Bond Covalency Research Articles

Synthesis, structural characterization, crystal structure and theoretical study of a Pd(II)-salen complex with propylene linkage

A Pd(II)-salen complex derived from salen ligand is reported. The reported complex is investigated by microanalyses (C, H, N), ESI-MS spectrometry, FT-IR, 1H and 13C NMR and UV/Vis spectroscopic studies. In addition, crystal structure measurement study has also been carried out in order to confirm the structure of Pd(II)-salen complex.In order to explore the insights into the structural bonding of the studied complex, computational measurements has been carried out. Combined topology and NBO studies were made to explore the nature of PdO and PdN bonding in the complex. The natural charges showed that the transfers of the negative charge from the ligand to palladium atom is at 1.4157–1.4312 e. Atom in a molecule (AIM) analysis showed the electron density (ρ(r) > 0.1) and its Laplacian (∇2ρ(r) > 0). These topological parameters showed that covalent bonding interactions are dominant in PdN and PdO bonds. However, PdN bonds have more covalent characters than PdO bonds, which is further confirmed by the ratio of local electron potential energy density to the local electron kinetic energy density (|V(r)|/G(r)) found to be higher for PdN bonds (1.1683–1.1993) as compared to PdO bonds (1.0689–1.0926). AIM and NBO reveal that shorter PdN and PdO bonds have higher interaction energies (Eint) and hence higher bond covalence.

Activating lattice oxygen redox reactions in metal oxides to catalyse oxygen evolution.

Understanding how materials that catalyse the oxygen evolution reaction (OER) function is essential for the development of efficient energy-storage technologies. The traditional understanding of the OER mechanism on metal oxides involves four concerted proton-electron transfer steps on metal-ion centres at their surface and product oxygen molecules derived from water. Here, using in situ 18O isotope labelling mass spectrometry, we provide direct experimental evidence that the O2 generated during the OER on some highly active oxides can come from lattice oxygen. The oxides capable of lattice-oxygen oxidation also exhibit pH-dependent OER activity on the reversible hydrogen electrode scale, indicating non-concerted proton-electron transfers in the OER mechanism. Based on our experimental data and density functional theory calculations, we discuss mechanisms that are fundamentally different from the conventional scheme and show that increasing the covalency of metal-oxygen bonds is critical to trigger lattice-oxygen oxidation and enable non-concerted proton-electron transfers during OER.

Enhancing thermoelectric performance in hierarchically structured BiCuSeO by increasing bond covalency and weakening carrier–phonon coupling

Improved thermoelectric performance of BiCuSeO via increased bond covalency and carrier mobility.

Spectral properties and solution behavior of gold(III) coordination compounds with water-soluble porphyrins

Gold(III) coordination compounds with three water-soluble porphyrins―5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TSPP4–), 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (H2TMPyP4+), and 5,10,15,20-tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin (H2TTMAPP4+)―have been studied. Complex [Au(TTMAPP)]5+ has been prepared for the first time. The analysis of coordination-induced shifts of proton signals in NMR spectra and intensities of Q bands in absorption spectra indicates the high degree of bond covalence in the studied metal porphyrins and a partial transfer of electron density from porphyrin to gold ion. The cationic complexes [Au(TMPyP)]5+ and [Au(TTMAPP)]5+ in aqueous solutions has been found to exist in monomeric form, while anionic complex [Au(TSPP)]3– undergoes dimerization upon growth of concentration and solution ionic strength. Equilibrium constant for dimerization has been calculated, the constant has been found to decrease when temperature rises. Thermodynamic parameters of dimerization process have been determined: ΔH° =–31.8 kJ/mol and ΔS° =–13.8 J/mol K.

EPR and optical studies of microwave synthesized glasses containing VO2+ ions: Meta and pyrophosphate regime

