similarities in spectroscopic and geometric features, demonstrating spin crossover behavior between S = 0 and S = 1. The steric bulkiness of the adamantyl and tert-butyl group on the axial amines was attributed to inducing a weak ligand field on the cobalt(III) center. Thus, 2Ad and 2Tb are an S = 1 state under the reaction conditions. In contrast, the less bulky methyl group on the amines of 2Me resulted in an S = 0 state. The redox potential of the peroxocobalt(III) complexes was also influenced by the ligand field arising from the steric bulkiness of the N-substituents in the order of 2Me (-0.01 V) < 2Tb (0.29 V) = 2Ad (0.29 V). Theoretical calculations using DFT supported the experimental observations, providing insights into the electronic structure and emphasizing the importance of the spin state of peroxocobalt(III) complexes in nitrile activation.

Relationship between Structure and Zero-Field Splitting of Octahedral Nickel(II) Complexes with a Low-Symmetric Tetradentate Ligand

Octahedral nickel(II) complexes are among the simplest systems that exhibit zero-field splitting by having two unpaired electrons. For the purpose of clarifying the relationship between structure and zero-field splitting in a low-symmetric system, distorted octahedral nickel(II) complexes were prepared with a tetradentate ligand, 2-[bis(2-methoxyethyl)aminomethyl]-4-nitrophenolate(1−) [(onp)−]. The complex [Ni(onp)(dmso)(H2O)][BPh4]·2dmso (1) (dmso = dimethyl sulfoxide) was characterized as a bulk sample by IR, elemental analysis, mass spectrometry, electronic spectra, and magnetic properties. The powder electronic spectral data were analyzed based on the angular overlap model to conclude that the spectra were typical of D4-symmetric octahedral coordination geometry with a weak axial ligand field. Simultaneous analysis of the temperature-dependent susceptibility and field-dependent magnetization data yielded the positive axial zero-field splitting parameter D (H = guβSuHu + D[Sz2 − S(S + 1)/3]), which was consistent with the weak axial ligand field. Single-crystal X-ray analysis revealed the crystal structures of [Ni(onp)(dmso)(H2O)][BPh4]·dmso (2) and [Ni(onp)(dmf)2][BPh4] (3) (dmf = N,N-dimethylformamide). The density functional theory (DFT) computations based on the crystal structures indicated the D4-symmetric octahedral coordination geometries with weak axial ligand fields. This study also showed the importance of considering g-anisotropy in magnetic analysis, even if g-anisotropy is small.

Synthesis, Characterization, and the Effect of Lewis Bases on the Nuclearity of Iron Alkoxide Complexes.

Inspired by the potential of alkoxides as weak-field ligands and their ability to bridge, we report herein a series of high-spin iron complexes supported by a bis-alkoxide framework PhDbf. A diiron complex [Fe2(PhDbf)2] (1a) is obtained upon metalation of the ligand, whereas addition of substituted pyridines affords five-coordinate mononuclear iron complexes [(R-Py)2Fe(PhDbf)] (2a-4a, R = H, p-tBu, p-CF3). The potential for nuclearity control of the metal complexes via auxiliary ligands is highlighted by the formation of asymmetric diiron species [(p-CF3-Py)Fe2(PhDbf)2] (5a) and [(m-CF3-Py)Fe2(PhDbf)2] (6a) with trifluoromethyl substituted pyridines, while electron-rich pyridines only produced monomeric species. Electronic properties analysis via UV-vis, electron paramagnetic resonance, 57Fe Mössbauer spectroscopy, and time-dependent density functional theory, along with redox capabilities of these complexes are reported to illustrate the effect of nuclearity on reactivity and the potential of these complexes to access higher oxidation states relevant in oxidative chemistry. Species 1a-5a, [(THF)2Fe(PhDbf)][PF6] (7), [PyFe(PhDbf)Cl] (2b), and [Py2Fe(PhDbf)][PF6] (2c) were characterized via SCXRD. Indirect evidence for the formation of dimeric Fe(III) species (1b, 5b, and 6b) is discussed.

