HAp‐encapsulated γ‐Fe2O3‐supported dual acidic heterogeneous catalyst for highly efficient one‐pot synthesis of benzoxanthenones and 3‐pyranylindoles

A novel method is reported for the synthesis of benzoxanthenone and 3‐pyranylindole derivatives via one‐pot three‐component reactions using a newly synthesized HAp‐encapsulated γ‐Fe₂O₃‐supported dual acidic heterogeneous catalyst, as a reusable and highly efficient nanocatalyst. In this protocol the use of the nanocatalyst provided a green, useful and rapid method to generate products in short reaction times (4–20 min) and in excellent yields (87–96%). The paramagnetic nature of the catalyst provided a simple, trouble‐free and facile approach for the separation of the catalyst by applying an external magnet, and it could be used in eight cycles without significant loss in catalytic efficiency.     

Eco‐friendly synthesis of 3,4‐dihydroquinoxalin‐2‐amine,diazepine‐tetrazole and benzodiazepine‐2‐carboxamide derivatives with the aid of MCM‐48/H5PW10V2O40

A heterogeneous material composed of MCM‐48/H₅PW₁₀V₂O₄₀ was produced and used as an efficient, eco‐friendly and highly recyclable catalyst for the one‐pot and multicomponent synthesis of 3,4‐dihydroquinoxalin‐2‐amine, diazepine‐tetrazole and benzodiazepine‐2‐carboxamide derivatives in aqueous media and at room temperature with high yields in short reaction times (40–60 min). The recoverable catalyst was easily recycled at least five times without any loss of catalytic activity. The structures of obtained products were confirmed using ¹H NMR and ¹³C NMR spectra.     

Perylene diimide‐modified magnetic γ‐Fe2O3/CeO2 nanoparticles as peroxidase mimics for highly sensitive colorimetric detection of Vitamin C

Perylene diimide‐modified magnetic γ‐Fe₂O₃/CeO₂ nanoparticles (γ‐Fe₂O₃/CeO₂‐PDI) were prepared and exhibited excellent peroxidase‐like activity. The samples were characterized by HR‐TEM, XRD, Raman, N₂ adsorption, magnetic strength and XPS. The obtained γ‐Fe₂O₃/CeO₂‐PDI had size of 10~20 nm with high specific surface area of 77 m²/g, and could be easily separated from the aqueous solution by using a magnet, which are in favor of its practical application. Due to the decoration of PDI, the γ‐Fe₂O₃/CeO₂‐PDI possessed more surface defects (Ce³⁺) and active oxygen species than that of γ‐Fe₂O₃/CeO₂, resulting in the outstanding catalytic performance. And the composite catalyst also showed highly sensitive and selectivity toward VC with a limit of detection of 0.45 μM. Based on the fluorescent results, a possible hydroxyl radical (?OH) catalytic mechanism was proposed. It is believed that the as‐prepared γ‐Fe₂O₃/CeO₂‐PDI nanoparticles are promising biosensors applied for biomedical and food analysis.     

Green bio‐based synthesis of Fe2O3@SiO2‐IL/Ag hollow spheres and their catalytic utility for ultrasonic‐assisted synthesis of propargylamines and benzo[b]furans

A novel magnetic hybrid system containing nano‐magnetic Fe₂O₃ hollow spheres, silica shell, [pmim]Cl ionic liquid and silver nanoparticles was synthesized and characterized. The silver nanoparticles were prepared via biosynthesis using Achillea millefolium flower as reducing and stabilizing agent. The hybrid system was successfully used as an efficient and reusable catalyst for promoting green ultrasonic‐assisted A³ and KA² coupling reactions as well as benzo[b]furan synthesis. It was found that decoration of the magnetic core with non‐magnetic moieties decreased the maximum saturation magnetization. However, the catalyst was still superparamagnetic and could be simply separated from the reaction mixture using an external magnet. The heterogeneous nature of the catalyst was also confirmed by studying its reusability and stability and the leaching of silver. Use of aqueous media, high yields, short reaction times, broad substrate tolerance and low required amount of catalyst are the merits of this protocol.     

