Studies on the kinetics and mechanism of dissociation of copper(II) and nickel(II) complexes of the macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene in perchloric acid media

Summary Acid catalysed dissociation of the copper(II) and nickel(II) complexes (ML²⁺ of the quadridentate macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene (L) has been studied spectrophotometrically. Both complexes dissociate quite slowly with the observed pseudo-first order rate constants (k_obs) showing acid dependence; for the nickel(II) complex (k_obs)=k_O+k_H[H⁺], the k_o path is however absent with the copper(II) complex. At 60°C (I=0.1M) the k_H values areca 10^–4 M^–1 s^–1 for both complexes; k _H ^Cu /k _H ^Ni =ca. 3.9, comparable to some other square-planar complexes of these metal ions. The rate difference is primarily due to H values [copper(II) complex, 29.4±0.5 kJ mol^–1; nickel(II) complex, 35.6±1.5 kJ mol^–1] with highly negative S values [for copper(II), –215.5 ±6.1 JK^–1 mol^–1 and for nickel(II), –208.1 ±5.6 JK^–1 mol^–1] which are much higher than the entropy of solvation of Ni²⁺ (ca. –160 JK^–1 mol^–1) and Cu²⁺ (ca. –99 JK^–1 mol^–1) ions; significant solvation of the released metal ions and the ligand is indicated.     

Molecular structures and ESR spectra of copper(ii) complexes with 2-hydroxypropiophenone acyldihydrazones

The dinuclear copper(ii) complexes with 2-hydroxypropiophenone acyldihydrazones (H₄L) having the composition [Cu₂L·mPy], where the L ligand contains the polymethylene chain with different lengths (from two to five units), were synthesized and studied. The crystal and molecular structures of the 2-hydroxypropiophenone adipoylhydrazone complex [Cu₂L·4Py]·Py were established by X-ray diffraction analysis. Copper atoms are 8.212 distant from each other, and their nearest environment has the tetragonal pyramidal geometry. The ESR spectra of solutions of the complexes based on acyldihydrazones of succinic, glutaric, and adipic acids contain seven HFS lines with the constant 40·10^–4 cm^–1 from two equivalent copper atoms. The spectra were interpreted as a result of the spin-spin exchange interaction of two unpaired electrons. An increase in the polymethylene chain length to five units prevents exchange interactions. The ESR spectrum of the complex with acyldihydrazone of pimelic acid contains a signal of four HFS lines with a _Cu = 73.4·10^–4 cm^–1, which is typical of mononuclear copper(ii) complexes.     

Synthesis and magnetic properties of μ-oxalato-bridged Cu2 IIFeIII-type heterotrinuclear complexes

Three new -oxalato-bridged heterotrinuclear copper(II)–iron(III)–copper(II) complexes have been synthesized and identified: [Cu₂Fe(ox)₃L₂]ClO₄ [L = 5-nitro-1,10-phenanthroline (NO₂phen); 2,9-dimethyl-1,10-phenanthroline (Me₂phen) or 2,2-bipyridine (bpy), respectively]; ox = the oxalato dianions. Based on elemental analyses, molar conductivity and magnetic moment (at room-temperature) measurements, i.r. and electronic spectral studies, extended ox-bridged structures consisting of two copper(II) and an iron(III) ions, in which the central iron(III) ion has an octahedral environment and the end-capped two copper(II) ions a square-planar environment, are proposed for these complexes. The [Cu₂Fe(ox)₃(Me₂phen)₂]ClO₄ (1) and [Cu₂Fe(ox)₃(bpy)₂]ClO₄ (2) complexes were characterized further by variable-temperature magnetic susceptibility (4.2–300 K) measurements and the observed data were simulated by the equation based on the spin Hamiltonian operator, = –2J₁ · ₂, giving the exchange integrals J = –12.85 cm^–1 for (1) and J = –11.28 cm^–1 for (2). The results indicate the presence of an antiferromagnetic spin-exchange interaction between the copper(II) and iron(III) ions through the oxalato-bridge in both complexes (1) and (2).     

