Oxygen Lone Pair Research Articles

Water Adsorption on the β-Dicalcium Silicate Surface from DFT Simulations

β-dicalcium silicate (β-Ca2SiO4 or β-C2S in cement chemistry notation) is one of the most important minerals in cement. An improvement of its hydration rate would be the key point for developing environmentally-friendly cements with lower energy consumption and CO2 emissions. However, there is a lack of fundamental understanding on the water/β-C2S surface interactions. In this work, we aim to evaluate the water adsorption on three β-C2S surfaces at the atomic scale using density functional theory (DFT) calculations. Our results indicate that thermodynamically favorable water adsorption takes place in several surface sites with a broad range of adsorption energies (−0.78 to −1.48 eV) depending on the particular mineral surface and adsorption site. To clarify the key factor governing the adsorption of the electronic properties of water at the surface were analyzed. The partial density of states (DOS), charge analysis, and electron density difference analyses suggest a dual interaction of water with a β-C2S (100) surface including a nucleophilic interaction of the water oxygen lone pair with surface calcium atoms and an electrophilic interaction (hydrogen bond) of one water hydrogen with surface oxygen atoms. Despite the elucidation of the adsorption mechanism, no correlation was found between the electronic structure and the adsorption energies.

Existence of a Preferred Orientation for the Methoxy Group on an Extended Aromatic System.

AbstractThe conformations of a methoxy group introduced on naphthalene in position 2 has been investigated both experimentally (searches in crystallographic data, NOE measurements by NMR) and theoretically with ab initio calculations. While expected at first glance as being equivalent and predicted as such by force field methods, the two conformations where the methoxy is in the plane of the aromatic ring and turned either towards one or the other proton of naphthalene are actually very different in energy : ΔE=1.2 to 1.8 kcal mol−1, a surprisingly high value! The delocalization of the oxygen lone pair on the π‐system of the aromatic ring differs between the two conformers and is proposed to account predominantly for such unexpectedly large ΔE. It is our opinion that given the magnitude of the energies involved, force field methods should be corrected to take into account this conformational effect.

Experimental and computational VUV photoabsorption study of dimethyl carbonate: A green solvent

VUV photoabsorption spectrum of dimethyl carbonate in the energy region 7–11 eV and its complete spectral analysis with the aid of quantum chemical calculations is reported for the first time. The spectrum recorded using synchrotron radiation comprises of weak bands overlapping a broad intense continuum. With a view to interpret possible vibronic structure, gas phase infrared spectrum in the region 500–4000 cm−1 is revisited. Density functional theory (DFT) and time dependent DFT (TDDFT) methodologies are used to obtain ground state geometry, vibrational frequencies and vertical excitation energies of dimethyl carbonate. The intense broad features in the spectrum could be attributed to valence transitions. Based on quantum defect calculations, energy ordering and symmetry, weak bands are designated as ns, np and nd type Rydberg transitions converging to the first five ionization potentials. The highest occupied molecular orbital is nonbonding in nature and largely localized on the oxygen atom of carbonyl group and quantum defect values obtained are consistent with excitation from oxygen lone pair. Excellent correlation is obtained between theoretically predicted (CAM-B3LYP levels of theory) and experimentally observed excited state energies. Potential energy curves of ground and first few excited states generated with a view to provide additional insights into their nature and further describe the observed spectra. The present study provides a comprehensive experimental and computation analysis of the VUV photoabsorption spectroscopy of dimethyl carbonate.

Intermolecular Carbonyl···Carbonyl Interactions in Transition-Metal Complexes.

We performed a comprehensive analysis of intermolecular carbonyl-carbonyl interactions in transition-metal complexes. Those interactions can be classified in two main types depending on the organometallic or organic nature of the donor carbonyl: M-CO···CO and R-CO···CO, respectively. By means of a combined structural and computational study we unraveled their geometrical features and strength. Moreover, electronic structure, natural bond orbitals, energy decomposition analysis, and quantum theory of atoms in molecules calculations were performed to try to understand their nature. Remarkably, we discovered that these carbonyl-carbonyl contacts have several features of the n → π* interaction. The charge transfer from an oxygen lone pair to an empty antibonding π orbital of the acceptor carbonyl is also accompanied by an electrostatic Oδ-···Cδ+ interaction. To the best of our knowledge this is the first report of an intermolecular n → π* interaction in metal complexes. These results might be significant, for instance, for the catalytic activation of carbonyl-containing small molecules with metal compounds or in the design of hybrid organic-inorganic materials, metal-organic frameworks, and other extended structures.

