Document Type : Research Paper
Authors
Department of Chemistry, College of Science, University of Thi-Qar, Thi-Qar 64001, Iraq
Abstract
Keywords
INTRODUCTION
Nanocrystalline coordination compounds occupy a privileged position at the interface between molecular chemistry and materials science: their physical properties (optical, redox, magnetic, thermal) emerge not only from the molecular architecture, but also from the size and strain of the crystallites that they form in the solid state. For copper(II) β-diketonate frameworks in particular, the cooperative behaviour between coordinated metal centre, chelating ligand and bulky axial donor controls both the intramolecular electronic structure and the inter-molecular packing geometry that governs nano-domain formation [1–4].
Among redox-active building blocks, viologen (4,4ʹ-bipyridinium) derivatives are unique. The dication V²⁺ is reduced reversibly to a violet radical cation V•⁺ that, at sufficient concentration, dimerizes through non-covalent π–π interaction to a diamagnetic π-dimer (V)₂²⁺ [5–7]. When two viologen radicals are tethered through a flexible spacer or coordinated as axial ligands to a Cu(II) centre, the dimerization can be intramolecular (within a single molecule) or intermolecular (between two complex units). This switchable contraction–elongation has motivated their incorporation into electrochromic devices, redox-flow batteries and molecular memory elements [8–11].
Schiff bases derived from β-keto-esters and primary amines are an attractive equatorial scaffold for Cu(II): they enforce a robust square-planar N₂O₂ chelate, leave the axial positions of Cu(II) accessible to a fifth donor, and deliver photophysical signatures that report on coordination changes [12–15]. Halogenation of the ester moiety (replacing the methyl by a chloromethyl group) modifies both the steric profile and the local dipole, and consequently the crystal packing and lattice strain [16,17]. Yet no systematic, nano-scale structural investigation of chlorinated Cu(II) bis(keto-imino) complexes carrying axial mono- or bis-viologen units has been reported.
In the present work we (i) synthesized the chlorinated Schiff base (Z)-ethyl 4-chloro-3-(phenylimino)butanoate (EClN), its parent complex CuEClN and four axially coordinated adducts with pyridine, 4,4ʹ-bipyridine, C₁V⁺.PF₆⁻ and V₂²⁺.2PF₆⁻; (ii) extracted nanocrystalline parameters — average crystallite size D and microstrain ε — from powder XRD using both Scherrer and Williamson–Hall models, and correlated them with the size, charge and rigidity of the axial donor; (iii) corroborated the W–H trend by FE-SEM imaging at the nano/micro scale; and (iv) demonstrated, by chemical reduction with activated zinc and by cyclic voltammetry, the operation of redox-triggered π-dimerization switches centred on the axial viologen, monitored in real time by UV-Visible spectroscopy.
MATERIALS AND METHODS
Materials and instrumentation
Aniline, ethyl 4-chloroacetoacetate, copper(II) acetate monohydrate, pyridine, 4,4ʹ-bipyridine, methyl iodide and 1,3-dibromopropane were of analytical grade and used as received. Solvents (ethanol, methanol, DMF, DMSO, DCM, acetonitrile, diethyl ether) were used without further purification. KPF₆ was supplied by Sigma-Aldrich. FT-IR spectra were recorded on a Perkin-Elmer Tensor-27 (Bruker) spectrometer using KBr discs in the 4000–400 cm⁻¹ range (Department of Chemistry, University of Thi-Qar). ¹H-NMR spectra were measured on a Bruker Ascend 400 MHz instrument in DMSO-d₆ (College of Education for Pure Sciences, University of Basrah). LC-MS spectra were acquired on an Agilent 5973 Network MS detector (EI, 70 eV; mobile phase MeOH/H₂O) at the University of Tehran. UV-Visible spectra were measured on a PG-Instruments T90+ spectrophotometer using a 1 cm quartz cell. Thermogravimetric and DTA traces were recorded on a TA SDT Q600 instrument at a heating rate of 10 °C min⁻¹ in air or argon. Powder XRD patterns were collected on a PANalytical diffractometer using Cu Kα radiation (λ = 1.5405 Å) over 2θ = 5–80°. Field-emission scanning electron microscopy (FE-SEM) and EDS measurements were performed at 20 kV at the University of Tehran. Cyclic voltammetry was carried out on a PARSTAT 4000 (AMETEK, France) under argon at room temperature, using a three-electrode cell (3 mm vitreous carbon working electrode, Pt wire counter, Ag pseudo-reference) in DMF + 0.1 M tetra-n-butylammonium perchlorate (TBAP) at 100 and 300 mV s⁻¹.
