Spectrochemical Properties of Noncubical Transition Metal Complexes in Solutions. IX. The Mixed Tetragonal Distorted Bis(Salicylato)Cobalt(II) Complex in Various Solvents

Mixed cobalt(II) complexes with the monodentate ligands: 2-hydroxybenzoic acid deprotonated (sal^–, the salicylate ion) and water, have been investigated. The combined results of the spectrophotometric and conductance measurements, as well as known the X-ray structure for solids, were used to determine the structure of the studied complexes in solution. The electronic absorption spectra in aqueous acid (0.01M HClO₄), ethylene glycol (glycol), formamide (FM), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) solutions have been recorded. The d-d electronic spectra have been treated by the crystal-field model (CFM) and angular overlap model (AOM). Low-symmetry splittings of the broad asymmetric bands in the experimental spectra (solutions at room temperature) were found by Gaussian analysis. The effect of the and bonding of the monodentate ligands (with oxygen-donor ligators) on the central metal ion was described in the ligand–field framework. A comparison of the stereochemistry of the complex species in various solutions was made.     

Thermal Studies of Cobalt(II), Nickel(II) and Copper(II) Complexes of 4-(Sulfonylazido Phenylazo) Pyrazolones

The thermal decompositions of cobalt(II), nickel(II) and copper(II) complexes of4-(3'-sulfonylazido-6'-methoxyphenylazo)-1-phenyl-3-methyl-2-pyrazolin-5-one H(D¹–SO₂N₃) and 4-(4'-sulfonylazido phenylazo)-3-phenyl-3-methyl-2-pyrazolin-5-one H(D²–SO₂N₃) were studied by thermogravimetry. The decomposition in all cases takes place along two stages. The first stage is due to the elimination of water and nitrogen molecules with the formation of tetracoordinate complexes containing nitrene reactive species[M(DSO₂N:)₂]. The second stage represents the decomposition of the material to the metal oxide. The kinetics of the decomposition were examined by using Coats–Redfern, the decomposition in all complexes was found to be first order for the first and second stages. The activation energies and other activation parameters (H^* and S^* and G^*) were computed and related to the bonding and stereochemistry of the complexes.This revised version was published online in November 2005 with corrections to the Cover Date.     

Complex formation between nickel(II) and 2-(2-aminoethyl) benzimidazole: A kinetic and equilibrium study

Summary The reversible complex formation between 2-(2-aminoethyl) benzimidazole (AEB) and nickel(II) was studied by stopped flow spectrophotometry at I = 0.30 mol dm^–3. Both the neutral and monoprotonated form of AEB reacted to give the NiAEB²⁺ chelate. At 25 °C, the rates and activation parameters for the reactions Ni_II + AEB NiAEB²⁺ and Ni^II + AEBH⁺ NiAEB²⁺ + H⁺ are k _f ^L(dm^–3 mol^–1 s^–1) = (2.17 ± 0.24) × 10³, H (kJ mol^–1) = 40.0 ± 0.8, S (JK^–1 mol^–1) = – 47 ± 3 and k _inff ^pHL (dm³ mol^–1 s^–1) = 33 ± 10, H (kJ mol^–1) = 42.0 ±2.7, S (JK^–1 mol^–1) = – 72 ± 9. The dissociation of NiAEB²⁺ was acid catalysed and k _obs for this process increased linearly with [H⁺] in the 0.01–0.15 mol dm^–3 (10–30 °C) range with k _H(dm³ mol^–1s^–1) (25 °C) = 329 ± 6, H (kJ mol^–1) = 40 ± 2 and S (JK^–1 mol^–1) = – 61 ± 8. The results also indicated that the formation of NiAEB²⁺ involves a chelation-controlled, rate-limiting process. Analysis of the S ° data for the acid ionisation of AEBH _inf2 ^p2+ and the formation of NiAEB²⁺ showed that the bulky AEBH⁺ ion has a solvent structure breaking effect as compared to AEB [s _aqS ° (AEBH⁺) – s _aq ° (AEB) = 69 JK^–1 mol^–1], while AEBH _inf2 ^p2+ is a solvent ordering ion relative to NiAEB²⁺ [s _aq° (NiAEB²⁺) – ovS _aq ° (AEBH _inf2 ^p2+ ) = 11 JK^–1 mol^–1].Author to whom all correspondence should be directed.     