Spectroscopy of diethyl carbonate, a green solvent: An experimental and theoretical study

The electronic spectra of diethyl carbonate (DEC) based on photoabsorption spectroscopy using synchrotron radiation are investigated in the 6.8-11.5 eV region. The VUV photo absorption spectrum reported here for the first time comprises broad features in the 7-11 eV region with few weak overriding spectral peaks. The broad peaks could be assigned to valence excitations, while the weak ones correspond to the Rydberg series of ns, np, and nd types, thus converging to the first five ionization potentials. Quantum defect values obtained are consistent with the excitation of an electron from oxygen lone pair. Infrared bands of DEC were revisited in the 600-3100 cm−1 region. The observed infrared bands of DEC could be assigned by DFT calculations. The TDDFT methodology is used to compute the vertical excited state energies, valence/Rydberg nature, and oscillator strengths of the excited electronic states. A good agreement using the CAM-B3LYP level of theory is achieved between the theoretically predicted values and experimental observations. In the ionic limit of DEC, the lengthening of the CO and CO–C2H5 bond lengths is predicted. The potential energy curves of the first few excited states assisted in additional insights on the nature of the excited states and their role in photo dissociation dynamics. This study gives a first comprehensive report on the analysis of absorption spectra of DEC in the VUV region and the complete spectral assignments in the VUV and IR regions by quantum chemical calculations.

Natural Bond Orbital Analysis of [Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>2+/3+</sup> and [Zn(H<sub>2</sub>O)<sub>6</sub>](H<sub>2</sub>O)<sub>N</sub><sup>2+</sup>;N=0-4

Nature of delocalization of the electrons from the ligands to metals in the first coordination sphere of the high-spin complexes [Fe(H2O)6]2+/3+ and [Zn(H2O)6]2+ are computationally studied using density functional theory. Among the studied complexes, natural charge transfer from H2O ligands to metal ion is found to be maximum of 1.556e in [Fe(H2O)6]3+ and minimum of 0.621e in [Zn(H\2O)6]2+. On the other hand, the interaction between the lone pairs of oxygen with metal ion was found to be stronger in [Zn(H2O)6]2+ than in the complexes with second coordination sphere. Number of such strong interactions in the first coordination sphere was found to be decreased with the addition of H2O ligands in the second coordination sphere.Journal of Institute of Science and Technology Volume 22, Issue 2, January 2018, Page: 148-155

Syn vs Anti Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis.

A comparative study of syn vs anti carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the anti form, all three bond angles surrounding Ccarboxyl of the -COOH group are close to ∼120°, as expected for a C-sp2 atom, whereas in the syn form, the ∠Cα-C(O)-Ohydroxyl angle is significantly smaller by 5-10°. The oxygen atom in the carboxyl group is more electronegative in the anti form, so the polarity of the acidic O-H bond is higher in the anti form compared to the syn form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated anti carboxylic acid forms the strongest O-H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp2 and sp3 lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds.

One-pot synthesis, quantum chemical calculations and X-ray diffraction studies of thiazolyl-coumarin hybrid compounds

Two closely related hybrid species containing both, thiazolyl and coumarin groups, were synthesized by using two different one-pot procedures from a common precursor. The reaction of α-bromoacetylcoumarin with thioacetamide in methanol furnished 3‑(2‑methylthiazol‑4‑yl)‑2H‑chromen‑2‑one (2), whereas refluxing α‑bromoacetylcoumarin with potassium thiocyanate in ethanol afforded 3‑(2‑ethoxythiazol‑4‑yl)‑2H‑chromen‑2‑one (3). Both derivatives were fully characterized by spectroscopic methods, elemental analysis and X-ray diffraction studies. Intramolecular C4H⋯N and C5′H⋯OC hydrogen bonds between the heterocycles determine the conformational behavior. The co-planarity of the coumarin and thiazolyl rings favors the occurrence of two remote orbital interactions involving the oxygen and nitrogen lone pairs and the corresponding σ*CH electron acceptor, as demonstrated by Natural Bond Orbital population analysis. The 2-substitution of the thiazol‑4‑yl group has little effect on the molecular structures but causes significant differences in the crystal packing of the two compounds.