Synthesis of the viologen building blocks
C₁V⁺.PF₆⁻ and V₂²⁺.2PF₆⁻ were prepared in two steps following the reported procedure [11,12]. Briefly, methyl iodide (0.39 mL, 6.4 mmol) was added to 4,4ʹ-bipyridine (1.0 g, 6.4 mmol) in 10 mL of DCM and stirred at room temperature for 24 h. The yellowish-orange solid was filtered and recrystallized from methanol to give C₁V⁺.I⁻ (1.0 g, 61 %, m.p. 248 °C). Anion exchange in water with saturated aqueous KPF₆ furnished C₁V⁺.PF₆⁻ as a white precipitate. The bis-viologen V₂²⁺.2Br⁻ was obtained from 4,4ʹ-bipyridine (2.0 g, 12.8 mmol, 2 eq) and 1,3-dibromopropane (0.65 mL, 6.4 mmol, 1 eq) in 20 mL of acetonitrile at 70 °C for 24 h, and then converted to V₂²⁺.2PF₆⁻ by anion exchange (yield 1.0 g, 48 %).
Synthesis of (Z)-ethyl 4-chloro-3-(phenylimino)butanoate (EClN)
Freshly distilled aniline (2 mL, 2.06 g, 0.022 mol, 1 eq) was added drop-wise to a solution of ethyl 4-chloroacetoacetate (2.90 mL, 0.020 mol, 1 eq) in absolute ethanol. The mixture was refluxed for 6 h and the progress monitored by TLC (ethyl acetate/benzene 4:6). The crude oil was air-dried and recrystallized from benzene/hexane (1:1) to afford EClN as a dark-brown solid. Yield: 3.0 g, 68 %; m.p. 160 °C; soluble in EtOH, MeOH, DCM, DCE, CHCl₃, acetone, benzene, DMF and DMSO; insoluble in n-hexane. UV-Vis (DMF, 0.02 mM): λ_max / nm (ε / M⁻¹ cm⁻¹) = 303 (11 450), 427 (1 100). FT-IR (KBr, cm⁻¹): 3041 ν(=C–H); 2929, 2900, 2830 ν(C–H); 1733 ν(C=O); 1696 ν(C=N); 1614–1495 ν(C=C); 1220–1027 ν(C–O). ¹H-NMR (400 MHz, DMSO-d₆): δ / ppm = 7.5 (d, 2H), 7.4 (d, 2H), 7.5 (t, 1H), 4.1 (s, 2H, ClCH₂), 3.4 (q, 2H), 1.1 (t, 3H).
Synthesis of CuEClN
Copper(II) acetate (0.44 g, 2.21 mmol, 1 eq) dissolved in 20 mL of methanol/water (1:1) was added drop-wise over 15 min to EClN (1.0 g, 4.44 mmol, 2 eq). The mixture was refluxed for 4 h. The black precipitate was collected by filtration, washed with water and methanol, and dried under vacuum. Yield: 1.05 g, 47.7 %; m.p. 230 °C; soluble in DMF and DMSO. UV-Vis (DMF, 0.1 mM): λ_max / nm (ε) = 279 (11 030), 355 (6 110), 374 (3 001); at 1 mM: 430 (2 112), 567 (1 184). FT-IR: 3045–3030 ν(=C–H); 2981–2928 ν(C–H); 1733 ν(C=O); 1695 ν(C=N); 1646–1493 ν(C=C); 1200–1043 ν(C–O); 696–509 ν(Cu–O), ν(Cu–N).
Synthesis of CuEClN-py
Pyridine (1.1 mL, 0.0129 mol, 20 eq) was added to CuEClN (0.35 g, 0.63 mmol, 1 eq) in 3 mL of DMF. The mixture was stirred at room temperature for 48 h. The black precipitate was filtered, washed with DCM, methanol and ethanol, and dried under vacuum. Yield: 0.35 g, 30 %; m.p. 280 °C (dec.). UV-Vis (DMSO, 0.04 mM): λ_max / nm (ε) = 273 (11 702), 392 (4 852); at 0.1 mM: 266 (97 050), 391 (51 100), 866 (37). FT-IR: 3045 ν(=C–H); 2980–2855 ν(C–H); 1734 ν(C=O); 1695 ν(C=N); 1647–1493 ν(C=C); 1200–1043 ν(C–O); 696–506 ν(Cu–O), ν(Cu–N).
