A temperature-dependent dynamic rearrangement of cis-(R,S)-[Pd(egta)]2– (egta4–=glycine,N,N′-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]) in aqueous solution

The cis-(R,S)-[Pd(egta)]2– complex, egta4–=glycine, N,N-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]), has been examined by 1H- and 13C-n.m.r. methods over the 18.0 to 95.0°C range in D2O. A dynamic process occurs above 65°C which makes the protons on the NCH2 functionalities of the egta tether become 1H-n.m.r. equivalent. The two states that interconvert coalesce at 81°C. Evidence from 13C-n.m.r. spectra obtained at 81°C show that the in-plane coordinated carboxylates are not lost, but rather a pendant carboxylate becomes attached with loss of the central imino donor. The resultant palladium(II)NO3 intermediate is able to reform cis-(R,S)-[Pd(egta)]2– or, presumably, give trans-(R,R)-[Pd(egta)]2–. The rate limiting step occurs with a rate constant of 178s–1 at 81°C and an activation energy of 20.5kJ/mol. However, competitive aquation of glycinato donors above 85°C prevents isolation of a stable trans-(R,R)-[Pd(egta)]2– isomer.     

Copper(II) and palladium(II) complexes of N,N′-bis(2-hydroxyethyl)stilbenediamine

A new 1,2-diamine ligand, N,N-bis(2-hydroxyethyl)stilbenediamine (L), has been prepared by reduction of the condensation product of benzaldehyde with 2-aminoethanol with Al amalgam. Mononuclear complexes of the [CuL(H₂O)]X₂ type where X=Cl^– or AcO^– with Cu^II and PdLCl₂ with palladium(II) have been prepared and characterized by elemental analysis and i.r., u.v.–vis. or ¹H-n.m.r. spectroscopy.     

Thermal behavior of Mannich base N,N′-tetra(4-antipyrylmethyl)-1,2 diaminoethane (TAMEN) and its binuclear complexes

The thermal decomposition of Mannich base N,N′-tetra(4-antipyrylmethyl)-1,2-diaminoethane (TAMEN), and its Ni(II), binuclear complex, Ni₂(TAMEN)Cl₄, in air and in nitrogen atmosphere, were investigated. X-ray powder diffractometry, infrared spectroscopy and simultaneous thermogravimetry-differential thermal analysis (TG-DTA), have been used to characterize and to study the thermal behavior of these compounds. The results provided information concerning the stoichiometry, crystallinity, thermal stability and decomposition mechanism of the compound.     

Thermochemistry of Cu(II) and Ni(II) complexes with N,N-di-n-butyl-N′-thenoylthiourea and N,N-di-iso-butyl-N′-thenoylthiourea

Two substituted N-acylthioureas and the respective Ni(II) and Cu(II) complexes were synthesized, namely: N,N-di-n-butyl-N′-thenoylthiourea (Hnbtu); N,N-di-iso-butyl-N′-thenoylthiourea (Hibtu); bis[N,N-di-n-butyl-N′-thenoylthioureato]nickel(II), [Ni(nbtu)₂]; bis[N,N-di-n-butyl-N′-thenoylthioureato]copper(II), [Cu(nbtu)₂]; bis[N,N-di-iso-butyl-N′-thenoylthioureato]nickel(II), [Ni(ibtu)₂]; bis[N,N-di-iso-butyl-N′-thenoylthioureato]copper(II), [Cu(ibtu)₂]. The standard (p^° = 0.1 MPa) molar enthalpies of formation and sublimation of the two N-acylthioureas were measured, at T = 298.15 K, by rotating-bomb combustion calorimetry and Calvet microcalorimetry, respectively. The standard (p^° = 0.1 MPa) molar enthalpies of formation of the Ni(II) and Cu(II) complexes were determined, at T = 298.15 K, by high precision solution–reaction calorimetry. From the results obtained, the enthalpies of hypothetical metal–ligand and metal–metal exchange reactions, in the gaseous phase, were derived, thus allowing a discussion of the gaseous phase energetic difference between the complexation of Ni(II) and Cu(II) to 1,3-ligand systems with (S,O) ligator atoms.     

