Cation-Induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates

Cation-induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates (Ni(II)TCP, Pd(II)TCP, and Pt(II)TCP) on treatment with potassium thiocyanate in a chloroform-methanol solution has been studied by electronic absorption spectroscopy. The formation of [{MTCP}₂(K⁺)₄](SCN^?)₄ in solution induces a hypsochromic shift of the Soret band and a bathochromic shift of the β-band with respect to their positions in the spectrum of MTCP. The equilibrium constants (K) for the 2MTCP + 4K⁺ = [{MTCP}₂(K⁺)₄] processes at 20°C are determined to be as follows: log K _Ni(II)TCP = 27.31 ± 1.67, logK _Pd(II)TCP = 27.16 ± 1.43, and logK _Pt(II)TCP = 26.15 ± 1.56.     

Interaction of porphyrins with adenine and adenosine complexes. Effect of a metal nature

Reactions of complex formation of 5,10,15,20-tetraphenylporphine (H₂TPP) and tetra-tert-butylphthalocyanine (H₂(t-Bu)₄Pc) with adenine and adenosine complexes of d-metals in DMSO and ethanol are studied. It was found that H₂TPP reacts with Cu(II) and Hg(II) adeninates and adenosinates in DMSO, but does not react with Zn(II), Co(II), and Cd(II) adeninates and adenosinates (with both bridging and monodentate type of the ligand coordination). H₂(t-Bu)₄Pc enters the complex formation reaction with adeninates and adenosinates of all studied metals in DMSO at almost equal rates. The states of adenine and adenosine complexes of different d-metals in DMSO and ethanol are proposed on the basis of kinetic data obtained.     

Synthesis and X-ray diffraction studies of chiral nickel(II), zinc(II), manganese(II), and cobalt(II) complexes with C 2-symmetric 2,6-bis[4′-(R)-ethoxyoxazolin-2′-yl]pyridine

Chiral nickel(II), zinc(II), manganese(II), and cobalt(II) complexes with C ₂-symmetric 2,6-bis[4′-(R)-ethoxyoxazolin-2′-yl]pyridine were prepared, the single crystal of nickel(II) complex, [Ni((R,R)-Et-Py-box)(H₂O)₂Cl]Cl ((R,R)-Et-Pybox is 2,6-bis[4′-(R)-ethoxyoxazolin-2′-yl]pyridine), was obtained and indicated by X-ray diffraction analysis. The nickel(II) complex crystallizes in the orthorhombic system, space group P2₁2₁2₁ with a = 7.7346(4) Å, b = 19.7133(13) Å, c = 25.8014(14) Å, V = 3934.1(4) ų, Z = 8, and R = 0.0526 against 7010 reflections with I > 2σ (I). A feature of interest was noted in the unit cell of the compound, where two types of molecules exist, which similarly have a distorted octahedral geometry but only slightly differ in the orientation of the coordinated atoms to the central Ni atom. These two types of molecules interact with each other by O-H…Cl hydrogen bonds, giving rise to one dimensional ribbon structure.     

Complexes of the selected transition metal ions with 4-methoxycinnamic acid

In this study, 4-methoxycinnamates of Mn(II), Co(II), Ni(II), Cu(II), Cd(II), Nd(III) and Gd(III) were synthesised. From the infrared (IR) spectra analysis of complexes, sodium salt and according to the spectroscopic criteria the carboxylate groups seem to be bidentate chelating. The complexes of 4-methoxycinnamates lose the water molecules in one or two steps. The final products of their decomposition are oxides of the respective metals. The enthalpy values of dehydration process were determined. The FTIR spectra of the gas phase products indicate that the decomposition of the complexes is connected mainly with the release of molecules of water (H₂O), carbon dioxide (CO₂), carbon monoxide (CO), methane (CH₄) and other hydrocarbons. The analysed compounds follow the Curie?CWeiss law. The magnetic moment values experimentally determined change as follows: from 5.90??? _B to 6.27??? _B for Mn(II) complex, from 4.57??? _B to 4.99??? _B for Co(II) complex, from 3.68??? _B to 3.30??? _B for Ni(II) complex, from 1.87 ?? _B to 1.96 ?? _B for Cu(II) complex, from 3.06??? _B to 3.51??? _B for Nd(III) complex, and from 6.91??? _B to 6.90??? _B for Gd(III) complex.     