Structural studies of diamine complexes of cobalt(II) and nickel(II) thiocyanates and selenocyanates

Summary Complexes of the types ML₂X₂ [M = cobalt(II) or nickel(II); L = hydrazine, ethylenediamine (en) or o-phenylenediamine (opd) and X = SCN^– or SeCN^–] and NiL₂(NCS)₂MCl₂ [M = cadmium(II) or mercury(II)] have been prepared and characterised by elemental analysis, molar conductance, molecular weight determination, magnetic susceptibility, electronic and i.r. spectral measurements.     

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.     

Chromium(VI), chromium(V) and chromium(IV) oxidation of 12-tungstocobaltate(II)

The reaction between Cr^VI and 12-tungstocobaltate(II) was carried out in 2.0 mol dm^–3 HCl and followed a simple second order rate law. The reaction was catalysed by hydrogen ion due to the formation of active H₂CrO₄ and was inhibited by chloride ion as, in its presence, conversion of the active species into inactive chlorochromate occurs. Chromium(V) and chromium(IV) were generated in situ by the use of Cr^VI—V^IV or Cr^VI—2-ethyl-2-hydroxybutyric acid and Cr^VI—i-PrOH reactions respectively, and the oxidation of 12-tungstocobaltate(II) by these atypical oxidation states, was also studied. The rate constants for the oxidation of 12-tungstocobaltate(II) by Cr^VI, Cr^V and Cr^IV were found to be in the ratio 1:1.2:5.2 respectively. The ionic strength did not affect the reaction, while decrease in the solvent polarity increased the rate of the reaction. The activation parameters were also determined and the values H , G and S were found to be 52.4 ± 6 kJ mol^–1, 100.8 ± 7 kJ mol^–1, –151.7 ± 10 J K^–1 mol^–1 respectively, supporting the mechanism proposed.     

Cobalt(II), nickel(II) and copper(II) complexes of 1-hydroxy-2-naphthyl(4-X-styryl)ketones

Summary Metal(II) bis-chelates of the type ML₂nB [M=Co^II, Ni^II, and Cu^II, L=1-hydroxy-2-naphthyl(4-X-styryl)ketone, (X=H, Me, Cl, MeO), B=H₂O, Py; n=0, 2] have been prepared and characterised by element analyses, i.r., ligand field spectra, magnetic moments and thermal studies. The copper(II) chelates are anhydrous monomers oftrans-square-planar configuration. The cobalt(II) and nickel(II) chelates, obtained as dihydrates, possess a high-spintrans-octahedral structure. Their anhydrides are polymeric. All the pyridine adducts have high-spintrans-octahedral geometry. The (M–O), order, namely Cu >Ni>Co, parallels the Irving-Williams order. The weak ligand field strength of 1-hydroxy-2-naphthyl(4-X-styryl)ketones is ascribed to inhibition of extensive conjugation arising from deviation of the naphthoyl group from planarity.     

Kinetics and mechanism of formation and dissociation of copper(II) and nickel(II) complexes of the Schiff base bis(acetylacetone)ethylenediimine in aqueous-organic solvent media

Summary In NH₄NO₃+NH₄OH buffered 10% (v/v) dioxan-water media (pH 7.0–8.5), thePseudo-first-order rate constant for the formation of the title complexes M(baen),i.e. ML, conforms to the equation 1/k_obs=1/k+1/(kK_o.s · T_L), where T_L stands for the total ligand concentration in the solution, K_o.s is the equilibrium constant for the formation of an intermediate outer sphere complex and k is the rate constant for the formation of the complex ML from the intermediate. Under the experimental conditions the free ligand (pK_a>14) exists virtually exclusively in the undissociated form (baenH₂ or LH₂) which is present mostly as a keto-amine in the internally hydrogen-bonded state. Although the observed formation-rate ratio k^Cu/k^Ni is of the order of 10⁵, as expected for systems having normal behaviour, the individual rate constants are very low (at 25°C, k^Cu=50 s^–1 and k^Ni=4.7×10^–4s^–1) due to the highly negative S values (–84.2±3.3 JK^–1M^–1 for CuL and –105.8±4.1 JK^–1M^–1 for NiL); the much slower rate of formation of the nickel(II) complex is due to higher H value (41.2±1.0 kJM^–1 for CuL and 78.2±1.2 kJM^–1 for NiL) and more negative S value compared to that of CuL. The K_o.s values are much higher than expected for simple outer-sphere association between [M(H₂O)₆] and LH₂ and may be due to hydrogen bonding interaction.In acid media ([H⁺], 0.01–0.04 M) these complexes M(baen) dissociate very rapidly into the [M(H₂O)₆]²⁺ species and baenH₂, followed by a much slower hydrolytic cleavage of the ligand into its components,viz. acetylacetone and ethylenediamine (protonated). For the dissociation of the complexes k_obs=k₁[H⁺]+k₂[H⁺]². The reactions have been studied in 10% (v/v) dioxan-water media and also ethanolwater media of varying ethanol content (10–25% v/v) and the results are in conformity with a solvent-assisted dissociativeinterchange mechanism involving the protonated complexes.     