Synthesis of CuEClN-bpy
4,4ʹ-Bipyridine (0.30 g, 1.9 mmol, 3 eq) was added to CuEClN (0.35 g, 0.74 mmol, 1 eq) in 3 mL of DMF. The mixture was stirred at room temperature for 48 h. The black precipitate was collected, washed with DCM and methanol, and dried under vacuum. Yield: 0.30 g, 50 %; m.p. 292 °C (dec.). UV-Vis (DMF, 0.04 mM): λ_max / nm (ε) = 272 (24 780), 362 (7 225); at 1 mM: 463 (2 301), 557 (1 382). FT-IR: 3063 ν(=C–H); 2980–2933 ν(C–H); 1665 ν(C=N); 1547–1496 ν(C=C); 1226–1027 ν(C–O); 760–511 ν(Cu–O), ν(Cu–N).
Synthesis of CuEClN-C₁V⁺.PF₆⁻
C₁V⁺.PF₆⁻ (0.74 g, 3 eq) was added to CuEClN (0.40 g, 0.74 mmol, 1 eq) in 3 mL of DMF and stirred at room temperature for 30 days. The black precipitate was collected, washed with DCM, methanol and ethanol, and dried under vacuum. Yield: 0.40 g, 50 %; m.p. 250 °C. UV-Vis (DMF, 0.1 mM): λ_max / nm (ε) = 280 (12 210), 359 (2 221), 380 (1 711); at 1 mM: 423 (1 561), 550 (1 101). FT-IR: 3041 ν(=C–H); 2986–2828 ν(C–H); 1654 ν(C=N); 1617–1497 ν(C=C); 1224 ν(C–O); 716–495 ν(Cu–O), ν(Cu–N); the typical ν(P–F) bands of PF₆⁻ counter-ions are observed below 850 cm⁻¹.
Synthesis of CuEClN-V₂²⁺.2PF₆⁻
V₂²⁺.2PF₆⁻ (1.5 g, 1.9 mmol, 3 eq) was added to CuEClN (0.40 g, 0.74 mmol, 1 eq) in 3 mL of DMF and stirred at room temperature for 30 days. The black precipitate was filtered, washed with DCM, methanol and ethanol, and dried under vacuum. Yield: 0.40 g, 38 %; m.p. 235 °C (dec.). UV-Vis (DMF, 0.1 mM): λ_max / nm (ε) = 300 (22 140), 359 (7 514), 398 (4 891); at 1 mM: 435 (2 181), 544 (1 258). FT-IR: 3135–3060 ν(=C–H); 2993–2930 ν(C–H); 1645 ν(C=N); 1603–1495 ν(C=C); 1222 ν(C–O); 779–505 ν(Cu–O), ν(Cu–N).
Activation of zinc powder
Commercial zinc powder (6 g) was stirred for 20 min in 10 mL of 10 % aqueous HCl until vigorous H₂ evolution ceased and the metal surface became bright. The activated metal was filtered as quickly as possible, washed with water, acetone and diethyl ether, and stored under vacuum in a tightly closed black container [18].
RESULTS AND DISCUSSION
FT-IR spectrometry
The free ligand EClN exhibits diagnostic bands at 1733 cm⁻¹ [ν(C=O), ester], 1696 cm⁻¹ [ν(C=N), imine] and 1220–1027 cm⁻¹ [ν(C–O)] (Fig. 1a). Upon coordination to Cu(II) in CuEClN, ν(C=N) shifts to 1695 cm⁻¹ and the ester ν(C=O) is markedly weakened, indicating tautomerization toward the enolate form and chelation through the imine N and the enolate O atoms [12–14] (Fig. 1b). The new low-frequency bands at 696–509 cm⁻¹ are assigned to ν(Cu–N) and ν(Cu–O). The four adducts retain the equatorial signature of CuEClN but display systematic shifts of ν(C=N) on axial coordination (1665 cm⁻¹ in CuEClN-bpy; 1654 cm⁻¹ in CuEClN-C₁V⁺.PF₆⁻; 1645 cm⁻¹ in CuEClN-V₂²⁺.2PF₆⁻), consistent with a fifth donor occupying the apical position of the square pyramid (Fig. 1c–f). The PF₆⁻ counter-ion of viologen-containing adducts is identified by the strong ν(P–F) absorption near 840 cm⁻¹.