Coordination chemistry of the alkaline earth metal ions with Zwitterionic forms of the Schift bases. X-Ray studies and other spectroscopic properties

The non-ionized forms of tetradentate Schiff bases NN′-ethylenebis(salicylideneimine), H₂L and NN′-propane-1,3-diylbis(salicylideneimine), H₂L′ react with hydrated alkaline earth halide and nitrate to give complexes of the type: M(H₂L)Cl₂·nH₂O [M = Mg(II), Ca(II), Sr(II); n = 0–4], M(H₂L)₂Cl₂ [M = Ca(II), Sr(II), M(H₂L)_nBr₂ [M = Ca(II), Sr(II); n = 2, 3 and Mg₂(H₂L)₃Br₄], M(H₂L)_nI₂ [M = Mg(II), Ca(II), Sr(II), Ba(II); n = 2, 3)], M(H₂L)_n(NO₃)₂ and M(H₂L′)_n(NO₁)₂[M = Mg(II), Ca(II);n = 1, 2)]. Because of distinct spectral similarities with structurally known Ca(H₂L′)(NO₃)₂ compound, the Schiff bases are coordinated through the negatively charged phenolic oxygen atoms and not the nitrogen atoms of the azomethine groups, which carry the protons transferred from phenolic groups on complexation. Halide and nitrate are coordinated to the central metal ion except in 2:1 nitrato complexes where the presence of both ionic and coordinated nitrate groups are evident and also in 3:1 halide complexes where the presence of non-coordinated halide cannot be excluded. X-Ray powder photographs showed no marked similarities between Ca(H₂L′)(NO₃)₂ and Mg(H₂L′)(NO₃)₂ while there are some isomorphic features between the same types of halide complexes. Infrared spectra and other structural information revealed the polymeric nature of the complexes. Therefore the coordination numbers exhibited by the alkaline earth metal cations would be 4, 6 or 8 in these series of Schiff base complexes.     

Studies on the intermolecular interactions of metal chelate complexesVIII: On the interactions of dithiocarbamato-copper(II) and -copper(I) complexes with haloalkanes

The interaction of Cu(II)(dtc)₂ and Cu(I)(dtc) complexes with haloalkanes were studied by the EPR method. It was found that the Cu(II)(dtc)₂ complex reacted with haloalkanes only in the presence of weak Lewis bases which formed adducts with it. The intermediate reaction product is the mixed-ligand complex Cu(II)(dtc)X_n (X = Cl, Br, n = 1 or 2); the final products being CuX₂B_n (B = Lewis bases, n = 1 or 2) and unstable resin-like residue. Cu(I)(dtc) reacted with haloalkanes without any promoters giving the mixed-ligand complex Cu(II)(dtc)X_n as product. Free radicals were detected in the reaction of Cu(I)(dtc) using the method of “radical scavenger” and were not found in the reaction of Cu(II)(dtc)₂. The reported results confirmed one of the two reaction mechanisms proposed in the previous studies. The role of the solvent on the EPR parameters of the mixed-ligand Cu(II)(dtc)X complex is also discussed.     