Glasses with compositions xV2O5 - (100 - x)[0.8NaPO3 - 0.2ZnO] (where 0.2 ≤ x ≤ 10 in mol%) were prepared by a new microwave heating method. The Electron Paramagnetic Resonance (EPR) spectra of vanadyl ions in the glasses exhibit a hyperfine structure. From EPR spectra the spin Hamiltonian parameters g∥, g⊥, A∥, A⊥, dipolar hyperfine coupling parameter (P), Fermi contact interaction parameter (K), Pβ2∗2 K and PK/γ have been evaluated. An increase in the ratio of Δg‖/Δg⊥ with an increase in V2O5 content shows that the tetragonal nature of the V4+O6 complex is enhanced. The increase in A'|| and P indicates that the 3dxy orbit contracts with V2O5 content. The molecular orbital coefficients α2, γ2 have been determined by correlating the EPR and optical absorption data. The values of α2 increase while γ2 decreases with an increase in V2O5 content, indicating the σ - bonding between the vanadium atom and the equatorial ligands decreases and the effect of π - bonding with the vanadyl oxygen increases. The bond ionicity and covalency of the glass network has been calculated using Pauling's electronegativity support the experimental findings. Observed variations in the optical band gap, refractive index, molar refraction, metallization criterion, electronic polarizability of the oxide ion and optical basicity are correlated with the glass structure. The photoluminescence (PL) excitation spectra reveal two individual peaks at 338 and 468 nm which are ascribed to the charge transfer reaction in [VO4]3− groups. An emission peak occurs at 531 nm and concentration quenching is seen beyond 0.5 mol% of V2O5.

Synthesis, X-ray Structures, Electronic Properties, and O2/NO Reactivities of Thiol Dioxygenase Active-Site Models.

Mononuclear non-heme iron complexes that serve as structural and functional mimics of the thiol dioxygenases (TDOs), cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO), have been prepared and characterized with crystallographic, spectroscopic, kinetic, and computational methods. The high-spin Fe(II) complexes feature the facially coordinating tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (Ph2TIP) ligand that replicates the three histidine (3His) triad of the TDO active sites. Further coordination with bidentate l-cysteine ethyl ester (CysOEt) or cysteamine (CysAm) anions yielded five-coordinate (5C) complexes that resemble the substrate-bound forms of CDO and ADO, respectively. Detailed electronic-structure descriptions of the [Fe(Ph2TIP)(LS,N)]BPh4 complexes, where LS,N = CysOEt (1) or CysAm (2), were generated through a combination of spectroscopic techniques [electronic absorption, magnetic circular dichroism (MCD)] and density functional theory (DFT). Complexes 1 and 2 decompose in the presence of O2 to yield the corresponding sulfinic acid (RSO2H) products, thereby emulating the reactivity of the TDO enzymes and related complexes. Rate constants and activation parameters for the dioxygenation reactions were measured and interpreted with the aid of DFT calculations for O2-bound intermediates. Treatment of the TDO models with nitric oxide (NO)-a well-established surrogate of O2-led to a mixture of high-spin and low-spin {FeNO}7 species at low temperature (-70 °C), as indicated by electron paramagnetic resonance (EPR) spectroscopy. At room temperature, these Fe/NO adducts convert to a common species with EPR and infrared (IR) features typical of cationic dinitrosyl iron complexes (DNICs). To complement these results, parallel spectroscopic, computational, and O2/NO reactivity studies were carried out using previously reported TDO models that feature an anionic hydrotris(3-phenyl-5-methyl-pyrazolyl)borate (Ph,MeTp-) ligand. Though the O2 reactivities of the Ph2TIP- and Ph,MeTp-based complexes are quite similar, the supporting ligand perturbs the energies of Fe 3d-based molecular orbitals and modulates Fe-S bond covalency, suggesting possible rationales for the presence of neutral 3His coordination in CDO and ADO.

Sensitivity Modulation of Upconverting Thermometry through Engineering Phonon Energy of a Matrix.

Investigation of the unclear influential factors to thermal sensing capability is the only way to achieve highly sensitive thermometry, which is greatly needed to meet the growing demand for potential sensing applications. Here, the effect from the phonon energy of a matrix on the sensitivity of upconversion (UC) microthermometers is elaborately discussed using a controllable method. Uniform truncated octahedral YF3:Er3+/Yb3+ microcrystals were prepared by a hydrothermal approach, and phase transformation from YF3 to YOF and Y2O3 with nearly unchanged morphology and size was successfully realized by controlling the annealing temperature. The phonon energies of blank matrixes were determined by FT-IR spectra and Raman scattering. Upon 980 nm excitation, phonon energy-dependent UC emitting color was finely tuned from green to yellow for three samples, and the mechanisms were proposed. Thermal sensing behaviors based on the TCLs (2H11/2/4S3/2) were evaluated, and the sensitivities gradually grew with the increase in the matrix's phonon energy. According to chemical bond theory and first-principle calculations, the most intrinsic factors associated with thermometric ability were qualitatively demonstrated through analyzing the inner relation between the phonon energy and bond covalency. The exciting results provide guiding insights into employing appropriate host materials with desired thermometric ability while offering the possibility of highly accurate measurement of temperature.