The effect of Pineapple Leaf Fiber (PALF) incorporation into Polyethylene Terephthalate (PET) on FTIR, morphology and wetting properties

Pineapple Leaf Fibers (PALF) which is rich in cellulose, relatively inexpensive and abundantly available has the potential for polymer reinforcement. In this study, Polyethylene Terephthalatate (PET) was added with PALF and electro-spinned. The resulting mats were compared with PET neat electrospun. The samples later were examined by Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) and contact angle (CA). Briefly, SEM results indicated that the present of fibers led to a tendency of lower average fiber diameter compared to the PET neat. Two distinct fiber networks with intersecting fibers were observed in PALF/PET. One networks probably corresponds to PET and the others to PALF. FTIR analysis shows the intensity peak represent carbonyl at ∼3400cm-1 and ester at ∼1100 cm-1 decreased. It is suggested interaction occurred between lone pair of oxygen in the group with hydrogen group in PALF. New peak were observed at 3400 cm-1 in PALF/PET that indicated present of hydrogen bonding as well as its hydrophilic tendancy. The contact angle of PET signify high average value 1560 that comes with hydrophobic properties compared to PALF/PET with average value 160 with more hydrophilic properties.

CO2 interaction with violarite (FeNi2S4) surfaces: a dispersion-corrected DFT study.

The unbridled emissions of gases derived from the use of fossil fuels have led to an excessive concentration of carbon dioxide (CO2) in the atmosphere with concomitant problems to the environment. It is therefore imperative that new cost-effective catalysts are developed to mitigate the resulting harmful effects through the activation and conversion of CO2 molecules. In this paper, we have used calculations based on the density functional theory (DFT), including two semi-empirical approaches for the long-range dispersion interactions (-D2 and -D3), to explore the interaction of CO2 with the surfaces of spinel-structured violarite (FeNi2S4). This ternary sulfide contains iron ions in the highest possible oxidation state, while the nickel atoms are in the mixed 2+/3+ valence state. We found that CO2 interaction with violarite is only moderate due to the repulsion between the oxygen lone pairs and the electronic clouds of the sulfur surface atoms. This suggests that the CO2 activation is not dictated by the presence of nickel, as compared to the pure iron-isomorph greigite (Fe3S4). These results differ from findings in (Ni,Fe) ferredoxin enzymes, where the Ni/Fe ratio influences the redox potential, which suggests that the periodic crystal structure of violarite may hinder its redox capability.

Mechanistic insights into the photogeneration and quenching of guanine radical cation via one-electron oxidation of G-quadruplex DNA.

Herein, mechanistic aspects of the photogeneration and quenching of guanine radical cation through one-electron oxidation of the G-quadruplex of G2T2G2TGTG2T2G2 (TBA) sequence were investigated by a combined quantum mechanical/molecular mechanical (QM/MM) approach at the CASPT2//CASSCF/AMBER level of theory. Herein, one electron promotion of the oxygen lone pair of the photo-excited photosensitizer peroxydisulfate to its O-O σ* orbital was first demonstrated to become tunable through the varied reduction ability of the G base in the presence or absence of interbase hydrogen bonding, thereby dynamically controlling the deprotonation site in G-quadruplex TBA. The quenching of G radical cation mediated by the formation of SO42-via photoinduced electron transfer can be triggered effectively by the deprotonation reaction of free proton rather than that of the hydrogen-bonded proton in G-G (G-quartet) and G-T (loop) aqueous surrounding. By calculating the deprotonation paths for the G radical cation, the deprotonation reactions in G-quadruplex TBA were verified to proceed predominantly along the site of imino proton (N1-H) in the loop moiety; this showed the coexisting occurrence of amino (N2-H) deprotonation in the G-quartet part. The mechanistic features discussed in this study represent significant advances in the understanding of DNA radical chemistry.