Disproportionation of Co2+ in the Topochemically Reduced Oxide LaSrCoRuO5

AbstractComplex transition‐metal oxides exhibit a wide variety of chemical and physical properties which are a strong function the local electronic states of the transition‐metal centres, as determined by a combination of metal oxidation state and local coordination environment. Topochemical reduction of the double perovskite oxide, LaSrCoRuO6, using Zr, yields LaSrCoRuO5. This reduced phase contains an ordered array of apex‐linked square‐based pyramidal Ru3+O5, square‐planar Co1+O4 and octahedral Co3+O6 units, consistent with the coordination‐geometry driven disproportionation of Co2+. Coordination‐geometry driven disproportionation of d7 transition‐metal cations (e.g. Rh2+, Pd3+, Pt3+) is common in complex oxides containing 4d and 5d metals. However, the weak ligand field experienced by a 3d transition‐metal such as cobalt leads to the expectation that d7+ Co2+ should be stable to disproportionation in oxide environments, so the presence of Co1+O4 and Co3+O6 units in LaSrCoRuO5 is surprising. Low‐temperature measurements indicate LaSrCoRuO5 adopts a ferromagnetically ordered state below 120 K due to couplings between S=1/2 Ru3+ and S=1 Co1+.

Disproportionation of Co2+ in the Topochemically Reduced Oxide LaSrCoRuO5.

Complex transition-metal oxides exhibit a wide variety of chemical and physical properties which are a strong function the local electronic states of the transition-metal centres, as determined by a combination of metal oxidation state and local coordination environment. Topochemical reduction of the double perovskite oxide, LaSrCoRuO6 , using Zr, yields LaSrCoRuO5 . This reduced phase contains an ordered array of apex-linked square-based pyramidal Ru3+ O5 , square-planar Co1+ O4 and octahedral Co3+ O6 units, consistent with the coordination-geometry driven disproportionation of Co2+ . Coordination-geometry driven disproportionation of d7 transition-metal cations (e.g. Rh2+ , Pd3+ , Pt3+ ) is common in complex oxides containing 4d and 5d metals. However, the weak ligand field experienced by a 3d transition-metal such as cobalt leads to the expectation that d7+ Co2+ should be stable to disproportionation in oxide environments, so the presence of Co1+ O4 and Co3+ O6 units in LaSrCoRuO5 is surprising. Low-temperature measurements indicate LaSrCoRuO5 adopts a ferromagnetically ordered state below 120 K due to couplings between S=1 /2 Ru3+ and S=1 Co1+ .

Photoluminescence of Mn2+ in the Borosulfate Zn[B2(SO4)4]:Mn2+ - A Tool to Detect Weak Coordination Behavior of Ligands.

The impact of the surrounding ligand field is successfully exploited in the case of Eu2+ to tune the emission characteristics of inorganic photoactive materials with potential application in e.g., phosphor-converted white light-emitting diodes (pc-wLEDs). However, the photoluminescence of Mn2+ related to intraconfigurational 3d5-3d5 transitions is also strongly dependent on local ligand field effects and has been underestimated in this regard so far. In this work, we want to revive the idea how to electronically tune the emission color of a transition metal ion in inorganic hosts by unusual electronic effects in the metal-ligand bond. The concept is explicitly demonstrated for the weakly coordinating layer-like borosulfate ligand in the Mn(II)-containing solid solutions Zn1-xMnx[B2(SO4)4] (x = 0, 0.03, 0.04, 0.05, 0.10). Zn[B2(SO4)4]:Mn2+ shows orange narrow-band luminescence at 590 nm, which is an unusually short wavelength for octahedrally coordinated Mn2+ and indicates an uncommonly weak ligand field. On the other hand, the analysis of the interelectronic Racah repulsion parameters reveals ionic Mn-O bonds with values close to the Racah parameters of the free Mn2+ ion. Overall, this strategy demonstrates that electronic control of the metal-ligand bond can be a tool to make Mn2+ a potent alternative emitter to Eu2+ for inorganic phosphors.