Effect of gamma irradiation on X-ray absorption andphotoelectron spectroscopy of Nd-doped phosphate glass.

X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) of Nd-doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of the L3-edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d5/2 peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy-dispersive X-ray spectroscopy measurements. The ratio of non-bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.

Al grain boundary segregations in doped intermetallic NiAl and their effect on brittleness at room temperature

The nature of intermetallic NiAl brittleness is investigated by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and electron energy-loss fine structure (EELFS) means. It is found that the reason for this phenomenon is the ordering of intermetallic NiAl, accompanied by the formation of aluminum structural segregations at grain boundaries. Doping with 0.1 wt % La transforms the atomic and electronic structures of grain boundaries, eliminating NiAl intergranular fracturing at room temperature. Doping is accompanied by Fermi level shifts and an increase in conduction electron density neff. These factors are responsible for the lower covalence of interatomic bonds in pure intermetallic NiAl. The effect A1 segregations have on the critical deformation of the generating grain boundary fracture in NiAl is discussed.

Pressure effect on superconductivity in FeSe0.5Te0.5

Due to the simple layered structure, isostructural FeSe and FeSe0.5Te0.5 are clue compounds for understanding the principal mechanisms of superconductivity in the family of Fe‐based superconductors. High‐pressure magnetic, structural and Mössbauer studies have been performed on single‐crystalline samples of superconducting FeSe0.5Te0.5 with Tc = 13.5 K. Susceptibility data have revealed a strong increase of Tc up to 19.5 K for pressures up to 1.3 GPa, followed by a plateau in the Tc(p) dependence up to 5.0 GPa. Further pressure increase leads to a disappearance of the superconducting state around 7.0 GPa. X‐ray diffraction and Mössbauer studies explain this fact by a tetragonal‐to‐hexagonal structural phase transition. Mössbauer parameters of the non‐superconducting high‐pressure phase indicate less covalency of FeSe bonds. Based on structural and susceptibility data, we conclude about a common character of Tc(p) diagrams for both FeSe and FeSe0.5Te0.5 superconductors.

(Invited) "Structure-Property", "Composition-Property" and "Property-Property" Relations As Useful Tools for Understanding of Optical Materials Performance

Continuously growing demand for optical materials used in various applications (such as solid state lighting, lasers, sensors, scintillators etc) stimulates active research aimed at the development of new materials and optimization/improvement of the existing ones. Systematic comparative studies of large groups of isostructural compounds or isoelectronic impurities can help in uncovering different “structure-property”, “composition-property”, and “property-property” relations, which can lead to a deeper understanding of optical materials operation and can be used as reliable guidelines identifying directions for a smart search for new materials with better performance. In the present work we discuss our recent results of application of several different approaches (crystal field theory, density functional theory (DFT)-based computational techniques, configurational coordinate model etc) to various groups of materials – pyrochlores, perovskites, garnets, spinels, chalcopyrites, III-V and II-VI semiconductors, pure and doped with transition metal and rare earth ions. Firstly, an empirical model was developed to express the lattice constants of isostructural cubic and tetragonal compounds in terms of ionic radii and electronegativities of constituting ions [1]. The average deviation between the experimental values of the lattice constants and those estimated from the proposed theory is of the order of 1 % only. The model not only allows to fit the lattice constants of the considered crystals, but also gives an opportunity to predict the lattice constants of new compounds and analyze the stability criteria for existing materials. Secondly, DFT-based calculations were employed to explain peculiar features of the Cr4+ and Mn4+ spectra in Y2Ti2O7 and Y2Sn2O7 pyrochlores. In particular, it has been shown that the blue shift of the 3d-ions absorption peaks in Y2Sn2O7 in comparison with Y2Ti2O7 (in spite of larger interionic separations in the former case) can be explained by increased ligands charge in Y2Sn2O7 because of a weaker overlap of the oxygen orbitals with completely filled 4d10 orbitals of Sn4+ [2]. Thirdly, careful examination of variation of energies of the spin-forbidden transitions of transition metal ions (Mn4+, Cr3+, Ni2+) in various solids allowed to relate those energies with the covalent effects experienced by those ions. In this connection, a clear link between the degree of covalency of chemical bonds and spatial arrangements of crystal lattice ions was established. These findings can help in search for new efficient red phosphors based on the Mn4+ ions [3]. Fourthly, DFT-based calculations of the structural, optical, electronic properties of chalcopyrites and II-VI (III-V) semiconductors revealed important changes of the band gap character (direct or indirect) or enhanced absorptivity with composition, which has direct influence on perspectives of applications of these materials for solar cell materials and/or LED devices [4]. All obtained results are compared with the corresponding experimental data; agreement between both sets of data is discussed. Predictive potential of the presented calculations and possibility of applications of the developed models to other systems are highlighted.