Solvation of Amides in DMSO and CDCl3: An Attempt at Quantitative DFT-Based Interpretation of 1H and 13C NMR Chemical Shifts.

The study concerns N-methyl-2-pyrrolidinone, N,N-dimethylformamide, 2-pyrrolidinone, N-methylformamide, and formamide in DMSO-d6 and CDCl3 solutions. It has been shown that the results of DFT calculations [B3LYP and/or PBE0 6-311++G(2d,p), PCM] of molecular geometries and magnetic shielding are able to reproduce very well the amide 1H NMR and 13C NMR chemical shifts measured in these solvents provided that the specific solvation of the solute molecules and their association are taken into account and also that comparison of the experimental and theoretical data is carefully done. Analysis of the chemical shift data points out that in CDCl3 solutions primary and secondary amides are partially associated and that their carbonyl oxygen lone electron pairs are specifically solvated by solvent molecules. At the same time, association of the amides seems to be of minor importance in DMSO, while their N-H hydrogens form strong hydrogen bonds with solvent molecules.

Conformational Preferences of the Phenyl Group in 1-Phenyl-1-X-1-silacyclo-hexanes (X = MeO, HO) and 3-Phenyl-3-X-3-silatetrahydropyrans (X = HO, H) by Low Temperature 13C NMR Spectroscopy and Theoretical Calculations.

New Si-phenyl-substituted silacyclohexanes and 3-silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosix-membered ring by low temperature 13C NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Phax ⇆ Pheq equilibrium constants at 103 K are 2.21 for 1 and 4.59 for 4. In complete agreement with former studies of similar silicon compounds, molecules 1 and 4 prefer to adopt the Pheq conformation. The conformational equilibria of 1-hydroxy-1-phenylsilacyclohexane 2 and 3-hydroxy-3-phenyl-3-silatetrahydropyran 3 could not be frozen at 100 K and proved to be heavily one-sided (if not anancomeric). Obviously, there is a general trend of predominance of Phax conformer in the gas phase and of Pheq in solution. For the isolated molecules of silanols 2 and 3, calculations allowed to explain the axial predominance of the phenyl group by a larger polarization of the Si-Ph than of the Si-O bond in the Phax conformer and additional destabilization of 3-Pheq conformer by repulsion of unidirectional dipoles of the endocyclic oxygen lone pair and of the highly polar axial Si-O bond.

Twisted intramolecular charge transfer investigation of semi organic l-Glutamic acid hydrochloride single crystal for organic light-emitting and optical limiting applications

Single crystals of l-Glutamic acid hydrochloride (LGHCl) were grown by slow evaporation solution technique and good crystalline perfection was confirmed by Powder X-ray diffraction studies. The complete vibrational studies of the compound were analyzed by FT-IR, FT-Raman and UV–visible spectra combined with Normal Coordinate Analysis (NCA) following the scaled quantum mechanical force field methodology and density functional theory (DFT). Twisted Intramolecular Charge Transfer (ICT) occurs due to the presence of strong ionic intra-molecular NH⋯O hydrogen bonding was confirmed by Hirshfeld Surface analysis. The existence of intermolecular NH⋯Cl hydrogen bonds due to the interaction between the lone pair of oxygen with the antibonding orbital was established by NBO analysis. The Z-scan result indicated that the title molecule exhibits saturable absorption behavior. The attractive third-order nonlinear properties suggest that LGHCl can be a promising candidate for the design and development devices for optical limiting applications. LGHCL exhibits distinct emission in the blue region of the fluorescence lifetime which proves to be a potential candidate for blue- Organic light-emitting diodes (OLEDs) fabrication.

Dispersive Optical Activity of (R)-Methylene Norbornene: Intrinsic Response and Solvation Effects.