Copper(II), nickel(II) and cobalt(III) complexes of the macrocyclic ligand C-meso-7,14-diphenyl-5,6-butano-12,13-butano-1,4,8,11-tetraazacyclotetradeca-4,11-diene

Summary Metal complexes of the macrocyclic tetraaza ligand C-meso-7,14-diphenyl-5,6-butano-12,13-butano-1,4,8,11-tetraazacyclotetradeca-4,11-diene (L) are described. The copper(II) and nickel(II) complexes, isolated as their perchlorate salts, are 4-coordinate species. Several cobalt(III) complexes,trans-[CoLX₂]⁺(X = Cl^–, Br^–, NO ₂ ^– or N ₃ ^– have also been characterised. The most probable stereochemistry of the ligand in the metal complexes is the C-meso-N-meso arrangements of the chiral centres. The N-meso stereochemistry leads to the bulky phenyl groups lying in equatorial positions. I.r. and d-d spectra are reported for the various complexes described.     

Copper(II) halide reactions with the - NH · CS - group in heterocyclic pentaatomic rings

Summary White crystalline complexes of general formula Cu₂L₄X₂ (where X = Cl, Br and L = 1, 3-oxazolidine-2-thione, pyrrolidine-2-thione,N-methyl-1,3-imidazolidine-2-thione andN-ethyl-1,3-imidazolidine-2-thione) and CuLX (where L = 1,3-imidazolidine-2-thione) were prepared by reduction of copper(II) halides and studied by i.r. spectroscopy in the 4000–200 cm^– range. Evidence for ligand coordination to the metal through sulphur was found in each case. The(CuCI) vibration in all the chloro derivatives falls atca. 240 cm^–.     

Nickel(II) and Cobalt(II) Complexes with Products of Condensation of 1-Aminonaphthalene, 2-Aminonaphthalenesulfonic-5 Acid,and Aromatic Carbinols

Seven new cobalt(II) and nickel(II) complexes with Schiff's bases were synthesized. The Schiff's bases were prepared by the condensation of 1-aminonaphthalene with carbinols, -hydroxy--phenylacetophenone (L¹), salicylaldehyde (L²), and 2-hydroxy-1-naphthaldehyde (L³), and of 2-aminonaphthalenesulfonic-5 acid with 2-hydroxy-1-naphthaldehyde (L⁴). The compounds were studied by X-ray powder diffraction, thermogravimetry, measurements of magnetic susceptibility, and spectroscopy (IR and diffuse reflectance). The coordination sites of the ligand and their dentate members were determined. A coordination number of four was realized in the Ni(II) and Co(II) complexes with L¹–L³, and the complexes with L⁴ were characterized by a coordination number of six (a dimer with an octahedral environment of each central ion).     

Studies of artificial hydrolytic metalloenzymes: The catalyzed carboxyester hydrolysis by copper(II), zinc(II) and cobalt(II) complexes of the tripod ligand tris(2-benzimidazylmethyl)amine

The hydrolysis kinetics of p-nitrophenyl acetate (NA) catalyzed by Cu^II, Zn^II and Co^II complexes of tris(2-benzimidazylmethyl)amine (NBT) have been studied. The hydrolysis rate is first-order in both metal(II) complex and NA. The second-order rate constants, k_cat are 0.083, 0.241 and 0.285mol^–1Ls^–1 (298K, I = 0.10molL^–1 KNO₃, 0.02molL^–1 tris buffer, 40% MeCN aqueous solution) for Zn–NBT, Co–NBT and Cu–NBT complexes, respectively. The result indicates that the hydrolytic metalloenzyme activity of different metal complexes increases with the electrophilicity of the metal ions and that the complexes, in this paper, constitute that most efficient hydrolytic metalloenzyme models reported to date. An increase in MeCN content in the solution greatly reduces the hydrolytic activity of the nucleophiles.     