Role of composition, bond covalency, and short-range order in the disordering of stannate pyrochlores by swift heavy ion irradiation

${A}_{2}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{O}}_{7}$ $(A=\mathrm{Nd},\text{Sm},\text{Gd},\text{Er},\text{Yb},\text{and Y})$ materials with the pyrochlore structure were irradiated with 2.2 GeV Au ions to systematically investigate disordering of this system in response to dense electronic excitation. Structural modifications were characterized, over multiple length scales, by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. Transformations to amorphous and disordered phases were observed, with disordering dominating the structural response of materials with small $A$-site cation ionic radii. Both the disordered and amorphous phases were found to possess weberite-type local ordering, differing only in that the disordered phase exhibits a long-range, modulated arrangement of weberite-type structural units into an average defect-fluorite structure, while the amorphous phase remains fully aperiodic. Comparison with the behavior of titanate and zirconate pyrochlores showed minimal influence of the high covalency of the Sn-O bond on this phase behavior. An analytical model of damage accumulation was developed to account for simultaneous amorphization and recrystallization of the disordered phase during irradiation.

First principles calculations of SrZrO3 bulk and ZrO2-terminated (001) surface F centers

Using a supercell model and B3PW hybrid exchange-correlation functional in the framework of the density functional theory (DFT), as it is implemented in the CRYSTAL computer code, we performed ab initio calculations for the F-center located in the SrZrO3 bulk and on the ZrO2-terminated (001) surface. According to the results of performed relaxation of atoms around the defect, two nearest Zr and four Sr atoms are repulsed, but all oxygen atoms are attracted towards both, the bulk and (001) surface F-center. The displacement magnitudes of atoms surrounding the bulk F-center are smaller than around the (001) surface F-center. The B3PW calculated SrZrO3 bulk optical band gap (5.00 eV) is in a fair agreement with the experimental value of 5.6 eV. The ZrO2-terminated (001) surface optical band gap (4.63 eV) is smaller in regard to the bulk value. The bulk and (001) surface F-center bands in SrZrO3, calculated using 3 × 3 × 3 and 3 × 3 × 1 times expanded supercells, are located 1.12 and 0.93 eV under the conduction band bottom. The O vacancy in the SrZrO3 bulk attracts 1.25e, and even less, only 1.10e on the ZrO2-terminated (001) surface. Performed calculations reveal significant enhancement of the chemical bond covalency among the SrZrO3 bulk F-center and its nearest Zr atoms of 0.244e in comparison with the ideal SrZrO3 perovskite ZrO chemical bond covalency of 0.100e. Our detected defect formation energy for the F-center located on the ZrO2-terminated (001) surface 7.52 eV is somewhat smaller than in the SrZrO3 bulk 7.55 eV. Our calculated formation energy difference may trigger the segregation of the F-center from the SrZrO3 bulk towards the ZrO2-terminated (001) surface.

Water electrolysis on La(1-x)Sr(x)CoO(3-δ) perovskite electrocatalysts.

Perovskite oxides are attractive candidates as catalysts for the electrolysis of water in alkaline energy storage and conversion systems. However, the rational design of active catalysts has been hampered by the lack of understanding of the mechanism of water electrolysis on perovskite surfaces. Key parameters that have been overlooked include the role of oxygen vacancies, B–O bond covalency, and redox activity of lattice oxygen species. Here we present a series of cobaltite perovskites where the covalency of the Co–O bond and the concentration of oxygen vacancies are controlled through Sr2+ substitution into La1−xSrxCoO3−δ. We attempt to rationalize the high activities of La1−xSrxCoO3−δ through the electronic structure and participation of lattice oxygen in the mechanism of water electrolysis as revealed through ab initio modelling. Using this approach, we report a material, SrCoO2.7, with a high, room temperature-specific activity and mass activity towards alkaline water electrolysis.