Nanocrystalline structural analysis (XRD)
The powder XRD patterns of EClN, CuEClN and the four adducts displayed sharp Bragg reflections in the range 5–80° (2θ) (Fig. 2), confirming that all the prepared compounds are crystalline solids. The dominant diffraction maxima (2θ) are summarised in Table 1.
The shift and the change of relative intensity of the Bragg reflections on going from EClN to CuEClN and then to the adducts unambiguously confirm the formation of a new crystalline phase upon both equatorial chelation by Cu(II) and axial coordination by the auxiliary donor.
Crystallite size from the Scherrer model
The volume-weighted average crystallite size (D) was extracted from each individual reflection through the Scherrer–Debye expression (Eq. 1):
D = Kλ / (β cosθ) (1)
in which K = 0.94 is the shape factor, λ = 0.15405 nm is the Cu Kα wavelength, β is the line full-width at half-maximum (in radians) and θ is the Bragg angle [19,20]. Mean values are reported in Table 2 (column D_Sch). All compounds fall well within the nanocrystalline regime: D_Sch is comprised between ≈ 6 nm (CuEClN-py) and ≈ 45 nm (CuEClN), which is two orders of magnitude smaller than the wavelength of visible light and accounts for the broad XRD peaks observed.
Williamson–Hall analysis: combined size and microstrain
Because the Scherrer model attributes peak broadening exclusively to size and ignores micro-strain, it tends to over-estimate D in strained lattices. The Williamson–Hall (W–H) model overcomes this limitation by separating the two contributions through Eq. 2:
β cosθ = Kλ / D + 4ε sinθ (2)
where ε represents the dimensionless microstrain. A plot of β cosθ versus 4 sinθ affords ε from the slope and D_W–H from the intercept Kλ / D_W–H [20,21]. The W–H plots of the present chlorinated series are gathered in Fig. 3, and the fitted parameters are summarized in Table 2.
Three structure–property correlations emerge from Table 2 and Fig. 3. (i) The free ligand EClN and the parent complex CuEClN show D_W–H ≥ D_Sch and a small absolute strain, consistent with an efficient packing of small, neutral and approximately planar molecules; the strain is formally compressive, i.e. the lattice is compacted by short Cl‧‧‧H and Cl‧‧‧π contacts that the chlorinated chain is able to develop in the solid state. (ii) Axial coordination of a fifth donor at Cu(II) systematically reduces D and switches the strain from compressive to tensile (D_W–H > D_Sch), because the bulky auxiliary ligand swells the unit cell. The effect is largest for the rigid pyridine ring, which forces π–π stacking and lowers D_Sch to only ≈ 8 nm. (iii) The two viologen-containing adducts — although bigger — do not show the largest D drop, because the propylene-bridged bis-viologen of CuEClN-V₂²⁺.2PF₆⁻ has a flexible methylene linker that absorbs part of the lattice mismatch, while the PF₆⁻ counter-ions act as soft buffers between the cationic units; nevertheless, this complex displays the highest absolute strain of the series (ε = 1.56 × 10⁻³) because it brings together the largest steric volume and the highest charge.
A direct comparison with the non-chlorinated analogues (EN-based complexes) reveals that chlorination produces, in most cases, a modest increase of D_Sch but a sharper increase of ε, owing to enhanced anisotropic Cl-mediated contacts. This trend is in line with the observation that halogen substituents in coordination polymers can act simultaneously as crystal-engineering tools and as sources of nano-strain.