Synthesis,crystal structures and catalytic activities of new palladium(II)–bis(oxazoline) complexes

Palladium–bis(oxazoline) complexes (Pd-BOX-A and Pd-BOX-B) were synthesized and characterized by ¹H, ¹³C NMR, IR and elemental analysis. The molecular structures of the complexes were confirmed by single-crystal X-ray analysis. In both cases, the palladium center is coordinated by the nitrogen atoms of the two oxazoline rings and two chloride ligands in a distorted square planar geometry. Despite the fact that the bis(oxazoline) ligand is achiral, the asymmetrical substitution on the phenyl spacer and the rigid backbone of the complex Pd-BOX-A induce inherent chirality and the compound crystallizes as a racemic mixture. Both complexes were found to be highly effective catalysts for Suzuki–Miyaura, Mizoroki–Heck and Sonogashira cross-coupling reactions. They also show excellent catalytic activities toward carbonylative coupling reactions.     

Synthesis and characterization of binuclear μ-oxalato nickel(II), copper(II) and zinc(II) complexes with 3,3′-diamino-N-methyl-dipropylamine or trans-1,2-diaminocyclohexane

New binuclear complexes of the type [(Ni(Medpt)NO₃)₂ox] (1) (Medpt=3,3′-diamino-N-methyl-dipropylamine, H₂ox=oxalic acid), [(Ni(dach)₂)₂ox]NO₃·2H₂O (2) (dach=trans-1,2-diaminocyclohexane), [(Cu(Medpt))₂ox]X₂·yH₂O (X=NO₃, y=2 2/3 (3); X=ClO₄, y=0 (4)) and [(Zn(dach)₂)₂ox](ClO₄)₂·2H₂O (5) have been prepared and characterized by IR and UV–Vis spectroscopies. Spectroscopic data are consistent with oxalate-bridged structures between six-coordinated (N₃O₃ or N₄O₂) Ni(II) (compounds 1 or 2), five-coordinated (N₃O₂) Cu(II) (compounds 3 and 4) or six-coordinated (N₄O₂) Zn(II) (compound 5). The crystal structure of [(Cu(Medpt))₂ox](NO₃)₂·2 2/3 H₂O (3) has been determined by single-crystal X-ray analysis. The structure of (3) consists of centrosymmetric binuclear cations [(Medpt)Cu(ox)Cu(Medpt)]²⁺, nitrate anions and water molecules of crystallization. The copper atom is five-coordinated by two oxalate–oxygen and three Medpt–nitrogen atoms, in a hybrid arrangement between trigonal–bipyramidal and square–pyramidal. The temperature dependence of magnetic susceptibility (1.8–300 K) was measured for compounds 1–4. Magnetochemical measurements show that Ni(II) complexes are antiferromagnetically coupled, J=−29.4 (1) and −32.7 cm⁻¹ (2) (H=−JS₁S₂) while the Cu(II) complexes present a very weak coupling, J=−2.6 (3) and +1.9 cm⁻¹ (4), being antiferro- and ferromagnetic in nature.     

Manganese(II), nickel(II) and copper(II) complexes of (1,3-bis-aminomethyl) cyclohexane-N,N,N′,N′-tetrakisbenzimidazole

Summary Mn^II, Ni^II and Cu^II complexes of (1,3-bis-aminomethyl)-cyclohexane-N,N,N,N-tetrakisbenzimidazole (CDTB) have been prepared and characterized by spectral techniques. The complexes are monomeric and pseudo-octa-hedral, as evidenced by their e.p.r. spectra and analytical data. Parameters ², ², ² and for Cu^II complexes, and the crystal field splitting parameter (10 Dq) together with the Nephelauxetic ratio (), for Ni^II complexes, are reported.     

Novel 2,2′-bipyridine palladium(II) complexes with glycine derivatives: synthesis, characterization, cytotoxic assays and DNA-binding studies

The two water-soluble designed palladium(II) complexes, [Pd(bpy)(pip-Ac)]NO₃ and [Pd(bpy)(mor-Ac)]NO₃, (where bpy is 2,2′-bipyridine, pip-Ac is 1-piperidineacetato and mor-Ac is 4-morpholineacetato) have been synthesized and characterized by elemental analyses, molar conductivity measurements and spectroscopic methods (FT-IR, ¹H NMR, UV–Vis). The complexes have been tested for in vitro cytotoxic activity against human breast cancer cell line, T47D. The binding of these complexes with DNA has been investigated by absorption spectroscopy, fluorescence titration spectra, EB displacement and gel chromatography. The results suggest that the complexes can bind to DNA cooperatively through a static mechanism at low concentrations (~0.57 μM). The thermodynamic parameters indicated that the van der Waals and hydrogen binding might play a major role in the interaction of these complexes with DNA.     

