Synthesis and structural analysis of copper(II) cysteine complexes

This report describes the synthesis and structural analysis of stable copper(II) cysteine complexes. Pale pink copper(II) cysteine complexes were synthesized in mole ratios of 1:2, 1:4, and 1:6 of copper(II):cysteine in ethanol. Infrared spectroscopy and X-ray absorption spectroscopy confirmed that copper(II) binding occurred via the thiol ligand of cysteine. XANES analysis showed that the oxidation state of copper remained as copper(II) and the local atomic geometry was similar in all of the cysteine complexes. The EXAFS data indicate that the copper(II) cysteine complexes are forming ring type structures with sulfur ligands from the cysteines acting as bridging ligands. X-ray diffraction revealed that the copper(II) cysteine complexes formed monoclinic cells with maximum crystallinity found in the 1:4 copper(II):cysteine complex.     

Synthesis and characterization of ruthenium(II) complexes bearing the bis(2-pyridylmethyl)amine ligand

The reaction of [Ru(CO)₂Cl₂]_n with bis(2-pyridylmethyl)amine (bpma) in refluxing ethanol followed by anion exchange yields two products: cis,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1a, 71%) and trans,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1b, 29%). Reaction of 1a with AgBF₄ in acetone, followed by acetonitrile and then anion exchange gave cis,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2a). In the same way, 1b afforded trans,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2b). Reaction of depolymerized [Ru(CO)₂Cl₂]_n with bpma in ethanol at room temperature afforded cis,cis-[Ru(η²-bpma)(CO)₂Cl₂] (3). In refluxing ethanol, 3 was converted to cis,fac-[Ru(bpma)(CO)₂Cl]Cl (1a-Cl). Heating 3 in chlorobenzene afforded 1b-Cl, exclusively; heating 3 in ethylene glycol gave mainly 1a-Cl. Heating 1a-Cl in ethanol resulted in no isomerization, but heating in chlorobenzene gave a mixture of 3 and 1b-Cl. Anion exchange for PF₆ with 1a-Cl and 1b-Cl afforded 1a and 1b, respectively, whereas anion exchange for BPh₄ afforded 1a-BPh₄. Compounds 1a, 1b, 2a and 3 have been structurally characterized.     

Syntheses and characterization of copper complexes with the ligand 2-aminoethyl(2-pyridylmethyl)-1,2-ethanediamine (apme)

Copper(I)/(II) complexes with the ligand 2-aminoethyl(2-pyridylmethyl)1,2-ethanediamine (apme, abbreviated as PDT in the literature as well) were prepared and characterized. Crystal structures of the copper(I) complexes, [Cu₂(apme)₂]X₂ (1, 2; X = ClO₄, CF₃SO₃), showed that they are dinuclear, in contrast to the trigonal bipyramidal copper(II) complexes [Cu(apme)Cl]BPh₄ (3) and [Cu(apme)(DMF)](BPh₄)₂ (4). 1 and 2 could be investigated in solution by NMR spectroscopy and 3 and 4 by cyclovoltammetry. From the results of these studies it is clear that in solution equilibria between the dinuclear complexes 1/2 and another species exist, most likely the monomeric [Cu(apme)CH₃CN]⁺. Time-resolved UV/vis spectra at low temperatures allowed the spectroscopic detection of dioxygen adduct complexes as reactive intermediates during the oxidation of 1/2 with dioxygen that seem to play an important role in copper enzymes such as peptidylglycine--hydroxylating monooxygenase (PHM).     

Synthesis and structural characterization of copper(II) bishexafluoroacetylacetonate complexes with N-donor ligands

The reactions of Cu(hfac)₂ with different N-donor ligands such as 2-ethynylpyridine and imidazole give copper complexes Cu(hfac)₂(ethynylpyridine) (1) and Cu(hfac)₂(ImH)₂ (2), respectively. The reaction of Cu(hfac)₂ · (ethynylpyridine) (1) and ethynylpyridine with oxygen in tmeda (tmeda = N,N,N′,N′-tetramethylethylenediamine) in the presence of copper(I) chloride gives Cu(hfac)₂(tmeda) (3). Finally, [Cu(hfac)₂(H₂O)]₂(μ-TCNE) (4) was prepared by reaction of Cu₂O on the free acid β-diketone in the presence of TCNE (TCNE = tetracyanoethylene) (ratio 1.5:1:1), under an atmosphere of oxygen-free Ar. The previously synthesized Cu(hfac)TCNE proceeded further reaction by disproportionation, yielding [Cu(hfac)₂(H₂O)]₂(μ-TCNE). All new compounds have been structurally characterized and their thermal properties were examined by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).     

Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO₄ (1), [Co(TPA)Br]ClO₄ (2), [Co(TPA)(H₂O)]Cl(ClO₄) (3) and [Co₂(TPA)₂(μ-tp)](ClO₄)₂ · 2H₂O (4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV-vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2-300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl⁻ ion in 1, Br⁻ ion in 2, coordinated oxygen atom from H₂O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1-3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣D∣ = 7.3 cm⁻¹, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm⁻¹. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique - the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.     

Synthesis, structural characterization and redox properties of copper(II) and manganese(II) complexes containing tridentate (N-(2-methylpyridine)-2-aminomethyl benzoate) ligand

Two new complexes, [Cu(mamba)₂] and [Mn(mamba)₂] (mamba⁻, N-(2-methylpyridine)-2-aminomethyl benzoate) were synthesized and characterized by X-ray crystallography. Whereas the [Cu(mamba)₂] complex crystallizes in a monoclinic P2₁/c space group, the [Mn(mamba)₂] complex crystallizes in a triclinic space group. The nature of the metal ion greatly influences the lattices and the molecular structures of the compounds. In the crystal lattice of the copper complex are four cocrystallized methanol solvent, which are all involved in building six strong H-bonds with the complex. However, the lattice for the manganese complex contain only one cocrystallized methanol, along with one NaClO₄, that is also involved in making one H-bond with the [Mn(mamba)₂] unit. Nevertheless, the sodium ion is coordinated to the ClO₄⁻, the methanol and two [Mn(mamba)₂] to form a stable extended chain metal complex. Electrochemical studies indicated that both complexes undergo quasi reversible one electron reduction in acetonitrile.     

Ditopic bis(oxazolines): Synthesis and structural studies of zinc(II), copper(II) and nickel(II) complexes

The synthesis, crystal structures, magnetic and spectroscopic properties of zinc(II), nickel(II) and copper(II) dinuclear complexes 2-4 of a novel dinucleating polyoxazoline ligand 1 are reported. X-ray analysis revealed that the three complexes are centrosymmetric dinuclear species with an overall S shape, the bisoxazoline moieties pointing toward the aromatic core of the molecule. Magnetic susceptibility measurements suggest that there is a very weak exchange interaction between the copper or nickel ions in complexes 3 and 4.     

Synthesis, structural and corrosion inhibition studies on cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone

Cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, electronic, IR, NMR and ESR spectral techniques. The molecular structures of ligand and its copper(II) complex have been determined by single crystal X-ray diffraction technique. The Cu(II) complex possesses a CuN₂O₂ chromophore with a considerable delocalization of charge. The structure of the complex is stabilized by intermolecular π–π stacking and C–H?π interactions. Hatbh acts as a monobasic bidentate ligand in all the complexes bonding through a deprotonated C–O⁻ and >CN groups. Electronic spectral studies indicate an octahedral geometry for the Ni(II) complex while square planar geometry for the Co(II) and Cu(II) complexes. ESR spectrum of the Cu(II) complex exhibits a square planar geometry in solid and in DMSO solution. The trend g_|| > g_⊥ > 2.0023 indicates the presence of an unpaired electron in the d_x²-y² orbital of Cu(II). The electro-chemical study of Cu(II) complex reveals a metal based reversible redox behavior. The Ni(II) complex shows exothermic multi-step decomposition pattern of the bonded ligand. The ligand and its most of the metal complexes show appreciable corrosion inhibition properties for mild steel in 1 M HCl medium. [Co(atbh)₂] complex exhibited the greatest impact on corrosion inhibition among the other compounds.     