Photolumineszenz von Mn2+ in dem Borosulfat Zn[B2(SO4)4] : Mn2+ – Eine Möglichkeit zum Nachweis schwach koordinierender Liganden

AbstractDer Einfluss des umgebenden Ligandenfelds wird im Fall von Eu2+ erfolgreich genutzt, um die Emission anorganischer photoaktiver Materialien durchzustimmen, die z. B. in phosphor‐konvertierten Weißlicht‐emittierenden Dioden (pc‐wLEDs) Anwendung finden. Allerdings ist auch die Photolumineszenz von Mn2+, die auf intrakonfiguralen 3d5–3d5‐Übergängen basiert, stark von lokalen Ligandenfeldeffekten abhängig. Dieser Aspekt wurde bislang eher vernachlässigt. In der vorliegenden Arbeit wollen wir daher die Idee wieder aufleben lassen, die Emissionsfarbe eines Übergangsmetall‐Ions in anorganischen Wirtsverbindungen durch ungewöhnliche elektronische Effekte in der Metall‐Ligand‐Bindung einzustellen. Das Konzept wird explizit für das schwach koordinierende, schichtartigen Borosulfat‐Anion in den Mn2+‐haltigen festen Lösungen Zn1‐xMnx[B2(SO4)4] (x=0; 0.03; 0.04; 0.05; 0.10) demonstriert. Zn[B2(SO4)4] : Mn2+ zeigt orange Schmalbandlumineszenz bei 590 nm, was eine ungewöhnlich kurze Wellenlänge für oktaedrisch koordiniertes Mn2+ darstellt und auf ein besonders schwaches Ligandenfeld hinweist. Eine Analyse der interelektronischen Racah‐Abstoßungsparameter deutet stark ionische Mn−O‐Bindungen mit Werten nahe der Racah‐Parameter des freien Mn2+‐Ions an. Insgesamt demonstriert diese Strategie, dass elektronische Anpassungen der Metall−Ligand‐Bindung als Instrument genutzt werden können, um Mn2+ zu einem potenten alternativen Emitter anstelle von Eu2+ für anorganische Leuchtstoffe zu machen.

Enhanced Understanding of Structure-Function Relationships for Oxomanganese(IV) Complexes.

A series of manganese(II) and oxomanganese(IV) complexes supported by neutral, pentadentate ligands with varied equatorial ligand-field strength (N3pyQ, N2py2I, and N4pyMe2) were synthesized and then characterized using structural and spectroscopic methods. On the basis of electronic absorption spectroscopy, the [MnIV(O)(N4pyMe2)]2+ complex has the weakest equatorial ligand field among a set of similar MnIV-oxo species. In contrast, [MnIV(O)(N2py2I)]2+ shows the strongest equatorial ligand-field strength for this same series. We examined the influence of these changes in electronic structure on the reactivity of the oxomanganese(IV) complexes using hydrocarbons and thioanisole as substrates. The [MnIV(O)(N3pyQ)]2+ complex, which contains one quinoline and three pyridine donors in the equatorial plane, ranks among the fastest MnIV-oxo complexes in C-H bond and thioanisole oxidation. While a weak equatorial ligand field has been associated with high reactivity, the [MnIV(O)(N4pyMe2)]2+ complex is only a modest oxidant. Buried volume plots suggest that steric factors dampen the reactivity of this complex. Trends in reactivity were examined using density functional theory (DFT)-computed bond dissociation free energies (BDFEs) of the MnIIIO-H and MnIV ═ O bonds. We observe an excellent correlation between MnIV═O BDFEs and rates of thioanisole oxidation, but more scatter is observed between hydrocarbon oxidation rates and the MnIIIO-H BDFEs.