NH2SO3H–SiO2 as a new water‐compatible,recyclable heterogeneous catalyst for the synthesis of novel (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction

NH₂SO₃H–SiO₂/water as a novel catalytic system was used for the synthesis of (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction at reflux conditions. The methodology was of general applicability and the catalyst exhibited activity up to five cycles. The catalyst was characterized for the first time using FT‐IR, X‐ray diffraction and scanning electron microscopic–energy dispersion analytical X‐ray. The stability of the catalyst was evaluated by differential scanning calorimetry and TGA/differential thermal analysis. High efficiency of the catalyst along with its recycling ability and the rather low loading demonstrated in reactions are the merits of the presented protocol. Copyright © 2013 John Wiley & Sons, Ltd.     

Four oxoindole‐linked α‐alkoxy‐β‐amino acid derivatives

Four structures of oxoindolyl α‐hydroxy‐β‐amino acid derivatives, namely, methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐methoxy‐2‐phenylacetate, C₂₄H₂₈N₂O₆, (I), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐ethoxy‐2‐phenylacetate, C₂₅H₃₀N₂O₆, (II), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐[(4‐methoxybenzyl)oxy]‐2‐phenylacetate, C₃₁H₃₄N₂O₇, (III), and methyl 2‐[(anthracen‐9‐yl)methoxy]‐2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐phenylacetate, C₃₈H₃₆N₂O₆, (IV), have been determined. The diastereoselectivity of the chemical reaction involving α‐diazoesters and isatin imines in the presence of benzyl alcohol is confirmed through the relative configuration of the two stereogenic centres. In esters (I) and (III), the amide group adopts an anti conformation, whereas the conformation is syn in esters (II) and (IV). Nevertheless, the amide group forms intramolecular N—H...O hydrogen bonds with the ester and ether O atoms in all four structures. The ether‐linked substituents are in the extended conformation in all four structures. Ester (II) is dominated by intermolecular N—H...O hydrogen‐bond interactions. In contrast, the remaining three structures are sustained by C—H...O hydrogen‐bond interactions.     

H3PW12O40/mpg‐C3N4 as an efficient and reusable catalyst in the alkylation of o‐xylene and styrene

A heterogeneous catalyst (HPW/mpg‐C₃N₄) for the alkylation of o‐xylene and styrene reaction was acquired by the immobilization of phosphotungstic acid (HPW) on mesoporous graphitic carbon nitride (mpg‐C₃N₄) through electrostatic interaction. The results of Fourier transform infrared spectroscopy (FT‐IR), X‐ray powder diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) proved that HPW was successfully immobilized on the protonated mpg‐C₃N₄ by electrostatic interaction. The textural properties and morphology of HPW/mpg‐C₃N₄ were characterized by N₂ adsorption–desorption, scanning electron microscopy (SEM). Among them, 40% HPW/mpg‐C₃N₄ displays the best catalytic performance in the alkylation reaction with 91.8% yield and 96.5% selectivity to 1, 2‐diphenylethylane. Moreover, protonated mpg‐C₃N₄ not only displays as a support to facilitate great dispersion of HPW but also promotes the alkylation product diffusion effectively. Besides, the HPW/mpg‐C₃N₄ catalyst could be recycled easily without significant loss of catalytic activity, which is demonstrate by the recyclability of HPW/mpg‐C₃N₄ catalyst test.     