Copper(II)–1,2-bis(thiocarbamoyl)hydrazine and copper(II)–(1-carbamoyl-2-thiocarbamoyl)hydrazine complexing in copper(II)hexacyanoferrate(II) gelatin-immobilized matrix systems

The complex formation that occurs in gelatin-immobilized copper(II)hexacyanoferrate(II) matrices upon contact with aqueous alkaline (pH 12.0) solutions of 1,2-bis(thiocarbamoyl)hydrazine, H₂NC(S)NHNHC(S)NH₂ and 1-carbamoyl-2-(thiocarbamoyl)hydrazine, H₂NC(O)NHNHC(S)NH₂ has been studied. The reaction of each of these ligands with copper(II) is preceded by the destruction of copper(II)hexacyanoferrate(II) in an alkaline medium to form a polymeric copper(II) hydroxide, which is involved in the subsequent copper(II)–ligand complex formation. In both Cu^II–N ligand systems, two complex compounds are formed; the water-insoluble Cu₂B₂(H₂O)₂ dimer and a water-soluble product of tentative composition [CuB(HB)]^– (H₂B=ligand).     

ESR study of weak exchange interactions in binuclear copper(ii) complexes with acyldihydrazones of fluorinated β-diketones

A series of binuclear copper(ii) complexes with acyldihydrazones of aliphatic dicarboxylic acids (from malonic to adipic) and fluorinated -diketones (trifluoro- and hexafluoroacetylacetone) of composition Cu₂L·2Py (H₄L is acyldihydrazone) were studied by ESR spectroscopy. The ESR spectra of solutions of complexes with trifluoroacetylacetone acyldihydrazones have an isotropic signal with a seven-line hyperfine structure from two equivalent copper nuclei (g = 2.112, a _Cu = (39—40)·10^–4 cm^–1), which is indicative of weak exchange interactions between the paramagnetic centers due to spin density delocalization through a chain of the -bonds of the polymethylene bridge. On going to hexafluoroacetylacetone derivatives, the coupling is suppressed and the ESR spectra of solutions of such complexes show a signal with a four-line hyperfine structure (g = 2.121—2.131, a _Cu = (55—63)·10^–4 cm^–1) typical of mononuclear copper complexes.     

Bis-(tetraethylammonium)[tetraazidocuprate(II)] and catena-di-μ-1,1-azido-[di-μ-1,1-azido-bis-(2,4-dimethylpyridine)dicopper(II)]

Two new copper(II) azido complexes, namely bis-(tetraethylammonium)[tetraazidocuprate(II)] (1) and catena-di--1,1-azido-[di--1,1-azido-bis-(2,4-dimethylpyridine)dicopper(II)] (2), have been prepared and characterized by spectroscopic and crystallographic methods. Complex (1) consists of isolated NEt⁺ ₄ cations and [Cu(N₃)₄]^2– anions. The site symmetry around the copper atom in the anion is 4/m. Complex (2) features a 1 D chain structure, five coordinated square pyramidal copper(II) atoms with both azides functioning as -1,1-bridges. The i.r. spectra reveal that both complexes contain asymmetric azido ligands. The solid and solution electronic spectra of (1) and (2) show very strong absorption bands in the visible region associated with N^– ₃ Cu^II charge-transfer transitions. The e.p.r. spectra of powder samples and solutions at room temperature were recorded and discussed.     

ESR spectra of copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones

ESR spectra of binuclear copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones (H₄L) [Cu₂L·2Py], in which the coordination polyhedra are linked by the polymethylene chain with different lengths (from one to five units), were studied. The spectra of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids exhibit weak exchange interactions between the paramagnetic sites. These interactions induce seven HFS lines from two equivalent copper nuclei with the constant 40·10^–4 cm^–1 in the ESR spectra of liquid solutions. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of the complex based on heptadioic acyldihydrazone contains the signal of four HFS lines with the constant 72·10^–4 cm^–1, which is common for the copper(ii) monomeric compounds.     