Zinc(II) Hydration in Aqueous Solution: A Raman Spectroscopic Investigation and An ab initio Molecular Orbital Study of Zinc(II) Water Clusters

Raman spectra of aqueous Zn(II)–perchlorate solutions were measured over broad concentration (0.50–3.54 mol-L^–1) and temperature (25–120°C) ranges. The weak polarized band at 390 cm^–1 and two depolarized modes at 270 and 214 cm^–1 have been assigned to ₁(a _1g), ₂(e _g), and ₅(f _2g) of the zinc–hexaaqua ion. The infrared-active mode at 365 cm^–1 has been assigned to ₃(f _1u). The vibrational analysis of the species [Zn(OH₂) ₂ ⁺ ] was done on the basis of O _h symmetry (OH₂ as point mass). The polarized mode ₁(a _1g)-ZnO₆ has been followed over the full temperature range and band parameters (band maximum, full width at half height, and intensity) have been examined. The position of the ₁(a _1g)-ZnO₆ mode shifts only about 4 cm^–1 to lower frequencies and broadens by about 32 cm^–1 for a 95°C temperature increase. The Raman spectroscopic data suggest that the hexaaqua–Zn(II) ion is thermodynamically stable in perchlorate solution over the temperature and concentration range measured. These findings are in contrast to ZnSO₄ solutions, recently measured by one of us, where sulfate replaces a water molecule of the first hydration sphere. Ab initio geometry optimizations and frequency calculations of [Zn(OH₂) ₂ ⁺ ] were carried out at the Hartree–Fock and second-order Møller–Plesset levels of theory, using various basis sets up to 6-31 + G*. The global minimum structure of the hexaaqua–Zn(II) species corresponds with symmetry T _h. The unscaled vibrational frequencies of the [Zn(OH₂) ₂ ⁺ ] are reported. The unscaled vibrational frequencies of the ZnO₆, unit are lower than the experimental frequencies (ca. 15%), but scaling the frequencies reproduces the measured frequencies. The theoretical binding enthalpy for [Zn(OH₂) ₂ ⁺ ] was calculated and accounts for ca. 66% of the experimental single-ion hydration enthalpy for Zn(II).Ab initio geometry optimizations and frequency calculations are also reported for a [Zn(OH₂) ₂ ¹⁸ ] (Zn[6 + 12]) cluster with 6 water molecules in the first sphere and 12 in the second sphere. The global minimum corresponds with T symmetry. Calculated frequencies of the zinc [6 + 12] cluster correspond well with the observed frequencies in solution. The ₁-ZnO₆ (unscaled) mode occurs at 388 cm^–1 almost in perfect correspondence to the experimental value. The theoretical binding enthalpy for [Zn(OH₂) ₂ ¹⁸ ] was calculated and is very close to the experimental single ion-hydration enthalpy for Zn(II). The water molecules of the first sphere form strong hydrogen bonds with water molecules in the second hydration shell because of the strong polarizing effect of the Zn(II) ion. The importance of the second hydration sphere is discussed.     

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.     

Reactivity of pyrrole pigments,XXI: Structure and reactivity of Cu(II) and Zn(II) bilindione chelates

Summary Several Mn, Cu, and Zn chelates of etiobiliverdin-IV-, mesobiliverdin-IX, and its dimethyl ester are studied. The results show that the chemical constitution of the Cu biliverdin chelate corresponds to a formal metal oxidation state of (II) coordinated to a neutral radical of the NH trideprotonated biliverdin. The reactivity of the Cu(II) bilindione chelates in nucleophilic solvents agrees with that expected for a neutral radical structure of the ligand; in CH₃OH, they undergo oxidation towards dimethoxybilipurpurins. The magnetic behaviour of Cu(II) etiobiliverdinate-IV- in the solid state shows an intramolecular weak antiferromagnetic coupling d⁹Cu-to--radical (J=–23 cm^–1) and an intermolecular weak antiferromagnetic coupling -radical-to--radical (J=–45 cm^–1). The analogy of this magnetic behaviour to that of the cation radical of metalloporphyrins is discussed.