The dispersive optical activity of a homoconjugated bicyclic diene, (R)-methylene norbornene (R-MNB), was interrogated under complementary vapor-phase and solution-phase conditions to elucidate the structural/electronic provenance of its unusual chiroptical signatures and to explore the marked influence of environmental perturbations. The intrinsic (isolated-molecule) values of specific rotation measured at 355 and 633 nm (1623.5 ± 5.5 and 390.4 ± 3.7 deg dm-1 (g/mL)-1) were found to be factors of 3.9 and 2.1 smaller in magnitude than analogous quantities obtained for the kindred enone, (R)-norbornenone (R-NBO), reflecting, in part, the loss of prominent magnetic-dipole contributions from the C═O moiety and the exclusion of electron delocalization from the oxygen lone pairs. The wavelength-resolved rotatory powers of R-MNB were enhanced dramatically (by ∼40% on average) upon dissolution in any of the four common solvents targeted by the present study (acetonitrile, di-n-butylether, cyclohexane, and chloroform), yet displayed only a slight dependence on the exact nature of the surrounding liquid (±2.7% variation from the mean at 589.3 nm). Quantum-chemical calculations built upon the linear-response frameworks of density-functional theory and coupled-cluster theory were enlisted to interpret experimental results, with the substantial effects incurred by nonspecific solvation phenomena being explored through use of polarizable continuum models and bulk property-response relationships. Aside from enumerating the varied quality of agreement attained between computational predictions and polarimetric measurements, these efforts have found that refractive-index correlations, akin to those embodied in the venerable (albeit often discounted) Lorentz local-field correction, afford a viable means of linking the chiroptical behavior of R-MNB across phases.

The molecular structure of 5-X-isatines where (X = F, Cl, and Br) determined by gas-phase electron diffraction with theoretical calculations

The molecular structures of 5-X-isatines where X = F (1), Cl (2), and Br (3) were studied by gas-phase electron diffraction (GED) and theoretical calculations at M062X/aug-cc-pVTZ and MP2/aug-cc-pVTZ levels. The best fit of the experimental scattering intensities was obtained for a molecular model of Cs symmetry. The small differences between similar geometric parameters were constrained at the values calculated at the M062X level. The bond distances in the benzene ring are in agreement with their standard values. The (O)CC(O) carbon-carbon bonds of the pyrrole moiety in title compounds (1.581(11), 1.578(8), 1.574(12) Å, respectively) are remarkably lengthened in comparison with standard C(sp2)–C(sp2) value, 1.425(11) Å for N-methylpyrrole. According to NBO analysis this lengthening cannot be attributed to the electrostatic repulsion of oxygen lone pairs alone and is, mainly, due to the hyperconjugation, that is delocalization of oxygen lone pairs of π-type into the corresponding carbon-carbon antibonding orbital, nπ(O)→σ*(CC). Deletion of σ*(CC) orbital followed by subsequent geometry optimization led to shortening of the corresponding CC bond by 0.05–0.06 Å. Electronegative halogen atoms led to increase of CCXC endocyclic bond angles at ipso carbon atom as compared with the value of 120° in regular hexagon. According to different aromaticity descriptors, aromaticity of benzene moiety of title compounds is smaller in comparison with benzene molecule. External magnetic field induces diatropic ring current in benzene moiety. Local reactivity descriptors that indicate sites in a molecule that are susceptible to nucleophilic, electrophilic and radical attack are calculated.

Study of the modes of adsorption and electronic structure of hydrogen peroxide and ethanol over TiO2 rutile (110) surface within the context of water splitting

