Kinetics of underpotential deposition and nucleation of copper on the Pt(111) face in the presence of acetonitrile

The kinetics of underpotential deposition, three-dimensional nucleation, and growth of copper deposits at cathodic overpotentials on a Pt(111) electrode in solutions containing 0.5 M H₂SO₄, 10 mM CuSO₄, and 0–200 mM acetonitrile (AcN) is studied by the cyclic voltammetry, potentiostatic current transients, and scanning probe microscopy methods. At low volume concentrations of acetonitrile ([AcN] ≤ 4 mM), adsorbed acetonitrile molecules accelerate the formation of a co-adsorption lattice of copper adatoms with anions due to local electrostatic effects at the charged interface. At higher concentrations, the underpotential deposition process is hampered, but the desorption of copper adatoms occurs at potentials more positive than those at low acetonitrile concentrations. This effect is attributed to a stabilizing action of acetonitrile molecules situated on the layer of copper adatoms and, in part, on platinum. At [AcN] = 0.4–40 mM, adsorbed acetonitrile molecules accelerate the growth of the bulk copper deposit, but the nucleation stage is hindered. The dependence of the copper amount on the deposition potential at [AcN] = 40 mM exhibits a maximum at 0.15–0.17 V. This effect was previously observed in weakly acid solutions (pH 1.7–3.0) containing no acetonitrile. The maximum rate of the deposit growth corresponds to an optimum number of crystallites (which is not too great) and an optimum distance between the growing centers in conditions of mixed kinetics “diffusion + electron transfer.” A substantial number of complexes Cu(I)-AcN forms at high acetonitrile concentrations.     

Initial stages of copper electrocrystallization on polycrystalline platinum and glassy carbon in the presence of acetonitrile

The kinetics of formation of copper adlayer, three-dimensional nucleation, and the deposit growth on polycrystalline platinum and glassy carbon in the 0.5 M H₂SO₄ + 10 mM CuSO₄ + (0–2) M acetonitrile (AcN) solutions at the cathodic overvoltages is studied using the methods of cyclic voltammetry and potentiostatic current transients on a ring-disc electrode. At [AcN] = 2 M, the process of formation of copper adatoms on platinum is significantly retarded. In the solutions with high contents of AcN, the processes of Cu⁺ ion production, the formation of their complexes with acetonitrile, hydrogen evolution, copper nucleation, and the deposit growth proceed in parallel. The contribution of any process to the overall current depends on the amount of adsorbed AcN at the surface of substrate and copper deposit and on the electrode potential. At [AcN] = 2 M, an increase in the cathodic overvoltage to 0.32 V leads to an abnormal increase in the current of Cu⁺ ion production on platinum, which is caused by insufficiently rapid formation of copper atoms in the reduction of Cu⁺(AcN) _x complexes.     

Kinetics of copper UPD on stepped platinum single crystals in the presence of acetonitrile

The kinetics of copper underpotential deposition on stepped Pt(h k l) electrodes with controlled width of (1 1 1) terraces in acidic solutions of copper sulfate with 0–200 mM of acetonitrile (AcN) has been studied by means of cyclic voltammetry. In the presence of AcN Cu UPD process is hindered both at (1 0 0) steps and (1 1 1) terraces of Pt(17 15 15) and Pt(7 5 5) faces due to blocking of the electrode surface with organic molecules, strongly adsorbed at the steps and nearby ones. The decoration of (1 1 0) steps with copper adatoms is slightly accelerated for Pt(7 7 5) electrode in the solution with 0.04 mM AcN. Increase in AcN concentration leads to inhibition of the UPD process. The difference in behavior of the stepped platinum electrodes is controlled by competitive adsorption of AcN, (bi)sulfate and Cu atoms at the step sites. AcN adsorption at (1 0 0) steps is stronger as compared with (1 1 0) ones.     