N,N′-(1,2-phenylene)bis­(pyridine-2-carboxamide) and N,N′-(1,2-cyclohexanediyl)bis(pyridine-2-carbox­amide) toluene hemisolvate

The crystal structures of N,N′-(1,2-phenyl­ene)­bis­(pyridine-2-carbox­amide), C₁₈H₁₄N₄O₂, (I), and N,N′-(1,2-cyclo­hexane­diyl)­bis­(pyridine-2-carbox­amide) have been determined, the latter compound as the toluene hemisolvate, C₁₈H₂₀N₄O₂·0.5C₇H₈, (II). In (I), the benzene ring is nearly coplanar with one of the pyridine rings and forms a dihedral angle of 59.4 (1)° with the other. However, in (II), the dihedral angle of the two pyridine rings is 70.0 (1)°.     

Synthesis and X-ray crystal structures of N,N,N′,N′-tetraalkylpyridine-2,6-dithiocarboxamides (S-dapt) complexes of cobalt(II) and nickel(II)

Reactions of anhydrous CoX₂ (X?=?Br^?, SCN^?) and Ni(ClO₄)₂ with N,N,N′,N′-tetraisobutylpyridine-2,6-dithiocarboxamides (S-dbpt), N,N,N′,N′-tetraisopropyl pyridine-2,6-dithiocarboxamides (S-dppt), and N,N,N′,N′-tetraethylpyridine-2,6-dithiocarboxamides (S-dept) lead to the formation of [Co(S-dbpt)Br₂] (1), [Co(S-dppt)(SCN)₂] (2), and [Ni(S-dept)₂]·(ClO₄)₂·H₂O (3), respectively. The X-ray crystal structures of the three S-dapt ligands and three complexes along with spectroscopic analyzes are presented. The molecular structure investigations of the S-dapt ligands show that the thiamide planes are twisted with respect to the pyridine ring, which is more in the case of phenyl groups. The structures of the Co(II) complexes reveal that an increase in steric crowding on the amide side arms of the ligands has no substantial effect on the geometry adopted by the corresponding complexes. The Co(II) gives only 1?:?1 five-coordinate, ion-paired complexes with a distorted square pyramidal geometry. Ni(II), on the other hand, prefers an octahedral geometry with 1?:?2 metal–ligand ratio. The coordination behavior of S-dapt has been compared to the analogous oxo(O-daap) ligands. Lesser propensity of S atom to get involved in H-bonding interactions ensures an S-N-S type of tridentate coordination by S-dapt.     

Synthesis,X-ray structure,DFT and thermodynamic studies of mono- and binuclear palladium(II) complexes involving 1,4-bis(2-hydroxyethyl)piperazine,bio-relevant ligands and 4,4′-bipiperidine

[Pd(BHEP)Cl₂] (BHEp = 1,4-bis(2-hydroxyethyl)piperazine) was synthesized and characterized. The palladium center has a typical square-planar geometry with a tetrahedral distortion. The alcohol groups of the ligand do not participate in binding to Pd(II). The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program and compared with experimental results. The stoichiometry and stability constants of the complexes formed between [Pd(BHEP)(H₂O)₂]²⁺ and some selected amino acids, peptides, and DNA constituents were investigated at 25 °C and 0.1 M ionic strength. The binuclear complex [(H₂O)(BHEP)Pd(Bip)Pd(BHEP)(H₂O)]⁴⁺ was detected, where Bip = 4,4′-bipiperidine. Inosine, uracil, and thymine interact with the binuclear complex via substitution of both coordinated water molecules. The potentiometric results were complimented by spectroscopic measurements. The concentration distribution diagrams of the various species formed were evaluated.     