Synthesis, characterization, and cytotoxic activity of copper(II) and platinum(II) complexes of 2-benzoylpyrrole and X-ray structure of bis[2-benzoylpyrrolato(N,O)]copper(II)

Copper(II) and platinum(II) complexes of 2-benzoylpyrrole (2-BZPH) were synthesized and characterized with IR, 1H and 13C NMR spectroscopies and coordination geometry with ligands arranged in transoid fashion. The crystal structure of [Cu(II)(2-BZP)2] was determined by X-ray diffraction. Death of complex treated Jurkat cells was measured by flow cytometry. The bis-chelate complexes [Cu(II)(2-BZP)2] and [Pt(II)(2-BZP)2] adopt square-planar coordination geometry with ligands, arranged in transoid fashion. Concentrations of 1-10 microM Platinum(II) complexes reduced cell survival from 100% to 20%, in contrast to the copper(II) complex which caused no cell death at a concentration of 10 microM. While the Pt(II) complexes may have damaged DNA to induce cell death, treatment with the Cu(II) complex did not induce Jurkat cell death.     

Synthesis and structural diversity of 2-pyridylmethylideneamine complexes of zinc(II) chloride

The addition reactions of zinc(II) chloride to N-substituted pyridine-2-carbaldimines [Py-CHNR, R = Me (1a), Ph (1b), Bz (1c), allyl (1d)] lead to different complexes dependent on the N-bound substituent R. The 1:1 complexes show molecular structures of the type [(Py-CHNR)ZnCl₂] for R = methyl (2a), phenyl (2b), and allyl (2d) with a distorted tetrahedral environment for the zinc atom. The zinc complex with the N-methylated pyridine-2-carbaldimine also forms a dimer of the type [(Py-CHNR)ZnCl₂]₂ (2a)₂ with a square pyramidal coordination sphere of zinc. A 3:2 stoichiometry is observed for R = benzyl and an ion pair of the type [Zn(Py-CHNR)₃]²⁺ [ZnCl₄]²⁻ (2c) is found in the solid state.     

Synthesis, characterization of some organolanthanide complexes containing 2-pyridylmethyl substituted fluorenyl ligand and catalytic activity of organolanthanide(II) complexes

A series of organolanthanide complexes with 2-pyridylmethyl substituted fluorenyl ligand were synthesized via reaction of [(Me₃Si)₂N]₃Ln^III(μ-Cl)Li(THF)₃ (Ln = Yb, Eu, Nd, Y) with the functionalized fluorene compound. Treatment of [(Me₃Si)₂N]₃Ln^III(μ-Cl)Li(THF)₃ (Ln = Yb, Eu) with 2 equiv. of C₅H₄NCH₂C₁₃H₉ (1) at 60-80 °C in toluene afforded the corresponding organolanthanide(II) complexes with formula [η⁵:η¹- C₅H₄NCH₂C₁₃H₈]₂Ln [Ln = Yb (2), Eu (3)] via tandem silylamine elimination/homolysis of the Ln-N bond reaction. Reaction of [(Me₃Si)₂N]₃Ln^III(μ-Cl)Li(THF)₃ (Ln = Y, Nd) with 2 equiv. of C₅H₄NCH₂C₁₃H₉ in toluene at 80 °C produced the corresponding organolanthanide(III) complexes with formula [η⁵:η¹-C₅H₄NCH₂C₁₃H₈]₂LnCl [Ln = Y (4), Nd (5)]. Complexes 4 and 5 could also be prepared by treatment of 2 equiv. of lithium fluorenide [η⁵:η¹-C₅H₄NCH₂C₁₃H₈]Li(THF)₂ (6) with corresponding LnCl₃. All compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of complexes 4 and 6 were additionally determined by single-crystal X-ray analyses. The catalytic properties of the divalent organolanthanide complexes 2 and 3 on the ring-opening polymerization of ε-caprolactone (CL) have been studied. The temperatures, solvents effects on the catalytic activities of the complexes were examined.     

Synthesis and characterization of an N-coordinated amidate copper(II) complex of deprotonated N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide

The title ligand, N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide (DIPMAE-H), was prepared by a nucleophilic substitution reaction between N-(2,6-diisopropyl)phenyl-2-bromoethanamide and bis-(2-pyridylmethyl)amine. An analogous ligand (TBPMAE-H) in which the 2,6-diisopropylphenyl group was substituted for a tert-butyl group was also prepared in this manner. Then, [(DIPMAE-H)CuBr]⁺Br⁻ and [(TBPMAE-H)CuBr]⁺Br⁻ were prepared by heating one equivalent of ligand and CuBr₂ in CH₃CN. In both compounds the geometry about the copper center is square pyramidal with distortions due to the geometrical constraints of the ligand. The amide oxygen occupies the axial position, and the three amine nitrogens and the bromide ligand form the basal plane of the square pyramid. Pairs of complexes in the unit cell are associated via weak donation of a lone pair on the bromide ligand of one complex to the copper center of another (Cu?Br distances in the range of 3.3576-3.4022 Å).The title compound, (DIPMAE)CuBr, was prepared by deprotonation of [(DIPMAE-H)CuBr]⁺Br⁻ using NaH. The key feature of (DIPMAE)CuBr is the amidate group η¹- and N-coordinated to the copper center. The compound also exhibits distorted trigonal bipyramidal coordination geometry with the bromide and tertiary amine donors occupying the axial sites and the amidate and pyridyl donors occupying the equatorial positions. The copper atom is displaced from the trigonal plane towards the bromide donor apex due to the geometrical demands of the ligand.     

Synthesis of copper(II) and nickel(II) complexes of N-(hydroxyalkylaminoalkyl)salicylamides

Copper(II) and nickel(II) complexes are prepared of potentially quadridentate ligands (LH₃), N-{2-(2- hydroxyethylamino)ethyl}- (seeH₃), N-{3-(2-hydroxy- ethylamino)propyl}- (steH₃), and N-{2-(3-hydroxypropylamino)ethyl}-salicylamide (setH₃). The nickel complexes Na[Ni(see)] and Na[Ni(set)]·1/2H₂O are diamagnetic and square-planar, in which the ligands act as a quadridentate one coordinated through secondary amino-N, and deprotonated phenolic-O, alcoholic-O, and amido-N atoms. The three copper complexes Na [CuL]·H₂O (L = see, ste, set) with a normal magnetic moment have a similar square-planar structure. In another type complexes Cu(LH)·H₂O (LH = seeH, setH) an alcohol group is not deprotonated. Two isomers are present in Cu(seeH)·H₂O: one has a normal and the other a subnormal magnetic moment. The difficulty of complex formation of steH₃ may be attributed to an unfavourably fused 6-6-5 membered chelate ring with strain.     

Dinuclear nickel(II) and zinc(II) complexes of 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methylphenol

Reaction of the symmetrical proligand H₂L with metal(II) acetate and a counteranion to promote crystallisation has given the homodinuclear complexes [Zn₂L(OAc)₂](BF₄)]·2MeOH and [Ni₂L(OAc)₂](BF₄)]·2MeOH the crystal structures of which are reported. These show the presence of a triply bridging (μ-cresolato)bis(μ-carboxylato) dimetal core.     

Synthesis, structural characterization, formation constants and in vitro cytotoxicity of phenanthroline and imidazolidine-2-thione copper(II) complexes

The synthesis, crystal structures, physicochemical properties and complex formation constants of [Cu(phen)₂(L)](ClO₄)₂ complexes, where phen is 1,10-ortho-phenanthroline and L is a series of substituted imidazolidine-2-thione, have been studied. Single crystal X-ray diffraction revealed a distorted trigonal-bipyramidal geometry for all the molecules. The complex formation constants were determined in nonaqueous media by spectrophotometric measurements. Testing copper(II) complexes in mouse neuroblastoma N2a cells persistently infected with the 22L strain of the scrapie prion protein (22L-N2a) resulted in high cytotoxicity but no antiprion activity at nontoxic doses.     

Synthesis and structural characterization of cadmium(II) complexes with 2-(2-pyridyl)imino-N-(2-thiazolin-2-yl)thiazolidine (PyTT)

We have carried out the synthesis of the cadmium coordination compounds [Cd(NO₃)₂(PyTT)(H₂O)] (1) and [CdCl₂{(μ-Cl)₂CdCl(μ-Cl)(μ-PyTT)Cd}₂]_n (2), together with their structural determination by means of X-ray diffraction. The compounds were also characterized through elemental analysis and infrared spectroscopy. The first complex presents a distorted pentagonal bipyramidal geometry with the axial positions occupied by one oxygen atom from a water molecule and a second one from a nitrate ion which acts as a monodentate ligand, whereas the equatorial plane contains three nitrogen atoms from the organic moiety and two oxygen atoms coming from the other nitrate group, which is bidentate. The structure of the second complex consists of parallel sheets linked by van der Waals forces, each one made up of structural units [CdCl₂{(μ-Cl)₂CdCl(μ-Cl)(μ-PyTT)Cd}₂], which possesses two PyTT ligands, 10 bridging chloro ligands and 5 cadmium(II) centres belonging to three environment types: octahedral CdN₂Cl₄, octahedral CdCl₆, on which a centre of symmetry is located, and tetrahedral CdNCl₃, present in a 2:1:2 ratio.     