SYNTHESIS AND CHARACTERISATION OF NI(II) COMPLEX OF L-LEUCINE

Synthesis of [NiL2 ].2H2O (L = L-leucine) was carried out in basic solution and the complex was analysed using gravimetric analysis, molar conductivity measurements, UV-Visible and IR spectroscopies. Molar conductivity measurements showed that the composition of the metal complex corresponds to a metal-amino acid ligand ratio of 1:2. The IR spectrum showed that L-leucine functions as bidentate ligand with coordination involving the carboxyl oxygen and the nitrogen of the amino group. The result also suggests the presence of water of crystallization in the complex. Electronic spectrum and magnetic susceptibility measurements suggested a four-coordinate local symmetry around Ni (tetrahedral) ions. The results also intimate that the ligand, L-leucine, is a weak field ligand as it formed high spin complex with Ni(II) ions. Metal content and hydration water analyses showed that the complex of Ni contains two moles of water of crystallization. The results also hinted that the Ni(II) complex has no aqua ligand in their inner coordination sphere.

The weak ligand field in lanthanoid(III) hydrogensulfate‐sulfates

AbstractThe hydrogensulfate‐sulfates Ln(HSO4)(SO4) (Ln: Sm, Eu, Gd, Tb, Dy) have been crystallized from sulfuric acid and their thermal decomposition behavior has been studied. The crystal structures for all members of the series were refined from X‐ray single‐crystal diffraction data (for all: Tb(HSO4)(SO4) structure type, P21, Z=2, a≈6.66 Å, b≈6.63 Å, c≈6.82 Å, β≈104.6°). Optical spectra (Sm–Dy) and magnetic susceptibilities (Eu–Dy) have been measured. For comparison the octahydrates Ln2(SO4)3 ⋅ 8 H2O (Sm, Eu) and the anhydrous sulfates Ln2(SO4)3 (Sm, Eu) have also been characterized by optical spectroscopy and magnetic measurements. Ligand field analyses (angular overlap model) based on these data suggest for the square‐antiprismatic [LnIIIO8] chromophores in the hydrogensulfate‐sulfates a rather weak ligand field, which is comparable only to that in ultraphosphates LnP5O14 and in contrast to the much stronger field observed for most other lanthanoid(III) oxo‐compounds studied so far.

Solvent Coligand-Induced Spin State Variation in Iron(II) Complexes Bearing Pentadentate N5 Ligand Toward the Construction of an N5O Spin Crossover Center

Three iron(II) complexes having a 1,2,3-triazole-containing linear pentadentate N5 ligand L3-Me-3Me and different monodentate solvent coligand X, [Fe(L3-Me-3Me)X](BPh4)2 [L3-Me-3Me = bis(N,N′-1-methyl-1H-1,2,3-triazol-4-yl-methylideneaminopropyl)methylamine; X = MeCN (1), dimethylformamide (DMF) (2), and dimethyl sulfoxide (DMSO) (3)] have been selectively prepared by the choice of reaction solvent. Along the well-known spectrochemical series, the strong-field solvent ligand MeCN generates a low-spin (LS) complex 1, the weak-field ligand DMSO generates a high-spin (HS) complex 3, and the complex 2 coordinated by the medium-field ligand DMF exhibits gradual and reversible one-step HS↔LS spin crossover (SCO) with T1/2 = 173 K in the temperature range of 400–5 K. This spin state variation among LS 1, HS 3, and SCO 2 has been investigated by the combination of temperature-dependent magnetic susceptibilities measurements, single-crystal X-ray diffraction (SCXRD) studies, Hirshfeld surface analyses, and density functional theory calculations. In addition, the details of structural change between HS and LS states of an N5O iron(II) center upon SCO are revealed for the first time by the variable-temperature SCXRD studies for 2 at nine different temperatures in which the difference of Fe–O bond length between the two spin states is shorter than that of any other Fe–N bond lengths.