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Reaktivität von Pyrrolpigmenten, 21. Mitt.: Struktur und Reaktivität von Cu(II)- und Zn(II)-Chelaten von Bilindionen

Zusammenfassung Einige Mn, Cu and Zn Chelate von Etiobiliverdin-IV-, Mesobiliverdin-IX und seinem Dimethylester werden untersucht. Im Komplex koordiniert ein Metallatom (mit der Formalladung II) mit einem Neutralradikal des dreifach NH-deprotonierten Bilindions. Die Reaktivität des Komplexes gegenüber nukleophilen Lösungmitteln entspricht erwartungsgemäß dem eines neutralen -Radikals; in CH₃OH wird er zu Dimethoxybilipurpurin oxidiert. Bei Cu(II)-Etiobiliverdinat-IV beobachtet man im festen Zustand neben schwacher, antiferromagnetischer Kupplung zwischen d⁹Cu und -Radikal (J=–23 cm^–1) auch eine schwache, intermolekulare, antiferromagnetische Wechselwirkung zwischen zwei -Radikalen (J=–45 cm^–1). Dieses magnetische Verhalten wird dem des -Kationradikals von Metalloporphyrinen gegenübergestellt.

     

Determination of copper(I)-ethylene complexes, [Cu(C2H4)]+ and [Cu(C2H4)2]+, with aid of EDTA titration of copper(I) and copper(II) ions

Summary Volumetric measurements of ethylene and simple EDTA titration of copper(I) and copper(II) ions confirm that [CuL]⁺ and [CuL₂]⁺ are formed when an aqueous solution of copper(II) is reduced by copper metal in the presence of ethylene, (L). The formation constants,K ₁=[CuL⁺]²[Cu²⁺]^–1[L]^–2 andK ₂=[CuL ₂ ⁺ ]^–1[L]^–1, have been estimated. The formation of [CuL]⁺ is accompanied by an enthalpy change, H, of –25 kJ mol^–1, and a positive entropy change, S, of 13 J mol^–1 K^–1.     

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.     

Spectrophotometric study of thiocyanato complexation of cobalt(II) and nickel(II) ions in micellar solutions of a nonionic surfactant triton X-100

Complexation of cobalt(II) and nickel(II) with thiocyanate ions has been studied by precise spectrophotometry in aqueous and micellar solutions of a nonionic surfactant Triton X-100 of varying concentrations (20–100 mmol-dm^–3). With regard to cobalt(II), the formation of [Co(NCS)]⁺, [Co(NCS)₂], and [Co(NCS)₄]^2– was established. The formation constant of [Co(NCS)₄]^2–, is increased with increasing concentration of the surfactant, suggesting that the [Co(NCS)₄]^2– complex is formed in micelles. In contrast, the formation constants of [Co(NCS)]⁺ and [Co(NCS)₂] are remained practically unchanged. On the other hand, with nickel(II), the formation of sole [Ni(NCS)]⁺ and [Ni(NCS)₂] was established in both aqueous and micellar solutions examined, their formation constants being also remained unchanged. Interestingly, no higher complex was confirmed in the nickel(II) system, unlike cobalt(II). The unusual affinity of the [Co(NCS)₄]^2– complex with micelles will be discussed from thermodynamic and structural points of view.     

Synthesis and characterization of cobalt(II), nickel(II), copper(II) and zinc(II) complexes with acetylacetone bis-benzoylhydrazone and acetylacetone bis-isonicotinoylhydrazone

Summary Acetylacetone bis-benzoylhydrazone (PhCONHN=CMe)₂ CH₂(LH₂) and acetylacetone bis-isonicotinoylhydrazone (NC₅H₄CONHN=CMe)₂CH₂(LH₂) complexes of the types [ML] and [ML] (M = Co^II, Ni^II, Cu^II or Zn^II) have been prepared and characterized. All the complexes are non-electrolytes and the cobalt(II) complexes are lowspin, the nickel(II) complexes are diamagnetic and the copper(II) complexes are paramagnetic. The ligands chelate via two C=N groups and two deprotonated enolate groups. The e.s.r. spectra of the copper(II) complexes indicate a tetragonally distorted dimeric structure. The X-ray diffraction parameters for [CoL] and [NiL] correspond to a tetragonal crystal lattice.     

Complexes of 1,8-bis(2-pyridyl)-3,6-dithiaoctane with cobalt(II) halides

Summary Several cobalt(II) halide complexes derived from 1,8-bis(2-pyridyl)-3,6-dithiaoctane (bpdto) are described. Chemical analysis suggests their formulae to be: Co(bpdto)X₂ (X=Cl^–, Br^–, or I^–). Electrolytic conductivities in acetonitrile, magnetic moments at different temperatures, solid state i.r. and u.v.-visible spectra support a tetrahedral stereochemistry around the cobalt(II). The ligand is bidentate andN-bonded in all cases.This work was presented in the Fifth Annual Meeting of the Portuguese Chemical Society, Porto (Portugal), March 1982.