Stability of Ultradisperse Copper in a Sulfo Cation Exchanger Matrix

The recrystallization of ultradisperse copper chemically deposited onto a sulfo cation exchanger matrix was studied by the potentiometric method. The stationary value of the electrode potential of the copper-sulfo cation exchanger composite was established during a long period of time, which depended on the ionic form of the composite (H⁺, Cu²⁺, or Na⁺), solution composition (CuSO₄, H₂SO₄, and Na₂SO₄), and solution concentration. Recrystallization was favored by copper(II) counterions, which entered the composite as a result of ion exchange, nonexchange absorption of copper sulfate, or preliminary composite transformation into the Cu²⁺ form. In the quasi-equilibrium state, the concentration of copper(II) counterions was maintained at a high level by the Donnan interfacial potential. At all the copper(II) sulfate concentrations used, the potential of the Cu²⁺/Cu ion—metal pair in the ion-exchange matrix remained at virtually the same level, which was indicative of the stable state of copper particles. In the absence of an external source of copper ions, recrystallization was significantly hindered; therefore, the potential exhibited only a slight drift. Copper ions formed in the solution of small crystals were localized in the vicinity of ionogenic matrix centers, which decreased the mobility of these particles as counterions; therefore, the dispersity of particles remained unchanged.     

Bis(homoleptische) vs. heteroleptische Kupfer(I)-Komplexe: Elektrosynthese,Spektroskopie und Kristallstruktur von {[Cu(BIK)2]+}2{[Cu4(SR)6]2−} · 3(CH3CN) · (RSH); BIK = Bis(N-methylimidazol-2-yl)keton,R = o-Tolyl

Bis(homoleptic) vs. Heteroleptic Copper(I) Complexes: Electrosynthesis, Spectroscopy, and Crystal Structure of {[Cu(BIK)₂]⁺}₂{[Cu₄(SR)₆]^2?} · 3(CH₃CN) · (RSH); BIK = Bis(2-methylimidazol-2-yl)ketone, R = o-Tolyl Anodic oxidation of copper in acetonitrile/2 mM tetrabutylammonium perchlorate and in the presence of bis(N-methylimidazol-2-yl)ketone (BIK) and excess o-thiocresol RSH yields the title compound as main product. Whereas the dianionic cluster [Cu₄(SR)₆]^2? is similar to previously reported such species with R = phenyl or methyl, the purple cations [Cu(BIK)₂]⁺ exhibit spectroscopic and structural effects of π back bonding between electron-rich Cu¹ and the π acceptor ligand BIK. In contrast to the formally related [Zn(BIK)₂]²⁺, the copper(I) complex cations exhibit distorted tetrahedral structures with almost coplanar BIK chelate arrangements which ensures maximum metal-ligand π interaction.     

Reduction of copper(II) complexes by electron capture in an electrospray ionization source

The relative proportion of 1:1 Cu(I)– and Cu(II)–peptide complexes PeptCu(I)⁺ and [Pept?H+Cu(II)]⁺ yielded by electrospray ionization of copper sulfate and GlyHisLys solutions in water/methanol was examined under different source conditions. Two factors leading to an increase in Cu(I) complex ratio were found. (1) Increase of nozzle–skimmer voltages caused collision-induced dissociation of Cu(II) complexes, and most probably favor ligand-to-metal electron transfers that result in the decoordination of oxydated ligands to form PeptCu⁺. (2) Independent of these “innersphere” processes that involve only electron exchange inside the coordination sphere around the metal cation, an increase in source voltages with a concomitant increase of current and, supposedly, electron counterflow between the counterelectrode and the capillary caused an increase in PeptCu⁺ relative proportion. The hypothesis that an “outersphere” electron capture might happen in these conditions was verified by using discharge supressing SF₆ gas as nebulizing gas. The electronegative gas reduced the current brought on by high voltages and inhibited the PeptCu⁺ increase phenomenon.     