Hydrogen-bonded networks based on manganese(II), nickel(II), copper(II) and zinc(II) complexes of N,N′-dimethylurea

A project related to the crystal engineering of hydrogen-bonded coordination complexes has been initiatied and some of our first results are presented here. The compounds [Mn(DMU)₆](ClO₄)₂ (1), [Ni(DMU)₆](ClO₄)₂ (2), [Cu(OClO₃)₂(DMU)₄] (3) and [Zn(DMU)₆](ClO₄)₂ (4) have all been prepared from the reaction of N,N-dimethylurea (DMU) and the appropriate hydrated metal perchlorate salt. Crystal structure determinations of the four compounds demonstrate the existence of [M(DMU)₆]²⁺ cations and ClO₄ ^– counterions in (1), (2) and (4), whereas in (3) monodentate coordination of the perchlorate groups leads to molecules. The [M(DMU)₆]²⁺ cations and ClO₄ ^– anions self-assemble to form a hydrogen-bonded one-dimensional (1D) architecture in (1) and different 2D hydrogen-bonded networks in (2) and (4). The hydrogen bonding functionalities on the molecules of (3) create a 2D structure. The complexes were also characterised by room-temperature effective magnetic moments and i.r. studies. The data are discussed in terms of the nature of bonding and the known structures.     

The vibrational spectra of complexes with planar monothio-oxamides—I. The Ni(II), Pd(II), Pt(II), Cu(II) and Zn(II) complexes of N,N′-dimethylmonothio-oxamide

The new complexes M(LH)₂ (M = Pd,Pt), ML(M = Pd,Cu) and ML · H₂O (M = Ni,Zn), where LH₂ = N,N′-dimethylmonothio-oxamide, have been prepared. The complexes were characterized by metal analyses, thermal methods and spectral (i.r., Raman, u.v.—vis.) studies. The vibrational analyses of the complexes are given using NH/ND, CH₃/CD₃ and metal isotopic substitutions. The Ni(II), Pd(II), Pt(II) and Cu(II) compounds are square planar. The monoanion LH⁻ shows a chelated bidentate S,O-coordination, while the doubly deprotonated L²⁻ acts as a bridging S,N/N,O-tetradentate ligand giving polymeric structures.     

Catalase activity of cobalt(II) complexes with N,N,N′,N′-tetrasubstituted thiocarbamoylsulfenamides

On the base of the kinetic and activation parameters of the hydrogen peroxide decomposition in the presence of chelates of CoX₂ salts (X = Cl, Br, I, NCS) with N,N,N′,N′-tetrasubstituted thiocarbamoylsulfenamides containing exocyclic (out-of-chelate) fragments of dimethylamine (I), piperidine (II), and piperazine (III) the nature of acido-ligands influence on catalase activity of complexes I–III was revealed, depending on the structure and composition of the chelating ligand. Mononuclear complexes I(Br) and II(Br) can transform into 10-membered binuclear macrochelate intermediates.     

Synthesis,characterization and SOD-like activities of manganese-containing complexes with N,N,N′,N′-tetrakis(2′-benzimidazolyl methyl)-1,2-ethanediamine (EDTB)

A series of manganese-containing mononuclear and binuclear model compounds of superoxide dismutase (SOD) coordinated by a polydentate ligand N,N,N′,N′-tetrakis(2′-benzimidazolyl methyl)-1,2-ethanediamine (EDTB) have been synthesized and characterized. The SOD-like activities of these complexes have been measured by means of modified nitroblue tetrazolium (NBT) photoreduction, and the rate constants k_Q of catalytic superoxide dismutation are in the range 6.96×10⁶–2.32×10⁷ l mol⁻¹ s⁻¹. In complex [Mn(EDTB)(Ac)](Ac)·C₂H₅OH the coordination environment around the manganese(II) ion can be described as a highly-distorted capped octahedron with an oxygen atom of the bidentate acetate ion at the capping site. This complex is the first example in which EDTB acts as a pentadentate ligand with one non-ligating benzimidazole group.     