Synthesis, structural studies and solubility properties of zinc(II), nickel(II) and copper(II) complexes of bulky tris(triazolyl)borate ligands

Tris(triazolyl)borate (Ttz) ligands are sterically similar to tris(pyrazolyl)borate (Tp) but complexes of Ttz show improved solubility in water and alcohols due to their propensity for forming hydrogen bonds. Recently developed bulky tris(triazolyl)borate ligands can produce four and five coordinate transition metal complexes and serve as models for enzyme active sites in an aqueous environment. Herein we report the synthesis of such complexes, i.e. (Ttz^tBu,Me)ZnCl, (Ttz^tBu,Me)ZnBr, (Ttz^tBu,Me)NiCl, and (Ttz^tBu,Me)CuCl, which were analyzed by X-ray crystallographic and spectroscopic methods [Ttz^tBu,Me = tris(3-t-butyl-5-methyl-1,2,4-triazolyl)borate]. (Ttz^tBu,Me)ZnCl crystallizes as two different polymorphs with cubic and monoclinic symmetry. Both polymorphs of (Ttz^tBu,Me)ZnCl and (Ttz^tBu,Me)ZnBr have tetrahedral zinc atoms whereas the geometries at the metal in (Ttz^tBu,Me)NiCl and (Ttz^tBu,Me)CuCl are distorted tetrahedral. All complexes are methanol soluble and they also dissolve in methanol/water mixtures with up to 60% water.     

Copper(II) PMDTA and copper(II) TMEDA complexes: precursors for the synthesis of dinuclear dicationic copper(II) complexes

Copper(II) cations coordinated with PMDTA (pentamethyldiethylenetriamine) and TMEDA (tetramethylethylenediamine) possess a high synthetic potential. The synthesis of these cations was carried out by metathesis reactions with silver salts. The cationic copper(II) complexes, [Cu(PMDTA)(Me₂CO)Cl]⁺, [Cu(PMDTA)(H₂O)Cl]⁺, [Cu(PMDTA)(DMF)]⁺, [Cu(PMDTA)Cl]⁺, [Cu(PMDTA)OAc]⁺, [Cu(PMDTA)(MeCN)₂]²⁺, [Cu₂(TMEDA)₂Cl₃]⁺ and [Cu(TMEDA)(MeCN)₃]²⁺ were synthesised as PF₆ salts, crystallised and characterised by single-crystal X-ray diffraction.     

Synthesis and structure of copper(II) complexes of two new poly(2-pyridylalkyl)diamine ligands

The new pentapyridyldiamine ligand, L¹, which incorporates two bis(2-pyridylethyl)amine donor domains held together by a 2,6-dimethylenepyridine linker, is readily prepared. In the presence of metal salts, L¹ is unstable due to facile elimination of vinyl pyridine. Complexes of L¹ are therefore difficult to isolate. Nonetheless, a novel copper dimer [Cu₂(L¹)(μ-OH)(CH₃CN)](ClO₄)₃ has been isolated in small quantities along with the interesting monomer [Cu(L²)](ClO₄)₂, in which L² is the tetrapyridyldiamine ligand derived from the decomposition of L¹ by loss of one pyridylethyl `arm'. The crystal structures of the two complexes are reported: the [Cu<sub>2</sub>(L<sup>1</sup>)(μ-OH)(CH<sub>3</sub>CN)]<sup>2+</sup> cation exhibits a μ-hydroxo-bridged dicopper(II) core and a coordinated acetonitrile molecule, akin to a putative intermediate in nitrile hydrolysis, and the chiral [Cu(L<sup>2</sup>)]<sup>2+</sup> cation is revealed to have a five-coordinate copper(II) centre that is stabilised by an intramolecular hydrogen-bond between the 2° amine group and a pendant pyridylethyl `arm'.