Thermal decomposition reactions of metal carboxylato complexes in the solid state. I.: Thermographic and differential thermal studies of metal oxalato,malonato and succinato complexes

Thermal investigation of metal carboxylato complexes of the first transition metals, Mn(II), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) and non-transition metals like Zn(II) and Cd(II) in the solid state has been carried out under non-isothermal conditions in nitrogen atmosphere by simultaneous TG and DTA. TG and DTA curves inferred that the thermal stability of the complex decreased approximately with the increase of the standard potential of the central metal ion. The thermal parameters like activation energy, E_a, enthalpy change, ΔH, and entropy change, ΔS, corresponding to the dehydration and decomposition of the complexes are determined from TG and DTA curves by standard methods. A linear correlation is found between ΔH and ΔS and E_a and ΔS in dehydration and decomposition processes. DTA curves show an irreversible phase transition for Na₂Mn(mal)₂], Na₂[Cu(mal)₂] and Na₂,[Co(suc)₂] complexes. The residual products in these decomposition processes being a mixture of two oxides, of oxide and carbonate or a mixture of two carbonates.     

Thermal decomposition reactions of metal carboxylato complexes in the solid state: II. Thermographic and differential thermal studies of metal oxalato,malonato and succinato complexes

The thermal investigations of metal carboxylato complexes of the first transition metals, Mn(II), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) and non transition metals like Zn(II) and Cd(II) in solid state were carried out under non-isothermal condition in nitrogen atmopshere by thermogravimetric (TG) and differential thermal analyses (DTA) methods. The results of DTA curves inferred that the thermal stability of the complex decreased approximately with the increase of standard potential of the central metal ion. The thermal parameters like activation energy (E_a¹), enthalpy change (ΔH) and entropy change (ΔS) corresponding to deaquation, deammoniation and decomposition processes occurred simultaneously or separately were determined from TG and DTA curves by the standard methods. A linear correlation has been found in the plots of ΔH vs. ΔS and E_a¹ vs. ΔS in deaquation, deammoniation and decomposition processes. An irreversible phase transition was noticed for H₂[Mn(suc)₂] and H₂[Co(suc)₂] complexes in DTA curves. The residual pyrolysed products were metal carbonates.     

Thermodynamics,formation constants,spectrophotometry and infrared spectroscopy of complexes between some divalent metal ions and 3-hydrazino-6-phenylpyridazine and related ligands

The stepwise formation constants of complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Cd(II) and UO₂(II) ions with 3-hydrazino-6-phenylpyridazine (HPP) and its condensation products with benzil (BHPP) and p-methoxyacetophenone (p-MeOAHPP) were determined in a 75% (v/v) dioxane-water mixture at μ = 0.05 M (KNC₃). The effect of temperature (at 10, 20, 30 and 40 °C) was also examined for Cu(II) and UO₂(II)-BHPP complexes. The overall changes in ΔG, ΔH and ΔS have been calculated. The solid complexes of Cu(II)-, Co(II)- and Ni(II)-BHPP were prepared and examined by elemental analysis and IR spectroscopy. Analysis of the data indicates chelation of the BHPP ligand through the nitrogens of both hydrazone and the pyridazine ring and the carbonyl oxygen group. The spectrophotometric studies were performed on solutions of Cu(II), Ni(II) and Co(II) with BHPP in order to obtain the optimum pH values for complex formation. The compositions of the chelates formed were determined. Analytical determinations of the micro amounts of Cu(II), Ni(II) and Co(II) were also done using BHPP as the complexing agent.     

The influence of ms-substitution on the properties of 3,3′-bis(dipyrrolylmethenes) and their coordination compounds

We have compared the coordination properties of decamethyl-substituted 3,3′-bis-(dipyrrolylmethenes) (H₂L) with different ms-spacers separating the dipyrrolylmethene domains: methylene -CH₂-, methoxyphenylmethylene -CH(p-C₆H₄OMe)-, and trifluoromethylmethylene -CH(CF₃)-. The stable binuclear homoligand complexes [M₂L₂] are formed in reactions of the ligands with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates. In the cases of all H₂L ligands the thermodynamic constants of the complex formation reactions increase in the following series: Cu(II) < Cd(II) < Hg(II) < Ni(II) < Co(II) < Zn(II). The change in -CH₂- ms-spacer to -CH(p-C₆H₄OMe)- or -CH(CF₃)- results in a decrease in the constant of H₂L complex formation by 1–4 orders of magnitude, the cation being the same. The influence of ms-substitution on the stability and luminescence properties of [M₂L₂] has been discussed.     