Cu + Au alloy particles formed in the underpotential deposition region of copper in acid solutions

Cu + Au alloy particles electrodeposited on an amorphous carbon electrode at the underpotential region of Cu in both perchloric acid and sulfuric acid solutions were investigated by means of transmission electron microscopy. The fraction of Cu in the Cu + Au alloy particles grown in both acid solutions with a concentration of 1 mM Au ion increased while the underpotential deposition (UPD) potential was decreased. However, it was independent of the concentration of Cu ion in solution. It is inferred that the composition of the Cu + Au alloy particles is dependent on the UPD potential. The fraction of Cu in the Cu + Au alloy particles grown at around the reversible Nernst potential of Cu in 0.1 mM HAuCl₄ + 50 mM Cu(ClO₄)₂ containing perchloric acid solution was 505. This result suggests a layer-by-layer formation of the Cu + Au alloy particles. The fraction of Cu in the Cu + Au alloy particles formed in the presence of sulfate was lower than that in the perchloric acid solution as the UPD potential and the concentration of Cu ion were the same. This is attributed to an influence of coadsorbed sulfate ions.     

Electroreduction of carbon monoxide on palladium electrodeposits in solutions containing copper ions

It is shown that the electroreduction of CO proceeds on electrolytic deposits of palladium (edPd) in 0.5 M H₂SO₄ + (1–5) mM CuSO₄ + CO(sat) solutions at the potentials more positive than the Cu²⁺/Cu equilibrium potential. Among the CO reduction products, methanol and formaldehyde are identified. The current efficiency with respect to CH₃OH exceeds 75% on edPd formed in 1% PdCl₂+0.5 M H₂SO₄ solutions. In addition, Cu⁺ ions, which probably form complexes with CO, are detected in the solution and are assumed to play the role of intermediate species in the mediator catalysis along with copper adatoms.     

A new copper containing MALDI matrix that yields high abundances of [Peptide + Cu]+ ions

The dinuclear copper complex (α-cyano-4-hydroxycinnamic acid (CHCA) copper salt (CHCA)₄Cu₂), synthesized by reacting CHCA with copper oxide (CuO), yields increased abundances of [M + xCu − (x−1)H]⁺ (x = 1–6) ions when used as a matrix for matrix-assisted laser desorption ionization (355 nm Nd:YAG laser). The yield of [M + xCu − (x−1)H]⁺ (x = 1∼6) ion is much greater than that obtained by mixing peptides with copper salts or directly depositing peptides onto oxidized copper surfaces. The increased ion yields for [M + xCu − (x−1)H]⁺ facilitate studies of biologically important copper binding peptides. For example, using this matrix we have investigated site-specific copper binding of several peptides using fragmentation chemistry of [M + Cu]⁺ and [M + 2Cu − H]⁺ ions. The fragmentation studies reveal interesting insight on Cu binding preferences for basic amino acids. Most notable is the fact that the binding of a single Cu⁺ ion and two Cu⁺ ions are quite different, and these differences are explained in terms of intramolecular interactions of the peptide-Cu ionic complex.     

Effect of copper precursors on the catalytic activity of Cu/ZSM-5 catalysts for selective catalytic reduction of NO by NH<Subscript>3</Subscript>

The Cu/ZSM-5 catalysts prepared by different copper precursors were used for the selective catalytic reduction (SCR) of NO _x with NH₃. The Cu/ZSM-5 catalyst prepared by the copper nitrate (Cu/ZSM-5-N) presented the best performance among the Cu/ZSM-5 catalysts and showed above 90 % NO _x conversion at 225–405 °C. The average particle size of CuO was 5.82, 9.20, and 11.01 nm over Cu/ZSM-5-N, Cu/ZSM-5-S (prepared by copper sulfate), and Cu/ZSM-5-C (prepared by copper chloride), respectively. The Cu/ZSM-5-N catalyst showed the highly dispersed copper species, the strong surface acidity, and the excellent redox ability compared with the Cu/ZSM-5-C and Cu/ZSM-5-S catalysts. The Cu⁺ and Cu²⁺ existed in the Cu/ZSM-5 catalysts and the abundant Cu⁺ over Cu/ZSM-5-N might be responsible for the superior SCR activity.     