Synthetic and kinetic studies on copper(II), nickel(II) and cobalt(III) complexes of 1,4,7,10,13-pentaazacyclohexadecane ([16]aneN5)

Summary The pentadentate macrocycle 1,4,7,10,13-penta-azacyclo-hexadecane [16]aneN₅=(3)=L} has been prepared and a variety of copper(II), nickel(II) and cobalt(III) complexes of the ligand characterised. The copper complex [CuL](ClO₄)₂, on the basis of its d-d spectrum, appears to be square pyramidal, while [NiL(H₂O)](ClO₄)₂ is octahedral. The copper(II) and nickel(II) complexes dissociate readily in acidic solution and these reactions have been studied kinetically. For the copper(II) complex, rate=k_H[complex][H⁺]² with k_H =4.8 dm⁶ mol^–2s^–1 at 25 °C and I=1.0 mol dm^–3 (NaClO₄) with H=43 kJ mol^–1 and S ₂₉₈ =–89 JK^–1 mol^–1. Dissociation rates of the copper(II) complexes increase with ring size in the order: [15]aneN₅ < [16]aneN₅ < [17]aneN₅. For the dissociation of the nickel(II) complex, rate=k_H[Complex][H⁺] with k_H=9.4×10^–3 dm³mol^–1 s^–1 at 25 °C and I =1.0 mol dm^–3 (NaClO₄) with H=71 kJ mol^–1 and S ₂₉₈ =–47 JK^–1mol^–1.The cobalt(III) complexes, [CoLCl](ClO₄)₂, [CoL(H₂O)]-(ClO₄)₃, [CoL(NO₂)](ClO₄)₂, [CoL(DMF)](ClO₄)₃ (DMF=dimethylformamide) and [CoL(O₂CH)](ClO₄)₂ have been characterised. The chloropentamine [CoCl([16]aneN₅)]²⁺ undergoes rapid base hydrolysis with k_OH=1.1× 10⁵dm³ mol^–1s^–1 at 25°C and I=0.1 mol dm^–3 (H=73 kJ mol^–1 and S ₂₉₈ =98 JK^–1 mol^–1). Rapid base hydrolysis of [CoL(NO₂)]²⁺ is also observed and the origins of these effects are considered in detail.     

Mono- and binuclear copper(II) complexes of saccharin with 2-pyridinepropanol synthesis,spectral, thermal and structural characterization

Mono- and binuclear copper(II) saccharinate (sac) complexes containing 2-pyridinepropanol (pypr) have been prepared and characterized by elemental analyses, i.r., u.v.–vis., magnetic measurements and single crystal X-ray diffraction. The copper(II) ion in trans-[Cu(pypr)₂(sac)₂] has –1 site symmetry and is octahedrally coordinated by two bidentate neutral pypr (N, O) and two sac (O) ligands. The binuclear copper(II) complex, [Cu₂(-pypr)₂(sac)₂], is built up around a centre of symmetry and contains two strongly distorted square–planar coordinated copper(II) ions bridged by two alkoxo groups of the deprotonated pypr ligand, which also coordinates to the copper(II) ions through its nitrogen. In contrast to the mononuclear complex, the sac ligands in the binuclear complex is N-coordinated. The binuclear complex exhibits diamagnetic behaviour. The i.r. spectra and thermal decompositions of both complexes are described.     