While photocatalytic water splitting over many materials is favourable thermodynamically the kinetic of the reaction is very slow. One of the proposed reasons linked to the slow oxidation reaction rate is H2O2 formation as a reaction intermediate. Using Density Functional Theory (DFT) H2O2 is investigated on TiO2 rutile (110) surface to determine its most stable adsorption modes: molecular, (H)O(H)O − (a), partially dissociated, (H)OO − (a), and fully dissociated (a) − OO − (a). We then compare H2O2 interaction to that of a fast hole scavenger molecule, ethanol. Geometry, electronic structure, charge density difference and work function determination of both adsorbates are presented and compared using DFT with different functionals (PBE, PBE-D, PBE-U, and HSE + D). H2O2 is found to be strongly adsorbed on TiO2 rutile (110) surface with adsorption energies reaching 0.95 eV, comparable to that of ethanol (0.89 eV); using GGA PBE. The negative changes in the work function upon adsorption were found to be highest for molecular adsorption ( − 1.23 eV) and lowest for the fully dissociated mode ( − 0.54 eV) of H2O2. This may indicate that electrons flow from the surface to the adsorbate in order to make O(s)-H partially offset the overall magnitude of the oxygen lone pair interaction (of H2O2) with Ti4+ cations. Examination of the electronic structure through density of states (DOS) at the PBE level of computation, indicates that the H2O2 highest occupied molecular orbital (HOMO) level is not overlapping with oxygen atoms of TiO2 surface at any of its adsorption modes and at any of the computation methods. Some overlap is seen using the HSE + D computational method. On the other hand the dissociated mode of ethanol (ethoxides) does overlap with all computational methods used. The high adsorption energy and the absence of overlapping of the HOMO level of H2O2 with TiO2 rutile (110) surface may explain why water splitting is slow.

ВЛИЯНИЕ РАЗЛИЧНОГО ВИДА ОБРАБОТОК НА ОПТИЧЕСКИЕ СВОЙСТВА МЫШЕЧНОЙ ТКАНИ ЖИВОТНОГО ПРОИСХОЖДЕНИЯ

A comparative study of the effect of successive aqueous, salt and alkaline extractions on the spectral characteristics of the surface of ground pork muscle tissue and its main components was per-formed using attenuated total reflectance IR spectroscopy (ATR - IR) and electron spectroscopy of diffuse reflectance (ESDR). It is shown that, unlike IR spectroscopy, which is a method of group analysis of functional groups, the ESDR method makes it possible to test the component composition of complex biomaterials - proteins, lipids, carbohydrates. The high resolution, sensitivity and informativity of the method are determined by the discrete-ness of electron excitation energies of oxygen lone pairs present in carbonyl groups. These carbonyl groups are found in almost all materials of biologic tissue components, although belonging to their different types - sarcoplasm, muscle fibre as well as stroma and its proteins.

Ligand Design toward Multifunctional Substrate Reductive Transformations.

The synthesis of bis(N1-phenyl-5-hydroxypyrazol-3-yl)pyridines ("L") is described, and these are silylated to achieve analogues ("Si2L") without the variable of the hydroxyl proton mobility. One hydroxyl example is characterized in its bis-pincer iron(II) complex, which shows every OH proton involved in hydrogen bonding. The steric bulk of the silylated N-phenyl-substituted ligands allows the synthesis and characterization of paramagnetic (Si2L)FeCl2 complexes, and one of these is reduced, under CO, to give the diamagnetic (Si2L)Fe(CO)2 species. Structural comparison and density functional theory calculations of the dichloride and dicarbonyl species show that much, but not all, of the reduction occurs at both the ligand pyridine and pyrazole rings, and thus this ligand type is more resistant to reduction than the simpler bis(iminopyridines). The OSiR3 substituent offers a useful diagnostic of reduction at pyrazole via the degree of π-donation to pyrazole by the oxygen lone pairs, and the stereoelectronic features of the NPh moiety are analyzed. The X-ray photoelectron spectroscopy binding energies of both iron and nitrogen are analyzed to show details of the locus of reduction.

The Li3RuyNb1–yO4 (0 ≤ y ≤ 1) System: Structural Diversity and Li Insertion and Extraction Capabilities

Searching for novel high-capacity electrode materials combining cationic and anionic redox processes is an ever-growing activity within the field of Li-ion batteries. In this respect, we report on the exploration of the Li3RuyNb1–yO4 (0 ≤ y ≤ 1) system with an O/M ratio of 4 to maximize the number of oxygen lone pairs, responsible for the anionic redox. We show that this system presents a very rich crystal chemistry with the existence of four structural types, which derive from the rocksalt structure but differ in their cationic arrangement, creating either zigzag, helical, jagged chains or clusters. From an electrochemical standpoint, these compounds are active on reduction via a classical cationic insertion process. The oxidation process is more complex, because of the instability of the delithiated phase. Our results promote the use of the rich Li3MO4 family as a viable platform for a better understanding of the relationships between structure and anionic redox activity.