Dioxygen Reduction in Acetonitrile with Copper Pyridylalkylamine Complexes: The Influence of Acid Strength on the Catalytic Performance

The pyridylalkylamine copper complex [Cu(tmpa)(L)]²⁺ has previously been proposed to reduce dioxygen via a dinuclear resting state, based on experiments in organic aprotic solvents using chemical reductants. Conversely, a mononuclear reaction mechanism was observed under electrochemical conditions in a neutral aqueous solution. We have investigated the electrochemical oxygen and hydrogen peroxide reduction reaction catalyzed by [Cu(tmpa)(L)]²⁺ in acetonitrile, using several different acids over a range of pK_a. We demonstrate that strong acids lead to the loss of redox reversibility and to the destabilization of the copper complex under non-catalytic conditions. Under milder conditions, the electrochemical oxygen reduction reaction (ORR) was shown to proceed via a mononuclear catalytic intermediate, similar to what we have previously observed in water. However, in acetonitrile the catalytic rate constants of the ORR are dramatically lower by a factor 10⁵, which is caused by the unfavorable equilibrium of formation of [Cu^II(O₂⋅⁻)(tmpa)]⁺ in acetonitrile. This results in higher catalytic rates for the reduction of hydrogen peroxide than for the ORR.     

Study of copper electrodeposition from acidic sulfate and perchlorate electrolytes using faradaic impedance spectroscopy and quartz microbalance methods

Copper electrodeposition from acidic sulfate and perchlorate electrolytes is studied. Some measurements are performed with addition of gelatine as a surface active agent. In the course of microgravimetric studies, decrease of the derivative of the electrode mass variation by the consumed charge is found, as compared to the value corresponding to the current efficiency of 100%. The latter is in part related to the effect of the double layer structure on the rate of the consecutive stages of copper recharge (Cu²⁺ + e → Cu⁺) and deposition (Cu⁺ + e → Cu). This effect is most pronounced in the case of solutions containing surface active agents that cause hyperpolarization and extension of the monovalent copper stability range as a result of their adsorption on the electrode surface. The faradaic impedance spectra obtained in sulfate and perchlorate electrolytes evidence at least the difference in the rate constants of recharge and copper deposition in these electrolytes. In both cases, the recharge rate constant is considerably lower than the deposition rate constant. The difference between these constants decreases noticeably at the addition of surface active agents.     

Binuclear copper complexes with non-steroidal anti-inflammatory drugs as studied by electrospray ionization mass spectrometry

The solutions containing one of the copper salts (CuCl₂, Cu(ClO₄)₂, Cu(NO₃)₂, and CuSO₄) and one of the non-steroidal anti-inflammatory drugs (NSAIDs, ibuprofen, ketoprofen or naproxen) were analyzed by electrospray ionization mass spectrometry. Three of the salts, namely CuCl₂, Cu(ClO₄)₂ and Cu(NO₃)₂, yielded binuclear complexes of drug:metal stoichiometry 1:2. Existence of the complexes of such stoichiometry has not been earlier observed. For copper(II) chloride the complexes (ions of the type [M-HCOOH+Cu₂Cl]⁺ and [M+Cu₂Cl]⁺, M stands for the drug molecule) were formed in the gas phase. When copper(II) perchlorate or copper(II) nitrate was used, the observed binuclear copper complexes (ions of the type [M-H+Cu₂(ClO₄)₂+CH₃OH]⁺, [M-H+Cu₂(ClO₄)₂]⁺ and [M-H+Cu₂(NO₃)₂+CH₃OH]⁺, [M-H+Cu₂(NO₃)₂]⁺) were observed at low cone voltage, thus these complexes must have already existed in the solution analysed. Therefore, such complexes may also exist under physiological conditions.      