Preparation and properties of chiral complexes of Cu(II) with (S)-2-[(N-benzylprolyl)amino]benzaldehyde oxime,catalysts of azlactone hydrolysis

Two Cu(II) complexes of (S)-2-[(N-benzylprolyl)amino]benzaldehyde oxime (L) were isolated. The complex Cu[(LH^–1)(Cl)] is green, whereas Cu₂(LH₂)_–2 is red-brown. The structure of these complexes was proved by elemental analysis, IR and UV spectroscopy. The average molecular masses ( ) of the complexes in ethanol were determined by precision ebulliometry. The concentration dependence of the values of these complexes is consistent with the existence of the following equilibria in ethanol: Cu[(LH_–1)(Cl)] + EtOH Cu[(LH_–1)(HOEt)]⁺+Cl⁺ and [Cu₂(LH_–2)₂] + EtOH 2[Cu(LH-_–2)(HOEt)]. The equilibrium constants of these two reactions were determined. Both [Cu(LH_–1)(Cl)] and [Cu₂(LH_–2)₂] catalyze with equal efficiency the hydrolysis of 2-methyl-4-benzyl-5(4H)-oxazolone in aqueous solutions at a given pH. The UV spectra of both complexes in water at similar pH values are identical. Thus, both complexes must be interconvertible in aqueous solutions. Furthermore, the absence of any electrophoretically mobile particles in neutral aqueous buffers is an indication that the complexes [Cu₂(LH^–2)₂] and [Cu(LH^–2)(H₂O)] are the predominant species in solution under these conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2270–2275, October, 1991.     

Square-planar copper(II) complexes with a novel tetradentate amido-carboxylate ligand. Crystal structure of [Co(H2O)6][Cu(mda)] · 2H2O

A novel O—N—N—O-type tetradentate ligand H₄mda (H₄mda = malamido-N,N-diacetic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The mda^4– ligand coordinates to the copper(II) ion via two pairs of deprotonated ligating atoms (two carboxylate oxygens and two deprotonated amide nitrogens) with in-plane square chelation. A four-coordinate, square-planar geometry has been established crystallographically for the [Co(H₂O)₆][Cu(mda)] · 2H₂O complex. Structural data correlating the square-planar geometry of the [Cu(mda)]^2– unit are discussed in relation to information obtained for similar complexes. The i.r., electronic, absorption and reflectance spectra of the complexes are analysed in comparison with related complexes of known geometries.     

New unsymmetrical μ-phenoxo bridged binuclear copper(II) complexes

A series of binuclear Cu^II complexes [Cu₂XL] ⁿ⁺ having two copper(II) ions bridged by different motifs (X = OH^–, MeCO₂ ^–, or Cl^–) have been prepared using the ligands: H₂L¹ = 4-methyl-2-[N-(2-{dimethylamino}ethyl-N-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H₂L² = 4-nitro-2-[N-(2-{dimethylamino}ethyl-N-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H₂L³ = 4-methyl-2-[N-(2-{diethylamino}ethyl-N-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol and H₂L⁴ = 4-nitro-2-[N-(2-{diethylamino}ethyl-N-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol. The complexes have been characterized by spectroscopic, analytical, magnetic and electrochemical measurements. Cryomagnetic investigations (80–300 K) revealed anti-ferromagnetic exchange between the Cu^II ions (–2J in the range –50 to –182 cm^–1). The strength of anti-ferromagnetic coupling lies in the order: OAc > OH > Cl. Cyclic voltammetry revealed the presence of two redox couples, assigned to Cu^II/Cu^II/Cu^II/Cu^I/Cu^I/Cu^I. The first reduction potential is sensitive to electronic effects from the aromatic ring substituents and steric effect on the donor nitrogens (side arm) of the ligand systems.     