Complexation en solution aqueuse des ions magnesium(II), manganese(II), nickel(II), cuivre(II) et plomb(II) avec la s-carboxymethyl-l-cysteine: Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution

Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution.The complex formation between Mg(II), Mn(II), Ni(II). Cu(II), Pb(II) ions and S-carboxy-methyl-l-cysteine (H₂A) has been studied by measurement of pH at 25°C and constant ionic strength (1 M NaClO₄). Although no interaction occurs with Mg(II), this work provides evidence for a variety of complexes: MnA; CuHA⁺; CuA; CuA₂^2-; NiHA⁺; NiA; NiA₂^2-; PbHA⁺; PbA et PbA(OH)^-. The overall formation constants of all these species are computed and refined. The results allow the determination of the distribution of the complexes as a function of pH; some structural features of the metal complexes in solution are indicated.     

Estimation of stability constants of copper(II) and nickel(II) chelates with dipeptides by using topological indices

The estimation of the overall stability constants β₁ of copper(II) and nickel(II) chelates with dipeptides was performed by using the model with the valence connectivity index of the 3rd order (³χ^v). It was done by dividing β₁ to its constituting constants K₁ and K_a, and subsequently by dividing the basic set into subsets or treating the chelate rings as separate units. Altogether 15 copper(II) and eight nickel(II) chelates with dipeptides were investigated. Six models for the estimation of log K₁ and pK_a were checked, most of them by usage of indicator variables (for differentiation of copper(II) and nickel(II) complexes or subclasses of ligands). Estimates of log β₁ gave the range of rms values from 0.19 to 0.27. For the best model, errors of estimates were less than 0.34.     

Synthesis,crystal structure,spectral and biological studies of Cu–M(M = Zn and Pb) heterodinuclear complexes of new phenol-based macrocyclic ligands

Eight new heterodinuclear Cu(II)–M(II) (M = Pb and Zn) complexes of four new phenol based compartmental macrocyclic ligands, possessing contiguous (N₂O₂) and (N_xO₂) (x = 2, 3) coordination sites, were prepared by the template reaction of [N,N′-bis(3-formyl-5-methylsalicylidene)ethane-1,2-diaminato]copper(II), with various di- and/or tri-amines in the presence of Pb(II) and Zn(II) ions. The crystal structure of [CuZnL³(H₂O)](ClO₄)₂, 6, was determined by X-ray diffraction and shows that the Zn(II) and Cu(II) ions reside in the N₂O₂ sites of the macrocyclic ligand. The fifth coordination site of the Zn centre is occupied by a water ligand. All the complexes have been characterized by elemental analysis, molar conductivity and spectroscopic methods (IR and UV). Also, all the synthesized complexes were screened for their antibacterial and antifungal activity against Escherichia coli, Staphyloccocus aureus and Candida albicans.     

Substituted benzeneseleninic acids as bidentate ligands. Synthesis and spectroscopic studies of manganese(II) and iron(II) complexes

The para- and meta-substituted seleninato anion, XC₆H₄SeO⁻₂, forms complexes with manganese(II) and iron(II) of the type [M(XC₆H₄SeO₂)₂(H₂O)₂], which have been shown to contain the bidentate ligand in seleninato-_O, O′ derivatives, the water molecules being coordinated to the metals. From the electronic absorption spectra and from the magnetic susceptibility data we have proposed for all the complexes a distorted octahedral D_4h symmetry. The structure of the anhydrous para- and meta-substituted benzeneseleninato complexes of manganese(II) and iron(II) have been investigated by means of electrical conductance measurements, spectral (electronic and i.r.) studies and magnetic susceptibility measurements. The anhydrous complexes are always of the seleninato-O, O′ type with the ligands tetrahedrally coordinated to the central atom. The wavelengths of the principal absorption peaks have been accounted for quantitatively in terms of the crystal field theory for manganese(II) derivatives. The nephelauxetic parameters are all indicative of an appreciable metal-ligand covalency.     