Tetrylenes chelated by bifunctional β‐diketiminate ligand: structure and possible applications

The synthesis and structure of heteroleptic tetrylenes containing bifunctional β‐diketiminate ligand are reported. Compounds were prepared via a protolytic reaction of free β‐diketimine {N‐[(2‐MeO)C₆H₅]}N═C(Me)CH═C(Me)N(H){N′‐[(2‐MeO)C₆H₅]} (L^COH) and {N‐[(2‐MeO)C₆H₅]}N?CHCH?CHN(H){N′‐[(2‐MeO)C₆H₅]} (L^HOH), respectively, with corresponding bis(amide) – M[N(SiMe₃)₂]₂ (M = Ge, Sn, Pb) – in equimolar ratio or via the salt elimination route from lithium precursors generated from L^HOH/L^COH species and slight excess of SnCl₂ or GeCl₂.dioxane complex. Only heteroleptic complexes were obtained by the mentioned methods. Products were characterized by multinuclear NMR spectroscopy techniques and structures of four of them have been determined by X‐ray diffraction methods. Complexes L^HOGeCl and L^COSnN(SiMe₃)₂ crystallize as monomers with the three‐coordinated metal centres by one chloro or amido ligand and one bidentate β‐diketiminato unit, in contrast to the structure of L^COSnCl, which reveals a dimeric character and compound L^COPbN(SiMe₃)₂, where the central atom of lead is five‐coordinated by methoxy groups of the ligand. Complex L^COSnN(SiMe₃)₂ was tested as a catalyst for polymerization of various epoxides_. Copyright © 2014 John Wiley & Sons, Ltd.     

Silver,iron, and nickel immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 MNPs catalyzed one‐pot five‐component reactions for the synthesis of tetrahydropyridines by tandem condensation of amines,aldehydes, and methyl acetoacetate

In this study, Ag, Ni²⁺, and Fe²⁺ immobilized on hydroxyapatite‐core‐shell γ‐Fe₂O₃ nanoparticles (γ‐Fe₂O₃@HAp‐Ag, γ‐Fe₂O₃@HAp‐Ni²⁺, and γ‐Fe₂O₃@HAp‐Fe²⁺) as a new and reusable Lewis acid magnetic nanocatalyst was successfully synthesized and reported for an atom economic, extremely facile, and environmentally benign procedure for the synthesis of highly functionalized tetrahydropyridines derivatives 4a‐t is described by one‐pot five‐component reaction of 2 equiv of aldehydes 1 , 2 equiv of amines 2 , and 1 equiv of methyl acetoacetate 3 in EtOH at room temperature in good to high yields and short reaction time. The presented methodology offers several advantages such as easy work‐up procedure, reusability of the magnetic nanocatalyst, operational simplicity, green synthesis avoiding toxic reagents and solvent, mild reaction conditions, and no tedious column chromatographic separation.     

Novel Flower‐Like Ag‐SiO2‐MgO‐Al2O3 Material: Preparation,Characterization and Catalytic Application in Methanol Dehydrogenation

Catalytic direct dehydrogenation of methanol to formaldehyde was carried out over Ag‐SiO₂‐MgO‐Al₂O₃ catalysts prepared by sol‐gel method. The optimal preparation mass fractions were determined as 8.3% MgO, 16.5% Al₂O₃ and 20% silver loading. Using this optimum catalyst, excellent activity and selectivity were obtained. The conversion of methanol and the selectivity to formaldehyde both reached 100%, which were much higher than other previously reported silver supported catalysts. Based on combined characterizations, such as X‐ray diffraction (XRD), scanning electronic microscopy (SEM), diffuse reflectance ultraviolet‐visible spectroscopy (UV‐Vis, DRS), nitrogen adsorption at low temperature, temperature programmed desorption of ammonia (NH₃‐TPD), desorption of CO₂ (CO₂‐TPD), etc., the correlation of the catalytic performance to the structural properties of the Ag‐SiO₂‐ MgO‐Al₂O₃ catalyst was discussed in detail. This perfect catalytic performance in the direct dehydrogenation of methanol to formaldehyde without any side‐products is attributed to its unique flower‐like structure with a surface area less than 1 m²/g, and the strong interactions between neutralized support and the nano‐sized Ag particles as active centers.     