Examining the impact of ancillary ligand basicity on copper(I)–ethylene binding interactions: a DFT study

A theoretical investigation at the density functional theory level (B3LYP) has been conducted to elucidate the impact of ligand basicity on the binding interactions between ethylene and copper(I) ions in [Cu(?? ²-C₂H₄)]⁺ and a series of [Cu(L)(?? ²-C₂H₄)]⁺ complexes, where L?=?substituted 1,10-phenanthroline ligands. Molecular orbital analysis shows that binding in [Cu(?? ²-C₂H₄)]⁺ primarily involves interaction between the filled ethylene ??-bonding orbital and the empty Cu(4s) and Cu(4p) orbitals, with less interaction observed between the low energy Cu(3d) orbitals and the empty ethylene ??*-orbital. The presence of electron-donating ligands in the [Cu(L)(?? ²-C₂H₄)]⁺ complexes destabilizes the predominantly Cu(3d)-character filled frontier orbital of the [Cu(L)]⁺ fragment, promoting better overlap with the vacant ethylene ??*-orbital and increasing Cu????ethylene ??-backbonding. Moreover, the energy of the filled [Cu(L)]⁺ frontier orbital and mixing with the ethylene ??*-orbital increase with increasing pK _a of the 1,10-phenanthroline ligand. Natural bond orbital analysis reveals an increase in Cu????ethylene electron donation with addition of ligands to [Cu(?? ²-C₂H₄)]⁺ and an increase in backbonding with increasing ligand pK _a in the [Cu(L)(?? ²-C₂H₄)]⁺ complexes. Energy decomposition analysis (ALMO-EDA) calculations show that, while Cu????ethylene charge transfer (CT) increases with more basic ligands, ethylene????Cu CT and non-CT frozen density and polarization effects become less favorable, yielding little change in copper(I)?Cethylene binding energy with ligand pK _a. ALMO-EDA calculations on related [Cu(L)(NCCH₃)]⁺ complexes and calculated free energy changes for the displacement of acetonitrile by ethylene reveal a direct correlation between increasing ligand pK _a and the favorability of ethylene binding, consistent with experimental observations.     

Redox reactions of uranium hexafluoride. Comparison with phosphorus pentafluoride and preparation of copper(I) hexafluorouranate(V) [1]

Molecular iodine is oxidised by phosphorus pentafluoride in iodine pentafluoride at room temperature giving I₂⁺, PF₆^?, and PF₃. I₂⁺ is formed from uranium hexafluoride under similar conditions, but further oxidation occurs depending on the reaction stoicheiometry used. In all cases uranium pentafluoride is formed. Copper(II) fluoride reacts with UF₅ in acetonitrile at room temperature to give copper(II) hexafluorouranate(V), which is reduced by copper metal to give the copper(I) salt. The latter compound is formed from UF₆ and Cu metal, via the Cu^II salt, only if a fresh Cu surface is used for the reduction step.     

Zeolite ZSM-5 containing copper ions: The effect of the copper salt anion and NH<Subscript>4</Subscript>OH/Cu<Superscript>2+</Superscript> ratio on the state of the copper ions and on the reactivity of the zeolite in DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO _x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO _x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO _x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).     

Charge storage mechanism of copper hexacyanoferrate nanocubes for supercapacitors

The widely accepted theory concerning the electrochemical energy storage mechanism of copper hexacyanoferrate (CuHCF) for supercapacitors is that CuHCF stores charge by the reversible redox processes of Fe³⁺/Fe²⁺ couple and Cu cations are electrochemically inactive. In this work, CuHCF nanocubes (CuHCF-NC) were synthesized in the presence of potassium citrate and its electrochemical properties were tentatively studied in 1 mol/L Na₂SO₄ aqueous electrolyte. Good supercapacitive performance was exhibited. The combined analyses of cyclic voltammogram (CV) and X-ray photoelectron spectroscopy (XPS) disclosed that the CuHCF nanocubes underwent the redox reactions of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ couples to store charges. The Cu²⁺/Cu⁺ redox couple was activated due to the strong coordination interaction between the carboxylate groups of citrate ions and surface Cu cations.     