Structure and magnetic interactions in (Sr, Sb)-doped lanthanum manganites

Ceramic samples La1−2xSr2xMn1−xSbxO3 (x≤0.2) have been studied by X-ray and neutron powder diffraction, magnetization measurements and charge density calculations have also been performed. The compounds are characterized by the rhombohedral structure at room temperature; temperature decrease causes structural transition to the orthorhombic structure. La1−2xSr2xMn1−xSbxO3 ceramics are characterized by homovalent manganese ions and have long range ferromagnetic order which gradually diminishes with the chemical substitution. It is considered that magnetic properties of the compounds are determined by the dominance of ferromagnetic superexchange interactions stabilized in the orbital disordered orthorhombic phase. Significant covalent component of the Mn–O chemical bonds contributes to the long-range ferromagnetic order of the compounds, the covalency of the chemical bonds is assumed to be isotropically distributed over the orthorhombic phase.

Oxyfluoroborate host glass for upconversion application: phonon energy calculation

Reducing the glass phonon energy is an essential procedure to achieve high efficient radiative upconversion process. The degree of covalence of chemical bonds is responsible for the high oscillator strength of intracenter transitions in rare-earth ions. So, conversion covalent to ionic glass character is proposed as a structure-sensitive criterion that controls the phonon energy of the glasses. A series of oxyfluoro aluminum-borate host glasses used for upconversion application is prepared by the conventional melt-quenching technique. Through lithium oxide substitution by lithium fluoride, the ionic-covalent property of Li+ ion successes to regulate the band gap energies of the studied glasses. Furthermore, a new method to determine the glass phonon energy is offered.

Use of (77)Se and (125)Te NMR Spectroscopy to Probe Covalency of the Actinide-Chalcogen Bonding in [Th(En){N(SiMe3)2}3](-) (E = Se, Te; n = 1, 2) and Their Oxo-Uranium(VI) Congeners.

Reaction of [Th(I)(NR2)3] (R = SiMe3) (1) with 1 equiv of either [K(18-crown-6)]2[Se4] or [K(18-crown-6)]2[Te2] affords the thorium dichalcogenides, [K(18-crown-6)][Th(η(2)-E2)(NR2)3] (E = Se, 2; E = Te, 3), respectively. Removal of one chalcogen atom via reaction with Et3P, or Et3P and Hg, affords the monoselenide and monotelluride complexes of thorium, [K(18-crown-6)][Th(E)(NR2)3] (E = Se, 4; E = Te, 5), respectively. Both 4 and 5 were characterized by X-ray crystallography and were found to feature the shortest known Th-Se and Th-Te bond distances. The electronic structure and nature of the actinide-chalcogen bonds were investigated with (77)Se and (125)Te NMR spectroscopy accompanied by detailed quantum-chemical analysis. We also recorded the (77)Se NMR shift for a U(VI) oxo-selenido complex, [U(O)(Se)(NR2)3](-) (δ((77)Se) = 4905 ppm), which features the highest frequency (77)Se NMR shift yet reported, and expands the known (77)Se chemical shift range for diamagnetic substances from ∼3300 ppm to almost 6000 ppm. Both (77)Se and (125)Te NMR chemical shifts of given chalcogenide ligands were identified as quantitative measures of the An-E bond covalency within an isoelectronic series and supported significant 5f-orbital participation in actinide-ligand bonding for uranium(VI) complexes in contrast to those involving thorium(IV). Moreover, X-ray diffraction studies together with NMR spectroscopic data and density functional theory (DFT) calculations provide convincing evidence for the actinide-chalcogen multiple bonding in the title complexes. Larger An-E covalency is observed in the [U(O)(E)(NR2)3](-) series, which decreases as the chalcogen atom becomes heavier.

Redox flexibility of iron complexes supported by sulfur-based tris(o-methylenethiophenolato)amine relative to its tripodal oxygen-based congener.