FE-SEM morphology at the nano/micro scale
Field-emission scanning electron microscopy was used as an independent probe of the size and morphology trends predicted by the W–H analysis (Fig. 4). EClN appears as plate-like or shard-like fragments with rough surfaces and dispersed sub-50 µm features (Fig. 4a); the SEM background reveals voids that signal a low compactness, in agreement with the small absolute strain. After complexation, CuEClN displays a more uniform texture in which smaller secondary domains aggregate into larger blocks (Fig. 4b). The pyridine adduct CuEClN-py forms blocky aggregates of ≈ 10–30 µm built from much smaller (sub-10 µm) secondary particles (Fig. 4c), faithfully matching the bimodal D_Sch/D_W–H ratio noted by W–H. CuEClN-bpy is more dispersed and shows larger plate-like grains (Fig. 4d), indicating that the longer 4,4ʹ-bipyridine spacer favours growth in one direction. CuEClN-C₁V⁺.PF₆⁻ displays dense aggregates with little void space (Fig. 4e), in line with the strong electrostatic interactions between the cationic viologen units and the PF₆⁻ counter-ions [22]. By contrast, CuEClN-V₂²⁺.2PF₆⁻ is finer and more uniformly dispersed (Fig. 4f); the dicationic V₂²⁺ unit increases inter-particle electrostatic repulsion, reduces aggregation and produces a powder of sub-micron crystallites — again in agreement with the highest microstrain (ε = 1.56 × 10⁻³) measured by W–H. The qualitative FE-SEM trend is therefore fully consistent with the quantitative XRD/W–H data.
Thermogravimetric analysis
TG/DTA traces of EClN and its Cu(II) complexes were recorded at 10 °C min⁻¹ between room temperature and 600–800 °C in air or argon. The free ligand EClN decomposes in a single, sharp step that is essentially complete by 380 °C, with a residual mass close to zero — consistent with the absence of an inorganic core. CuEClN and the four adducts decompose in two well-separated steps: a first step (~200–300 °C) corresponds to the loss of the axial ligand and of part of the equatorial Schiff base, and a second step (~400–600 °C) to the carbonisation of the residual organics, leaving a stable copper oxide residue. Treating each step as a first-order process and applying the Coats–Redfern equation allowed us to extract the rate constants k₁, the half-lives t₁₂ and the activation energies E_a, as well as the thermodynamic parameters ΔH*, ΔS* and ΔG*. All the decompositions are non-spontaneous (ΔG* > 0), endothermic (ΔH* > 0) and entropically disfavoured (ΔS* < 0). The thermal stability sequence (according to E_a) follows the rigidity of the axial donor: CuEClN < CuEClN-V₂²⁺.2PF₆⁻ < CuEClN-bpy ≈ CuEClN-C₁V⁺.PF₆⁻ < CuEClN-py, indicating that planar, well-packed pyridine adducts are more thermally robust than the bulkier viologen ones — in line with their lower microstrain.
UV-Visible absorption and coordination geometry
The free ligand EClN displays two intense absorption bands near 303 nm (π–π*) and 427 nm (n–π*) in DMF. CuEClN shows two equatorial π–π* bands at 279 and 355 nm, an MLCT shoulder at 374 nm, and — at 1 mM — a broad, weak d–d transition centred at 567 nm; this is the diagnostic feature of a square-planar N₂O₂ chromophore around Cu(II). After axial coordination by py, bpy, C₁V⁺.PF₆⁻ or V₂²⁺.2PF₆⁻, the d–d transition broadens significantly and shifts: in DMF, CuEClN-bpy displays a clear d–d band at 557 nm, CuEClN-C₁V⁺.PF₆⁻ at 550 nm and CuEClN-V₂²⁺.2PF₆⁻ at 544 nm, whereas CuEClN-py in DMSO displays a weak band at 866 nm consistent with axial dz² perturbation. The crystal-field splitting pattern of square-pyramidal Cu(II) (dxz, dyz > dx²–y² > dz² > dxy) accounts for these observations and supports the assignment of a five-coordinate geometry for every adduct, in agreement with the FT-IR and XRD data.
Redox-triggered π-dimerization: molecular switching
Chemical reduction by activated zinc
In a typical experiment, a deoxygenated DMF solution of CuEClN-C₁V⁺.PF₆⁻ (0.2 mM) was treated under argon with a small excess of activated zinc powder. A deep colour developed within minutes; UV-Vis monitoring revealed two new bands at 380 and 554 nm, which are the unambiguous signatures of an inter-molecular π-dimer (CuEClNC₁V•)₂ [23,24]. At lower concentration (0.1 mM) the band at 380 nm dominates while the 554 nm band weakens, indicating a concentration-dependent monomer/dimer equilibrium. Exposure of the reduced solution to air for four days produces the bands at 412 and 550 nm, attributed to the partially re-oxidised viologen radical CuEClNC₁V• in equilibrium with residual π-dimer.