Anderson-type heteropolyanions of molybdenum(VI) and tungsten(VI)

The previously reported preparation of some Anderson-type molybdopolyanions containing divalent metal ions (Zn, Cu, Co or Mn) as a heteroatom has been reinvestigated. The molybdopolyanions of Zn(II) and Cu(II) were confirmed, although the Cu(II) polyanion was not stable and could not be recrystallized. On the other hand, the polyanions of Co(II) and Mn(II) could not be reproduced. Another type of heteropoly compound, [X(H₂O)_6-x(Mo₇O₂₄)]⁴⁻ [X = Cu(II), Co(II) or Mn(II)], was isolated as solids, which are not stable thermally. The mixed-type Anderson polyanions, [Ni(II)Mo_6-xW_x,O₂₄H₆]⁴⁻, which have been questioned as mixtures of species with different x values, were also reinvestigated using IR, UV absorption and MCD spectra. They are single species, but not mixtures, although some positional isomers may be present for the compounds where x = 2-4. The possibility of oxidation of the heteroatom with the Anderson structure maintained was examined. The oxidation of [Ni(II)Mo₆O₂₄H₆]⁴⁻ by the S₂O²⁻₈ ion in aqueous solution gave the Waugh-type [Ni(IV)Mo₉O₃₂]⁶⁻ polyanion, whereas the oxidation of [Ni(II)W₆O₂₄H₆]⁴⁻ gave no heteropoly compound.     

Thermal decomposition of some metal chelates of substituted hydrazopyrazolones

The thermal dissociation of 1-phenyl-3-methyl-4-(X-phenylhydrazo)-5-pyrazolone metal chelates [M(XPhHyPy)](X=m-OH (I),m-OCH₃(II),m-COOH (III),p-CH₃ (IV),p-OCH₃ (V) orp-COCH₃ (VI) was studied by TG, DTG and differential thermal analysis (DTA). A rough sequence of thermal stability, obtained from the peak maximum temperatures, for the various metal chelates was Hg(II)2(II). The bonding of the ligands to metal ions was investigated by elemental analysis and infrared spectroscopy. The number and relative energies of nitrate combiantion frequencies are discussed in terms of the complexation of para-substituted hydrazopyrazolone with Th(IV) and UO₂(II) metal ions.     

Synthesis and characterization of Cu,Ni and Zn binding capability of some amino- and imidazole hydroxamic acids: Effects of substitution of side chain amino-N for imidazole-N or hydroxamic-N-H for -N-CH3 on metal complexation