UV/blue/green converted efficient red-NIR photoluminescence in Cr incorporated MgAl2O4 nanocrystals: Site selective emission tailored through cation inversion and intrinsic defects

The UV/visible activated near-infrared (NIR) phosphors have many applications in solid state lighting, night vision devices and bio-imaging. The early research reported the red-NIR emitting phosphors doped with Cr3+ centers upon visible light excitation. Here, in this work the intense red-NIR emission and color tuning is achieved for broad excitation range (UV/blue/green) through Cr dopant induced defect centers and cation inversion in MgCr Al2O4 ( = 0.5, 1, 3, 5 and 10 mol%) nanocrystals. The Cr3+ doped MgAl2O4 nanocrystals were synthesized by combustion method through stoichiometric substitution of Mg by Cr, while most of the Cr3+ ions occupied the octahedral sites of spinel host with the formation of antisite defects, Cr3+ clusters, magnesium and oxygen vacancies. These defect centers were probed through Rietveld refinement, photoluminescence (PL), x-ray photoelectron and nuclear magnetic resonance spectra analyses. At UV excitation, the intrinsic defects played an interesting role in exhibiting the blue-violet emission attributed to host lattice defects and red-NIR emission attributed to strong/weak ligand field octahedral Cr3+ sites, via charge transfer to Cr3+ ions. The PL spectra evinced the enhanced red-NIR emission intensity upon 266 nm excitation than upon blue and green light excitation. Further, the weak ligand field site emission is found to be dominating with increase in doping concentration. Thus, Cr doped MgAl2O4 nanocrystals showed their potency of exhibiting the intense red-NIR emission and color tuning (from red purple to bluish purple and then to red color) upon UV/blue/green excitation.

Ferric Pyrophosphate Forms Soluble Iron Coordination Complexes with Zinc Compounds and Solubilizing Agents in Extruded Rice and Predicts Increased Iron Solubility and Bioavailability in Young Women

BackgroundCo-extrusion of ferric pyrophosphate (FePP) with solubilizers, citric acid/trisodium citrate (CA/TSC), or ethylenediaminetetraacetic acid (EDTA) sharply increases iron absorption. Whether this can protect against the inhibition of iron absorption by phytic acid (PA) is unclear. Sodium pyrophosphate (NaPP) may be a new enhancer of iron absorption from FePP. ObjectivesOur objectives were to 1) investigate the ligand coordination of iron, zinc, and solubilizers in extruded rice and test associations with iron solubility and absorption, 2) assess whether co-extrusion of FePP + CA/TSC rice can protect against inhibition of iron absorption by PA; 3) determine the effect of zinc oxide (ZnO) compared with zinc sulfate (ZnSO4), and 4) quantify iron absorption from FePP + NaPP rice. MethodsWe produced labeled 57FePP rice cofortified with ZnSO4 and EDTA, CA/TSC or NaPP, and FePP + EDTA rice with ZnO. We used electron paramagnetic resonance (EPR) to characterize iron-ligand complexes. We measured in vitro iron solubility and fractional iron absorption (FIA) in young women (n = 21, age: 22 ± 2 y, BMI: 21.3 ± 1.5 kg/m2 geometric mean plasma ferritin, 28.5 μg/L) compared with ferrous sulfate (58FeSO4). FIA was compared by linear mixed-effect model analysis. ResultsThe addition of zinc and solubilizers created new iron coordination complexes of Fe(III) species with a weak ligand field at a high-spin state that correlated with solubility (r2 = 0.50, P = 0.02) and absorption (r2 = 0.72, P = 0.02). Phytic acid reduced FIA from FePP + CA/TSC rice by 50% (P < 0.001), to the same extent as FeSO4. FIA from FePP + EDTA + ZnO and FePP + EDTA + ZnSO4 rice did not significantly differ. Mean FIAs from FePP + EDTA + ZnSO4, FePP + CA/TSC + ZnSO4, and FePP + NaPP + ZnSO4 rice were 9% to 11% and did not significantly differ from each other or from FeSO4. ConclusionRice extrusion of FePP with solubilizers resulted in bioavailable iron coordination complexes. In the case of FePP + CA/TSC, PA exerted similar inhibition of FIA as with FeSO4. FePP + NaPP could be a further viable solubilizing agent for rice fortification.This study was registered at clinicaltrials.gov as NCT03703739.