Examining the impact of ancillary ligand basicity on copper(I)–ethylene binding interactions: a DFT study

A theoretical investigation at the density functional theory level (B3LYP) has been conducted to elucidate the impact of ligand basicity on the binding interactions between ethylene and copper(I) ions in [Cu(η ²-C₂H₄)]⁺ and a series of [Cu(L)(η ²-C₂H₄)]⁺ complexes, where L = substituted 1,10-phenanthroline ligands. Molecular orbital analysis shows that binding in [Cu(η ²-C₂H₄)]⁺ primarily involves interaction between the filled ethylene π-bonding orbital and the empty Cu(4s) and Cu(4p) orbitals, with less interaction observed between the low energy Cu(3d) orbitals and the empty ethylene π*-orbital. The presence of electron-donating ligands in the [Cu(L)(η ²-C₂H₄)]⁺ complexes destabilizes the predominantly Cu(3d)-character filled frontier orbital of the [Cu(L)]⁺ fragment, promoting better overlap with the vacant ethylene π*-orbital and increasing Cu → ethylene π-backbonding. Moreover, the energy of the filled [Cu(L)]⁺ frontier orbital and mixing with the ethylene π*-orbital increase with increasing pK _a of the 1,10-phenanthroline ligand. Natural bond orbital analysis reveals an increase in Cu → ethylene electron donation with addition of ligands to [Cu(η ²-C₂H₄)]⁺ and an increase in backbonding with increasing ligand pK _a in the [Cu(L)(η ²-C₂H₄)]⁺ complexes. Energy decomposition analysis (ALMO-EDA) calculations show that, while Cu → ethylene charge transfer (CT) increases with more basic ligands, ethylene → Cu CT and non-CT frozen density and polarization effects become less favorable, yielding little change in copper(I)–ethylene binding energy with ligand pK _a. ALMO-EDA calculations on related [Cu(L)(NCCH₃)]⁺ complexes and calculated free energy changes for the displacement of acetonitrile by ethylene reveal a direct correlation between increasing ligand pK _a and the favorability of ethylene binding, consistent with experimental observations.     

Synthesis and Coordination of Tripodal-Containing Copper(I) Complexes

Reaction of copper(I) chloride with 2,2-bis(diphenylphosphinomethyl)-l-phenylthiopropane P₂S produced a dimeric species [(P₂S)CuC1]₂ (2). Treatment of 2 with silver nitrate in acetonitrile gave a hexameric crystalline metal complex {[(P₂S)Cu(CH₃CN)]₆⁺6NO₃} (4), which had a “cyclodextrin-type” structure. A linear polymeric copper complex [(P₂S)Cu(NO₃)]_n was obtained by recrystallization of 4 in chloroform. These complexes were characterized by single crystal analyses, and their coordination behaviors in solution are discussed.     

Synthesis,structure, and antioxidative properties of a copper(II) complex with 1,2-bis(benzimidazol-2-yl)ethane ligand

1,2-Bis(benzimidazol-2-yl)ethane (bbe) and its copper(II) complex, {[Cu(bbe)Br₂]₂}·2DMF ( 1 ), have been synthesized and characterized by elemental analysis, ultraviolet–visible, and infrared spectra. The single crystal structure analysis of 1 shows two crystallographically independent but chemically identical [Cu(bbe)Br₂] molecules. The coordination geometry of the copper atoms may best be described as a distorted tetrahedron (τ₄ = 0.740 for Cu1 and 0.696 for Cu2). The cyclic voltammogram of complex 1 represents quasi-reversible Cu²⁺/Cu⁺ pairs. in vitro antioxidant tests showed that complex 1 has significant antioxidant activity against superoxide and hydroxy radicals. Photoluminescence investigations showed that the fluorescence intensity of complex 1 is significantly weaker than that of the ligand. This may be due to the paramagnetic effect of divalent copper to cause quenching of fluorescence.