Solution equilibrium studies on Cu(II)-, Ni(II)- and Zn(II)-N-Me-β-Alaninehydroxamic acid (N-Me-β-Alaha), -N-Me-α-alaninehydroxamic acid (N-Me-α-Alaha), -Imidazole-4-carbohydroxamic acid (Im-4-Cha), -N-Me-imidazole-4-carbohydroxamic acid (N-Me-Im-4-Cha) and -Imidazole-4-acetohydroxamic acid (Im-4-Aha) systems have been performed by pH-potentiometry, UV–Vis spectrophotometry, EPR, CD, ESI-MS and ¹H NMR methods. According to the results: (i) the amino-N atoms are more basic in N-Me-α-Alaha and N-Me-β-Alaha than the hydroxamate function, but the trend is just the opposite between the imidazole-N(3) and hydroxamate. (ii) The metal ion anchor is always the hydroxamate part in the amino acid derivatives, while it is always the imidazole-N(3) in the studied imidazolehydroxamic acids. (iii) The three studied N-Me derivatives do not form metallacrowns. Only hydroxamate type chelate is formed with N-Me-β-Alaha, but with N-Me-α-Alaha a new type of coordination mode (via amino-N and hydroxamate-O) also exists. N-Me-Im-4-Cha also forms a dinuclear complex, [M₂L₃], with Cu(II) and Ni(II) (but not with Zn(II)). In this complex, one of the three ligands might bridge the two metal ions (five-membered hydroxamate-(O,O) plus five-membered (N_im, O_carb) bridging bis-chelating mode), while each of the additional two ligands binds to one metal. (iv) The two studied N–H derivatives, having dissociable proton on the hydroxamic-N, are able to form metallacrown species. A pentanuclear complex, [M₅L₄H₋₄], is exclusively formed above pH 4 between Cu(II) and Im-4-Aha. Interestingly, this 12-metallacrown-4 type complex, although together with various mononuclear binding isomers, appears also with Ni(II) and Zn(II). Unfortunately, the complexes of Im-4-Cha are not soluble in water at physiological pH at all.     

Infrared spectral studies on the stability of some binuclear transition metal—Schiff base complexes

Some di-Schiff bases like N,N′-o-phenylene-bis-salicylaldimine (DSB₁), N,N′-m-phenylene-bis-salicylaldimine (DSB₂) and N,N′-p-phenylene-bis-salicylaldimine (DSB₃) have been synthesized by the condensation of salicylaldehyde with o-, m- and p-phenylenediamines, respectively. The synthesized complexes of Cu(II), Ni(II) and Co(II) with these ligands have been assigned their molecular structure on the basis of their elemental analyses, molecular weight determination, magnetic measurements, electronic spectra, molar volume and infrared spectral studies. The nature of bonding between metal ion and Schiff bases is studied by i.r. spectrophotometry. The shift in the band position of the groups involved in coordination has been utilized to estimate the coordination bond lengths. The value of the coordination bond length of Cu(II) complexes is shorter than the corresponding values for Ni(II) and Co(II) complexes.     

Mössbauer spectroscopic studies of molecule-based magnets: NBu4[Fe(II) x Mn(II)1-x Cr(III)(ox)3] and NBu4[Fe(II) x Ni(II)1-x Fe(III)(ox)3]

The internal magnetic field (H _n ) at⁵⁷Fe nucleus was investigated for the mixed crystals, NBu₄[Fe(II) _x Mn(II)_1-x Cr(III) (ox)₃] (x=0.03?1) and NBu₄[Fe(II) _x Ni(II)_1-x Fe(III)(ox)₃]) (x=0?1) using Mössbauer spectroscopy, where NBu₄/⁺=tetra(n-butyl)ammonium ion and ox^2?=oxalate ion. With the decrease ofx, the direction ofH _n at Fe(II) in NBu₄[Fe(II) _x Mn(II)_1-x Cr(III)(ox)₃] changed gradually from parallel to perpendicular, to the honeycomb layers consisting of an alternate array of the bivalent and tervalent ions through ox^2? ligands. A variation of ca. 50° in direction was observed for theH _n at Fe(III) in NBu₄[Fe(II) _x Ni(II)_1-x Fe(III)(ox)₃].     

Ethoxyacetylene: A useful building block for the organocopper(I) mediated synthesis of 1,4-diketones

Ethoxyacetylene (I) has been converted by organocopper(I) species into (E)-2-ethoxy-1-alkenylcopper(I) compounds (II). The adducts II have been shown to be useful intermediates for preparation of 1,4-diketones (VI). Two routes to VI were used: (i) sequential treatment of II with allyl bromide, 3.0 N HCl, and PdCl₂/CuCl in DMF/H₂O, and (ii) sequential treatment of II with 2,3-dibromopropene and Hg(OAc)₂. A dienone was formed from the first procedure when after the reaction of II with allyl bromide the product was treated first with the PdCl₂/CuCl.