Stability and bonding of carbon(0)-iron-N2 complexes relevant to nitrogenase co-factor: EDA-NOCV analyses.

The factors/structural features which are responsible for the binding, activation and reduction of N2 to NH3 by FeMoco of nitrogenase have not been completely understood well. Several relevant model complexes by Holland et al. and Peters et al. have been synthesized, characterized and studied by theoretical calculations. For a matter of fact, those complexes are much different than real active N2 -binding Fe-sites of FeMoco, which possesses a central C(4-) ion having an eight valence electrons as an μ6 -bridge. Here, a series of [(S3 C(0))Fe(II/I/0)-N2 ]n- complexes in different charged/spin states containing a coordinated σ- and π-donor C(0)-atom which possesses eight outer shell electrons [carbone, (Ph3 P)2 C(0); Ph3 P→C(0)←PPh3 ] and three S-donor sites (i.e. - S-Ar), have been studied by DFT, QTAIM, and EDA-NOCV calculations. The effect of the weak field ligand on Fe-centres and the subsequent N2 -binding has been studied by EDA-NOCV analysis. The role of the oxidation state of Fe and N2 -binding in different charged and spin states of the complex have been investigated by EDA-NOCV analyses. The intrinsic interaction energies of the Fe-N2 bond are in the range from -42/-35 to -67 kcal/mol in their corresponding ground states. The S3 C(0) donor set is argued here to be closer to the actual coordination environment of one of the six Fe-centres of nitrogenase. In comparison, the captivating model complexes reported by Holland et al. and Peter et al. possess a stronger π-acceptor C-ring (S2 Cring donor, π-C donor) and stronger donor set like CP3 (σ-C donor) ligands, respectively.

Heteroleptic Co(III) bisdithiocarbamato-dithione complexes: Synthesis, structure and bonding of [Co(Et2dtc)2(R2pipdt)]BF4 (R = Me, 1; Ph, 2; pipdt = piperazin-2,3-dithione) complexes

The reaction between the binuclear cobalt complex, [Co2(Et2dtc)5]+, and Me2pipdt and Ph2pipdt ligands has provided almost quantitatively the cobalt tris-chelate heteroleptic complexes [Co(Et2dtc)2(R2pipdt)]BF4 (1 and 2). The molecular structure of 2 shows the metal in a distorted octahedral geometry. The nature of the bonding in these complexes has been elucidated with the support of DFT TD-DFT calculations. Both chelating S,S donors work as weak-field ligands. The comparison of the chemical reactivity for the homoleptic dithiocarbamate complex [Co(Et2dtc)3] and the heteroleptic [Co(Et2dtc)2(Ph2pipdt)]+ derivative shows that the global softness σ is significantly higher in [Co(Et2dtc)2(Ph2pipdt)]+ than in the homoleptic dithiocarbamate complex, due to a reduction of nephelauxetic effect induced by the dithioxamide ligand. The kinetics for the reaction between the reagents in CH2Cl2 has been followed spectrophotometrically as a function of temperature in pseudo-first order conditions with respect to R2pipdt ligands. Kinetic results further support a reaction mechanism involving a one-end reversible dissociation of the [Co2(Et2dtc)5]+ dimer forming a reactive cobalt(III)dithiocarbamato center susceptible to attack by nucleophiles. The effectiveness and versatility of the above reaction is an easy and clean method to provide heteroleptic-dithiocarbamates with a variety of suitable ligands of interest for applicative purposes.