Magnetically separable g‐C3N4 hybrid nanocomposite: Highly efficient and eco‐friendly recyclable catalyst for one‐pot synthesis of α‐aminonitriles

A magnetically separable graphitic carbon nitride nanocomposite (Fe₃O₄/g‐C₃N₄) as a catalyst for the three‐component condensation reactions of carbonyl compounds, amines and trimethylsilylcyanide was thoroughly investigated. The reaction of these three components was found to be efficient, economical and green and took place in the presence of a catalytic amount of the magnetically separable catalyst to yield the corresponding α‐aminonitriles in good to excellent yields. The prepared nanocomposite was characterized using scanning electron microscopy and energy‐dispersive X‐ray and Fourier transform infrared spectroscopies. The nanocomposite was also found to be reusable could be recovered easily and reused several times without distinct deterioration in its catalytic activity.     

Ultrasound‐Assisted Synthesis of 6‐Methyl‐1,2,3,4‐tetrahydro‐N‐aryl‐2‐oxo/thio‐4‐arylpyrimidine‐5‐carboxamides Catalyzed by Uranyl Nitrate Hexahydrate

An efficient and simple method developed for the synthesis of 6‐methyl‐1,2,3,4‐tetrahydro‐N‐aryl‐2‐oxo/thio‐4‐arylpyrimidine‐5‐carboxamide derivatives ( 4a‐o ) using UO₂(NO₃)₂.6H₂O catalyst under conventional and ultrasonic conditions. The ultrasound irradiation synthesis had shown several advantages such as milder conditions, shorter reaction times and higher yields. The structures of all the newly synthesized compounds have been confirmed by FT‐IR, ¹H NMR, ¹³C NMR and mass spectra.     

Ammine(2,2′‐bipyridine‐κ2N,N′)silver(I) nitrate: a dimer formed by π–π stacking and ligand‐unsupported Ag...Ag interactions

Reaction of AgNO₃ and 2,2′‐bipyridine (bipy) under ultrasonic treatment gave the title compound, [Ag(C₁₀H₈N₂)(NH₃)]NO₃. The crystal structure consists of dimers formed by two symmetry‐related Ag^I–bipy monomers connected through intra‐dimer π–π stacking and ligand‐unsupported Ag...Ag interactions. A crystallographic C2 axis passes through the mid‐point of and is perpendicular to the Ag...Agⁱ(−x + 1, y, −z + ) axis. In addition, each Ag^I cation is coordinated by one chelating bipy ligand and one ammine ligand, giving a trigonal coordination environment capped by the symmetry‐equivalent Ag atom. Molecules are assembled by Ag...Ag, π–π, hydrogen‐bond (N—H...O and C—H...O) and weak Ag...π interactions into a three‐dimensional framework. Comparing the products synthesized under different mechanical treatments, we found that reaction conditions have a significant influence on the resulting structures. The luminescence properties of the title compound are also discussed.     

A two‐dimensional silver(I) coordination polymer constructed from 4‐aminophenylarsonate and triphenylphosphane: poly[[(μ3‐4‐aminophenylarsonato‐κ3N:O:O)(triphenylphosphane‐κP)silver(I)] monohydrate]

The title compound, {[Ag(C₆H₇AsNO₃)(C₁₈H₁₅P)]·H₂O}_n, has been synthesized from the reaction of 4‐aminophenylarsonic acid with silver nitrate, in aqueous ammonia, with the addition of triphenylphosphane (PPh₃). The Ag^I centre is four‐coordinated by one amino N atom, one PPh₃ P atom and two arsonate O atoms, forming a severely distorted [AgNPO₂] tetrahedron. Two Ag^I‐centred tetrahedra are held together to produce a dinuclear [Ag₂O₂N₂P₂] unit by sharing an O–O edge. 4‐Aminophenylarsonate (Hapa⁻) adopts a μ₃‐κ³N:O:O‐tridentate coordination mode connecting two dinuclear units, resulting in a neutral [Ag(Hapa)(PPh₃)]_n layer lying parallel to the (10) plane. The PPh₃ ligands are suspended on both sides of the [Ag(Hapa)(PPh₃)]_n layer, displaying up and down orientations. There is an R₂²(8) hydrogen‐bonded dimer involving two arsonate groups from two Hapa⁻ ligands related by a centre of inversion. Additionally, there are hydrogen‐bonding interactions involving the solvent water molecules and the arsonate and amine groups of the Hapa⁻ ligands, and weak π–π stacking interactions within the [Ag(Hapa)(PPh₃)]_n layer. These two‐dimensional layers are further assembled by weak van der Waals interactions to form the final architecture.     