Synthesis and magnetic properties of heterobinuclear copper(II)–iron(II) complexes with N,N′-bis(2-aminopropyl)oxamidocopper(II)

Six new -oxamido heterobinuclear complexes, namely [Cu(oxap)Fe(L)2]SO4, where oxap denotes the N,N-bis(2-aminopropyl)oxamido dianion and L represents 1,10-phenanthroline (phen); 5-nitro-1,10-phenanthroline (NO2-phen); 5-chloro-1,10-phenanthroline (Cl-phen); 5-methyl-1,10-phenanthroline (Me-phen); 2,2-bipyridine (bpy); and 4,4-dimethyl-2,2-bipyridine (Me2bpy), have been synthesized and characterized by elemental analyses, i.r. spectra, electronic spectra, magnetic moments (at room temperature) and molar conductivity measurements. The temperature dependent magnetic susceptibilities of [Cu(oxap)Fe(bpy)2]SO4 (1) and [Cu(oxap)Fe(phen)2]SO4 (2) have been studied in the 4.2–300K range, giving the exchange integrals J=–20.9cm–1 for (1) and J=–22.5cm–1 for (2). These results are commensurate with antiferromagnetic interactions between adjacent metal ions within each molecule.     

Oxamidato complexes. Part 4. Electrochemical study of the copper(III)/copper(II) couple in monomeric N,N′-bis(substituent)oxamidatocopper(II) complexes

Summary The electrochemical behaviour of a series of monomeric N,N-bis(substituent)oxamidato copper(II) complexes of formula Na₂[Cu(3,5,3,5-X₄obbz)]·4H₂O [X = Cl (1), Br (2), I (3) and obbz = oxamidobis(benzoato)], Na₂-[Cu(obbz)]·4H₂O (4), Na₂[Cu(5,5-Me₂obbz)]·4H₂O (5), Na₂[Cu(4,5,4,5-(MeO)₄obbz)]·4H₂O(6),Na₂[Cu(obp)]· 3.5H₂O (7) (obp = oxamidobis(propionato)) and Na₂[Cu(pba)]·6H₂O (8), [pba = propylenebis(oxamate)] has been investigated by cyclic voltammetry, rotating disk electrode and coulometry in water and dimethylsulphoxide (dmso) solutions. NaNO₃ (0.1 M) and n-Bu₄NPF₆ (0.1 M) were used as supporting electrolytes in H₂O and dmso respectively, all solutions being thermostatted at 25 °C. In aqueous solution, the complexes show an oxidation peak ranging from 1.19 to 0.86 V (values referred to the s.c.e.), the corresponding reduction being unobserved, even at high scan rates. In dmso, all the complexes exhibit only one oxidation peak ranging from 0.86 to 0.51 V, the corresponding reduction being observed for all of them except for (3). The oxidation potentials are strongly dependent upon the nature of the N,N-substituent of the oxamide. The copper(III)-assisted hydrolysis of the oxamidate ligand is analysed in terms of the lack of planarity of the oxamidate ligand induced by the steric effect of the halogen substituent in the 3-position on the phenyl rings. The influence of the nature of the solvent was also studied.     

The characterization of some square planar Ni(II) complexes of N,N′-ethylenebis (isonitrosoacetylacetoneimine)

The ligand (H₂L) is prepared by the condensation of 2 molecules of isonitrosoacetylacetone with 1 molecule of ethylenediamine. The dimeric nature of the ligand is compatible with the types of the square planar Ni(II) complexes it produces with NiX₂(X  Cl, NO₃, CH₃CO₂). The 1:1 up to 5:1 molar ratio reaction of nickel chloride with the ligand produced the same complex H₂LNiCl₂ · HLNiCI(I) which did not react with pyridine, while the 1:2 and 1:3 molar ratio reaction afforded the complexes LNi · HLNiCl(II) and (LNi)₂(III) respectively. The reaction of nickel nitrate with (H₂L)₂ led to the formation of the complex LNi · HLNiNO₃(IV). The Ni(II) complex LNi(V) of the monomeric ligand was obtained by either the reaction of nickel acetate with (H₂L)₂ (1:1 or 5:1) or by reacting nickel chloride with the neutral solution of the ligand (1:1 or 2:1). The two anions of the ligand are linked together through either (a) hydrogen bonding formation that involves the oxime groups (H₂L and complex I), (b) coordination of one on the oximato group of a ligand's anion with the chelated metal ion to another ligand's anion (complex III), or (c) by both types of linkages (complexes II and IV). The suggested molecular formulations are based on analytical, spectral and magnetic moment evidence.