Reduction of CuEClN-V₂²⁺.2PF₆⁻ under the same conditions delivers a different scenario. Both viologen units are reduced to their radical-cations and the propylene tether enforces an intramolecular π-dimer (CuEClNV₂) within a single molecule, signalled by the absorption bands at 398 nm (residual radicals) and 560 nm (intramolecular π-dimer). The on-/off- character of the switch is again confirmed by air re-oxidation, which restores the absorption profile of the parent CuEClN-V₂²⁺.2PF₆⁻. The two redox-triggered switches are therefore complementary: CuEClN-C₁V⁺.PF₆⁻ operates as a bimolecular “clamp” between two complex units while CuEClN-V₂²⁺.2PF₆⁻ operates as a unimolecular “fold-and-unfold” device.
Cyclic voltammetry
Cyclic voltammograms in DMF + 0.1 M TBAP confirm the spectroscopic picture and supply quantitative redox data. Free C₁V⁺.PF₆⁻ shows two consecutive one-electron reductions: the first irreversible at −0.93 V vs. Ag and the second quasi-reversible at E₁₂ = −0.97 V (ΔEp = 135 mV; ipa/ipc = 0.96 at 0.3 V s⁻¹), corresponding to V⁺ / V• and V• / V respectively. Upon coordination to CuEClN, the first reduction shifts anodically (E_pc1 = −0.86 V), proving that the cationic viologen is even easier to reduce when bound to the electron-withdrawing copper environment, and that the formation of the inter-molecular π-dimer (CuEClNC₁V•)₂ is thermodynamically favourable [25]. Free V₂²⁺.2PF₆⁻ exhibits two reductions at −0.50 V (radical formation followed by intramolecular π-dimerisation) and −0.69 V (further reduction to the neutral V₂ species, with break-up of the π-dimer). Coordination to CuEClN cathodically shifts the first reduction to E_pc1 ≈ −0.86 V and the second to E_pc2 = −0.86 V, confirming the formation of an intramolecular π-dimer within the structure of CuEClN-V₂²⁺.2PF₆⁻. A coordinated bpy reduction at −1.15 V is also clearly distinguished in CuEClN-bpy, in agreement with the expected cathodic shift relative to the free 4,4ʹ-bipyridine (−1.09 V).
Taken together, the chemical and electrochemical experiments constitute an unambiguous demonstration that the present nanocrystalline Cu(II) complexes operate as molecular switches: the redox state of the axial viologen is the input, the formation/dissociation of the π-dimer is the molecular event, and the absorption fingerprint at ≈ 380 and ≈ 554–560 nm is the readable output.
CONCLUSION
A new chlorinated Schiff-base ligand, EClN, its parent copper(II) complex CuEClN, and four axial adducts CuEClN-L (L = py, bpy, C₁V⁺.PF₆⁻, V₂²⁺.2PF₆⁻) were synthesised in good yields and fully characterised. Powder X-ray diffraction together with the Williamson–Hall model demonstrated that the whole series belongs to the nanocrystalline regime, with average crystallite sizes between ≈ 6 and ≈ 81 nm and microstrains comprised between 0.2 × 10⁻³ (parent ligand) and 1.56 × 10⁻³ (bis-viologen adduct). Axial coordination systematically reduces D and switches the strain from compressive (small molecules) to tensile (bulky charged adducts), and FE-SEM imaging confirmed the trend at the nano/micro scale. UV-Vis and FT-IR spectroscopies established the square-pyramidal CuN₂O₂L geometry of every adduct, and TGA showed that thermal stability is governed by the rigidity of the axial donor. Most importantly, chemical reduction by activated zinc and electrochemical reduction by cyclic voltammetry produced, respectively, the inter-molecular π-dimer (CuEClNC₁V•)₂ and the intra-molecular π-dimer of CuEClNV₂, with reversible reformation of the precursor under air. The chlorinated nanocrystalline copper complexes here introduced therefore behave as redox-triggered molecular switches whose nano-structure can be tuned through the choice of axial donor — a feature of clear interest for molecular electronics, redox-responsive smart materials and electrochromic devices.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the Department of Chemistry, College of Science, University of Thi-Qar (Iraq) for laboratory facilities, and the University of Tehran (Iran) and the College of Education for Pure Sciences – University of Basrah for instrumental support (LC-MS, TGA, XRD, NMR, FE-SEM).
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.
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