Catalytic Oxidation of Methane to C2‐C4 Hydrocarbons over CeO2 Promoted W‐Mn/SiO2 Catalysts at Higher Pressure

CeO₂‐promoted Na‐Mn‐W/SiO₂ catalyst has been studied for catalytic oxidation of methane in a micro‐stainless‐steel reactor at elevated pressure. The effect of operating conditions, such as GHSV, pressure and CH₄/O₂ ratio, has been investigated. 22.0% CH₄ conversion with 73.8% C₂‐C₄ selectivity (C₂/C₃/C₄ = 3.8/1.0/3.6) was obtained at 1003 K, 1.5 × 10⁵ h^?;1 GHSV and 1.0 MPa. The results show: Elevated pressure disadvantages the catalytic oxidation of methane to C₂‐C₄ hydrocarbons. Large amounts of C₃ and C₄ hydrocarbons are observed. The unfavorable effects of elevated pressure can be overcome by increasing GHSV; the reaction is strongly dependent on the operating conditions at elevated pressure, particularly dependent on GHSV and ratio of CH₄/O₂. Analyses by means of XRD, XPS and CO₂‐TPD show that CO₂ produced from the reaction makes a weakly poisoning capacity of the catalyst; information of changeful valence on Ce and Mn was detected over the near‐surface of the Ce‐Na‐W‐Mn/SiO₂ catalyst; the existence of Ce³⁺/Ce⁴⁺ and Mn²⁺/Mn³⁺ ion couple supported that the reaction over the catalyst followed the Redeal‐Redox mechanism. Oxidative re‐coupling of C₂H₆ and CH₄ in gas phase or over surface of catalyst produces C₃ or C₄ hydrocarbons.     

Efficient conversion of fructose to 5‐hydroxymethylfurfural by functionalized γ‐Al2O3 beads

Millimeter size γ‐Al₂O₃ beads were prepared by alginate assisted sol–gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized γ‐Al₂O₃ bead catalysts for fructose dehydration to 5‐hydroxymethylfurfural (5‐HMF). Experiment results showed that the porous structure of γ‐Al₂O₃ beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of γ‐Al₂O₃ beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and ‐SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C₁₆‐SO₃H‐γ‐Al₂O₃–650°C exhibited the highest yield of 5‐HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H₂O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110°C and reaction time of 4 hr.     

Atmospheric reactivity of ethylene catalyzed by β‐diketiminato Ni(II)/methylaluminoxane system

Atmospheric ethylene reactions were studied with backbone fluorinated β‐diketiminato Ni(II) complexes CH{C(CF₃)NAr}₂NiBr (1, Ar = 2,6‐Me₂C₆H₃, and 2 2,6‐ⁱPr₂C₆H₃) activated by methylaluminoxane (MAO). The catalytic systems exhibit the characteristics of catalyzing simultaneously polymerization and oligomerization of ethylene, indicating different active species involved in the reaction system. In an effort to investigate the alkylation species involved in the β‐diketiminato nickel (II)/MAO system, the reaction of 1 with methylaluminoxane were studied. With ¹⁹F{¹H NMR} spectra, two sets of new signals different from 1 were presented. Two alkylation products were proposed precursors of active species for producing oligomer and polymer of ethylene in the β‐diketiminato Ni(II)/MAO system. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrocatalysis of N2 to NH3 by HKUST‐1 with High NH3 Yield