ESR and TPD Study of the Interaction of Nitromethane and Ammonia with HZSM-5 and CuZSM-5 Zeolites

The properties of complexes formed on HZSM-5 and CuZSM-5 zeolites in the course of ammonia and nitromethane adsorption are studied. Ammonia adsorbs on CuZSM-5 and forms two species, which decompose at different temperatures T _dec. One is due to the formation of the Cu²⁺(NH₃)₄ complex (T _dec = 450 K), and the other is assigned to ammonia adsorbed on copper(II) compounds, Cu²⁺O^– and Cu²⁺–O^2––Cu²⁺, or CuO clusters (T _dec = 650–750 K). Ammonia adsorption on Cu⁺ and Cu⁰ is negligible compared with that on the Brönsted acid sites and copper(II). Nitromethane adsorbed on HZSM-5 and CuZSM-5 at 400–500 K transforms into a series of products including ammonia. Ammonia also forms complexes with the Brönsted acid sites and copper(II) similar to those formed in the course of adsorption from the gas phase, but the Cu²⁺(NH₃)₄ complexes on CuZSM-5 are not observed. Possible structures of ammonia and nitromethane complexes on Brönsted acid sites and the Cu²⁺ cations in zeolite channels are discussed. The role of these complexes in selective NO _x reduction by hydrocarbons over the zeolites is considered in connection with their thermal stability.     

Copper(II) complexes of tetradentate N2S2 donor sets: Synthesis,crystal structure characterization and reactivity

Two mononuclear and one dinuclear copper(II) complexes, containing neutral tetradentate NSSN type ligands, of formulation [Cu^II(L¹)Cl]ClO₄ (1), [Cu^II(L²)Cl]ClO₄ (2) and [Cu^II₂(L³)₂Cl₂](ClO₄)₂ (3) were synthesized and isolated in pure form [where L¹ = 1,2-bis(2-pyridylmethylthio)ethane, L² = 1,3-bis(2-pyridylmethylthio)propane and L³ = 1,4-bis(2-pyridylmethylthio)butane]. All these green colored copper(II) complexes were characterized by physicochemical and spectroscopic methods. The dinuclear copper(II) complex 3 changed to a colorless dinuclear copper(I) species of formula [Cu^I₂(L³)₂](ClO₄)₂,0.5H₂O (4) in dimethylformamide even in the presence of air at ambient temperature, while complexes 1 and 2 showed no change under similar conditions. The solid-state structures of complexes 1, 2 and 4 were established by X-ray crystallography. The geometry about the copper in complexes 1 and 2 is trigonal bipyramidal whereas the coordination environment about the copper(I) in dinuclear complex 4 is distorted tetrahedral.     

Novel trinuclear copper(II) complexes with α,β-unsaturated carboxylates and imidazole

A MeOH solution of imidazole reacts with Cu₂A₄(H₂O)₂ [A = CH₂=CHCO^– ₂, CH₂=C(Me)CO^– ₂] to yield novel trinuclear copper(II) carboxylate complexes of general formula: Cu₃A₅(OH)(imH)₃ [(1) A=CH₂=CHCO^– ₂; (2) A = CH₂=C(Me)CO^– ₂; imH = imidazole]. The crystal structure of (2) has been determined. The geometry of one copper(II) atom is distorted trigonal bipyramidal, and the other two copper(II) atoms are distorted square-planar. The i.r. spectra show the presence of the absorption bands of both bidentate ₂-O,O and monodentate carboxylate ligands. The electronic reflectance spectra in the solid state suggest that the d–d transitions of complexes are in a trigonal bipyramidal ligand field and a square-planar ligand field. Room temperature X-band e.s.r. spectra of powdered samples with g _av = 2.140 for (1) and g _av = 2.092 for (2), indicate that there is no spin coupling between the copper(II) atoms.     

Complexation of copper(I) by thiourea in acidic aqueous solution

The interaction of copper(II) and copper(I) with thiourea(Tu) has been investigated by UV and visible spectrophotometry. Over the range of concentrations of copper(I) and Tu(0.1–20)×10^–3 mol-dm^–3 in acid aqueous solutions there are two complexes, CuTu₂ ⁺ (log ₂=11.1) and the other has the ratio Cu/Tu=1/1 with the likely composition Cu₂Tu₂ ²⁺ with log ₂₂=18.5. By the determination of copper(0) solubility in acid thiourea solution and potentiometric measurements it was shown that the potential of the copper electrode is that of a non-equilibrium (corrosive) electrode.     