Tripodal ligands designed to generate a local C3 symmetry have resulted in novel types of metal complexes that feature unusual bonding and electronic properties. However, most complexes reported to date are characterised by strong field ligands that enforce low or intermediate-spin states for the metal centres. Moreover, anionic sulfur-based tripodal ligands are particularly scarce due to their challenging synthesis. In this context, we herein report the synthesis, spectral characterization, structural, and electronic properties of an iron complex supported by the tripodal, trianionic ligand [N(CH2ArS)3](3-) as the trigonal-bipyramidal complexes [Fe{N(CH2ArS)3}(X)] ((X), X = DMSO, THF). The solid-state structures reveal local C3v symmetry around the Fe(3+) ions, while electron spin resonance measurements established a high-spin state (S = 5/2). Electrochemical studies demonstrate the redox flexibility of the FeS3 fragment by direct comparison with the oxygen-based analogue N(CH2ArOH)3, which displays an irreversible reduction; in contrast, (THF) has a reversible Fe(3+)/Fe(2+) redox process at -0.83 V (relative to the ferrocenium/ferrocene redox couple). The high spin and redox properties of (THF) are attributable to the weak ligand field provided by the NS3 fragment, as confirmed by the electronic structure calculated by density functional theory, which reveals substantial electronic delocalisation and covalency of the Fe-S bonds in (X).

Assessing covalency in equatorial U-N bonds: density based measures of bonding in BTP and isoamethyrin complexes of uranyl.

Calculations performed at the density functional level of theory have been used to investigate complexes of uranyl with the expanded porphyrin isoamethyrin and the bis-triazinyl-pyridine (BTP) ligands, the latter of which is well-known to be effective in the separation of trivalent lanthanides and actinides. Analysis has been performed using a range of density-based techniques, including the Quantum Theory of Atoms in Molecules (QTAIM), the Electron Localisation Function (ELF) and the reduced density gradient (RDG). The effects of peripheral alkyl substituents on UO2-isoamethyrin, known to be vital for proper replication of the experimental geometry, are considered. Evidence for comparable amounts of covalent character has been found in the largely ionic U-N bonds of UO2-isoamethyrin and [UO2(BTP)2](2+) and examination of the variation in the electronic characteristics of the uranyl unit upon complexation in both of these cases reveal striking similarities in the nature of the U-N bonding and the effect of this bonding on the U-Oyl interaction, as well as evidence of donation into the U-N bonding region from the uranyl unit itself.

Tuning the Mn valence state in new Ca(0.66)Mn(2-x)Al(x)O4 (x≤ 0.4) oxides: impact on magnetic and redox properties.

New Ca(0.66)Mn(2-x)Al(x)O4 (x≤ 0.4) solid solutions crystallizing with the CaFe2O4-type structure (SG: Pnma) were synthesized for the first time by the glycine-nitrate process. The structures were determined on the basis of XRD Rietveld analysis and electron diffraction investigation. While the CaMn3O6 ('Ca(0.66)Mn2O4') oxide adopts a monoclinic unit cell, the Al substitution for Mn (x = 0.2, 0.4) leads to an orthorhombic cell with only two Mn atomic positions, with different valence states, and 33% of Ca sites empty. The Ca molar concentration decreases down to 0.6 in order to increase the Mn valence leading to a phase mixture, whereas a slight Ca content increase up to 0.7 leads to a decrease of Mn valence in the pure phase. The Al(3+) ions are located at a specific Mn site because their ionic radii are close to that of Mn(4+) and a more isotropic environment. The unit cell parameters and volume strongly decrease for a low Al content and tend to an asymptotic value of x = 0.33-0.4, around the limit of solubility. As the Al content increases, the Mn valence state in the same slightly distorted octahedral site increases up to 4+ whereas the other octahedral site is highly elongated and corresponds mainly to Jahn-Teller Mn(3+). At x = 0.33, these two Mn sites correspond to Mn(4+) and Mn(3+) respectively. Moreover, the aluminium content increase induces a weakening of the global antiferromagnetic long range interactions between the ferromagnetic chains. The Al substitution leads to the change of the Mn valence distribution as well as the unit cell symmetry of the CaMn3O6 phase. These 1D tunnel networks stabilizing the Mn(3+)/Mn(4+) valence states can be reduced under Ar/5%H2 between T = 300 °C and T = 600 °C (heating rate = 2 °C min(-1)) into pure Mn(2+) rocksalt solid solution despite the large difference in ionic radii. The re-oxidation leads to the same CaFe2O4-type structure and several redox cycles can be operated. The relationship between the two double chains of the edge-sharing octahedral sites and the rocksalt-type framework is clear and should appear as the driving force for the structural transformation during the reduction/oxidation processes. Finally, Al substitution allows an increasing of the Mn-O bond covalence and consequently the reduction in temperature.