Electrolytic ammonia synthesis from nitrogen at ambient conditions is appearing as a promising alternative to the Haber‐Bosch process which is consuming high energy and emitting CO₂. Here, a typical MOF material, HKUST‐1 (Cu?BTC, BTC=benzene‐1,3,5‐tricarboxylate), was selected as an electrocatalyst for the reaction of converting N₂ to NH₃ under ambient conditions. At ?0.75 V vs. reversible hydrogen electrode, it achieves excellent catalytic performance in the electrochemical synthesis of ammonia with high NH₃ yield (46.63 μg h^?1 mg^?1 _cat. or 4.66 μg h^?1 cm^?2) and good Faraday efficiency (2.45%). It is indicated that the good performance of the HKUST‐1 catalyst may originate from the formation of Cu(I). In addition, the catalyst also has good selectivity for N₂ to NH₃.     

2, 4‐Dimethylpenta‐1, 3‐dien‐ und 2, 4‐Dimethylpentadienyl‐Komplexe des Rhodiums und Iridiums

2, 4‐Dimethylpenta‐1, 3‐diene and 2, 4‐Dimethylpentadienyl Complexes of Rhodium and Iridium The complexes [(η⁴‐C₇H₁₂)RhCl]₂ ( 1 ) (C₇H₁₂ = 2, 4‐dimethylpenta‐1, 3‐diene) and [(η⁴‐C₇H₁₂)₂IrCl] ( 2 ) were obtained by interaction of C₇H₁₂ with [(η²‐C₂H₄)₂RhCl]₂ and [(η²‐cyclooctene)₂IrCl]₂, respectively. The reaction of 1 or 2 with CpTl (Cp = η⁵‐C₅H₅) yields the compounds [CpM(η⁴‐C₇H₁₂)] ( 3a : M = Rh; 3b : M = Ir). The hydride abstraction at the pentadiene ligand of 3a , b with Ph₃CBF₄ proceeds differently depending on the solvent. In acetone or THF the “half‐open” metallocenium complexes [CpM(η⁵‐C₇H₁₁)]BF₄ ( 4a : M = Rh; 4b : M = Ir) are obtained exclusively. In dichloromethane mixtures are produced which additionally contain the species [(η⁵‐C₇H₁₁)M(η⁵‐C₅H₄CPh₃)]BF₄ ( 5a : M = Rh; 5b : M = Ir) formed by electrophilic substitution at the Cp ring, as well as the η³‐2, 4‐dimethylpentenyl compound [(η³‐C₇H₁₃)Rh{η⁵‐C₅H₃(CPh₃)₂}]BF₄ ( 6 ). By interaction of 2, 4‐dimethylpentadienyl potassium with 1 or 2 the complexes [(η⁴‐C₇H₁₂)M(η⁵‐C₇H₁₁)] ( 7a : M = Rh; 7b : M = Ir) are generated which show dynamic behaviour in solution; however, attempts to synthesize the “open” metallocenium cations [(η⁵‐C₇H₁₁)₂M]⁺ by hydride abstraction from 7a , b failed. The new compounds were characterized by elemental analysis and spectroscopically, 4b and 5a also by X‐ray structure analysis.     

Investigations of the local distortions and EPR parameters for Cu2+ in xNa2O‐(30–x)K2O‐70B2O3 (5 ≤ x ≤ 25 mol%) glasses

The local distortions and electron paramagnetic resonance parameters for Cu²⁺ in the mixed alkali borate glasses xNa₂O‐(30–x)K₂O‐70B₂O₃ (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na₂O compositions x. Owing to the Jahn–Teller effect, the octahedral [CuO₆]¹⁰⁻ clusters show significant tetragonal elongation ratios p ~19% along the C₄ axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi‐linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi‐linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi‐linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal‐fields and the electronic cloud distribution around Cu²⁺ with the variation of the composition of Na₂O.