Electrochemical synthesis and magnetic studies of neutral transition metal imidazolates and pyrazolates

Summary The single-step electrochemical synthesis of neutral transition metal complexes of imidazole, pyrazole and their derivatives has been achieved at ambient temperature. The metal was oxidized in an Me₂CO solution of the diazole to yield complexes of the general formula: [M(Iz)₂] (where M = Co, Ni, Cu, Zn; Iz = imidazolate); [M(MeIz)₂] (where M = Co, Ni, Cu, Zn; MeIz = 4-methylimidazolate); [M(PrⁱIz)₂] (where M = Co, Ni, Cu, Zn; PrⁱIz = 2-isopropylimidazolate); [M(pyIz)_n] (where M = Co^III, Cu^II, Zn^II; pyIz = 2-(2-pyridyl)imidazolate); [M(Pz)_n] (where M = Co^III, Ni^II, Cu^II, Zn^II; Pz = pyrazolate); [M(ClPz)_n] and [M(IPz)_n] (where M = Co^III, Ni^II, Cu^II, Zn^II; ClPz = 4-chloropyrazolate; IPz = 4-iodopyrazolate); [M(Me₂Pz)_n] (where M = Co^II, Cu^I, Zn^II; Me₂Pz = 3,5-dimethylpyrazolate) and [M(BrMe₂Pz)_n] (where M = Co^II, Ni^II, Cu^I, Zn^II; BrMe₂Pz = 3,5-dimethyl-4-bromopyrazolate). Vibrational spectra verified the presence of the anionic diazole and electronic spectra confirmed the stereochemistry about the metal centre. Variable temperature (360-90 K) magnetic measurements of the cobalt and copper chelates revealed strong antiferromagnetic interaction between the metal ions in the lattice. Data for the copper complexes were fitted to a Heisenberg (S= ) model for an infinite one-dimensional linear chain, yielding best fit values of J=–62––65cm^–1 andg = 2.02–2.18. Data for the cobalt complexes were fitted to an Ising (S= ) model with J=–4.62––11.7cm^–1 andg = 2.06–2.49.     

Colloidal copper in aqueous solutions: radiation-chemical reduction,mechanism of formation,and properties

Colloidal copper has been obtained by -irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When Cu^II is not entirely incorporated into the complex with PEI, disproportionation of Cu^I aqua complexes formed affords the metal, along with Cu₂O. Reduction of the PEI complex of Cu^I by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 25–30, January, 1994.     

Copper(II) and nickel(II) complexes of mono-oxocyclam(5-oxo-1,4,8,11-tetraazacyclotetradecane). Synthetic and potentiometric studies

Summary The macrocyclic mono-oxotetraamine, 5-oxo-1,4,8,11-tetraazacyclotetradecane (mono-oxocyclam=LH) has been prepared by reaction of methyl acrylate with 2,3,2-tetra(1,9-diamino-3,7-diazanonane). The protonation constants of the ligand are log K₁=9.40, log K₂=6.65 and log K₃=2.87 at 25 °C (I=0.1 mol dm^–3 NaClO₄). Detailed potentiometric studies of the interaction of the base with copper(II) and nickel(II) have been carried out. In the pH range 2.5–7.0 two complexes, [CuLH]²⁺ and [CuL]⁺, form; the deprotonated complex being 100% abundant at pH 7. For nickel(II), only [NiL]⁺ forms (log _11–1 = 3.90), the yellow low spin nickel complex reaching its maximum concentration above pH 6. The [CuL][ClO₄] · H₂O and [NiL][ClO₄] 0.5 H₂O complexes have been characterised in the solid state. The nickel(II) complex is square planar with a d-d band at 22625 cm^–1.