Studies on mixed ligand complexes,part 5. Heterochelate complexes of cobalt(III) derived from the quadridentate NNNN donor ligand triethylenetetramine and bidentate OO,ON and NN donor ligands

Summary A series of new cobalt(III) complexes of general formula [Co(AA)(trien)]X_n (where AA = tropolone, acetoacetanilide, ethylacetoacetate, biguanide, 2-guanidinobenzimidazole, propylenediamine, picolylamine, 2,2-dipyridyl, 3-aminopyridine, picolinic acid and quinaldinic acid, trien = triethylenetetramine, X=Cl^–, Br^–, I^– and n=2–3) have been synthesized and characterized by elemental analysis, electronic and i.r. spectra, equivalent weight, conductance and magnetic measurements. The electronic spectra of the complexes exhibit one or two ligand field bands atca. 20000 and 29000 cm^–1 due to the¹ A _1g ¹ T _1g and¹ A _1g ¹ T _2g transitions respectively. Conductance measurements indicate the triunivalent nature of [Co(tropolone)(trien)]I₃, [Co(picolylamine)(trien)]I₃, [Co(3-aminopyridine)(trien)]I₃, [Co(2,2-dipyridyl)(trien)]Cl₃, [Co(biguanide)(trien)]I₃, [Co(propylenediamine)(trien)]I₃ and biunivalent nature of [Co(picolinate)(trien)]Cl₂, [Co(quinaldinate)(trien)]Cl₂, [Co(acetoacetanilido)(trien)]Cl₂, and [Co(ethylacetoacetato)(trien)]I₂. Equivalent weight determination by the ion-exchange resin (H⁺ form) method gives the values of molecular weights which are consistent with the theory. The complexes are diamagnetic.     

The gas‐phase ligand exchange of copper and nickel acetylacetonate,hexafluoroacetylacetonate and trifluorotrimethylacetylacetonate complexes

The gas‐phase ligand‐exchange reactions between Cu(II) and Ni(II) complexes containing the acetylacetonate (acac), hexafluoroacetylacetonate (hfac), and trifluorotrimethylacetylacetonate (tftm) ligands were investigated using a triple quadrupole mass spectrometer. The gas‐phase mixed‐ligand products of [Cu(acac)(tftm)]⁺, [Ni(acac)(tftm)]⁺, [Cu(hfac)(tftm)]⁺, and [Ni(hfac)(tftm)]⁺ were formed following the co‐sublimation of either homo‐metal or hetero‐metal precursors. The gas‐phase formation of [Cu(acac)(tftm)]⁺, [Cu(hfac)(tftm)]⁺, [Ni(acac)(tftm)]⁺, and [Ni(hfac)(tftm)]⁺ complexes is reported herein for the first time. The corresponding fragmentation patterns of these species along with those of Cu(tftm)₂ and Ni(tftm)₂ are also presented. Mass‐selected ion‐neutral reactions were investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Gas‐phase ligand exchange of select transition‐metal acetylacetonate and hexafluoroacetylacetonate complexes

Gas‐phase ligand exchange reactions between M(acac)₂ and M(hfac)₂ species, where M is Cu(II) and/or Ni(II), were observed to occur in a double‐focusing reverse‐geometry magnetic sector mass spectrometer. The gas‐phase mixed ligand product, [M(acac)(hfac)]⁺, was formed following the co‐sublimation of either homo‐metal or hetero‐metal precursors. The gas‐phase formation of [Cu(acac)(hfac)]⁺ from hetero‐metal precursors is reported herein for the first time. The [Ni(acac)(hfac)]⁺ complex is also observed for the first time to form following the co‐sublimation of not only Ni precursors, but also from separate Ni and Cu precursors. The corresponding fragmentation patterns of these species are also presented, and the mixed metal mixed ligand product [NiCu(acac)₂(hfac)]⁺ is observed. Copyright © 2008 John Wiley & Sons, Ltd.     

Photolyse von Cobalt(III)-Gemischtligandenkomplexen mit α-Aminosäuren,Ethylendiamin und 2,2′-Bipyridyl. Eliminierung der Ligandenfragmente

Photolysis of Mixed-Ligand Cobalt(II1) Complexes with α-Aminoacids, Ethylenediamine, and 2,2′-Bipyridyl. Elimination of Ligand Fragments A new organo-cobalt(III) complex, [Co(bipy)₂(η²-CH₂NH₂)]²⁺, have been obtained from UV-irradiated aqueous solutions of [Co(gly)₂bipy]⁺, [Co(bipy)₂gly]²⁺, [Co(bipy)(en)gly]²⁺, and [Co(en)₂bipy]³⁺ by ion-exchange chromatography and characterized both analytically and by IR, NMR, and UV/VIS spectra. The formation of the same product in all cases with the η²-aminomethyl ligand is explained by photoinduced elimination of the ligand fragments (CO₂ from the glycinato or CH₂NH₂⁺ from the ethylenediamine ligand) and subsequent ligand exchange reactions which are catalyzed by Co^II species. Similar photolysis products of sarcosinato or valinato complexes were found to be less stable, and hence they could be observed only at low temperatures.     

Über Reaktionen oxygenierter Kobalt(II)-Komplexe. V. Reaktivität diastereoisomerer μ-Peroxo-μ-hydroxo-dikobalt(III)-Ionen

On Reactions of oxygenated Cobalt(II) Complexes. V. Reactivity of diastereoisomeric μ-peroxo-μ-hydroxo-dicobalt(III) Ions The kinetics of dissociation of μ-peroxo-μ-hydroxo-dicobalt(III) chelates have been reinvestigated using a stopped flow technique. The binuclear cations [(trien)Co(O₂, OH) Co(trien)]³⁺, [(tren)Co(O₂, OH)Co(tren)]³⁺ and [(en)₂Co(O₂, OH)Co(en)₂]³⁺ dissociate on acidifying to Co²⁺ and the protonated ligand and up to 100% of the bound O₂ is evolved. The dissociation is H⁺-catalyzed and first order in complex. The observed rate constants at pH 2 are in the range of 10^?3 to 10^?1 s^?1 (20°). They depend not only on the nature of the ligand and on ligand configuration but also on the diastereoisomeric structure of the binuclear cation. In the case of trien there are 8 possible chemically different isomers. On oxygenation of Co(trien)²⁺ in dilute solution 3 of those isomers seem to be formed preferentially. Their rate constants are separated over a factor of 50. For [(en)₂ Co(O₂, OH)Co(en)₂]³⁺ there exist a meso form and a chiral structure. On oxygenation of Co(en)₂²⁺ in dilute solution the meso form and the racemate are formed to about equal amounts. The racemate dissociates about 5 times slower. Of the 3 possible achiral isomers of [(tren)Co(O₂, OH)Co(tren)]³⁺ one is formed stereoselectively by oxygenation in solution.     

Mono- and binuclear complexes involving [Pd(N,N-dimethylethylenediamine)(H2O)2]2+, 4,4′-bipiperidine and DNA constituents

The Pd(dmen)Cl₂, where dmen?=?N,N-dimethethylenediamine, was synthesized and characterized by elemental analysis and spectroscopy. The complex-formation equilibria in the reaction of [Pd(dmen)(H₂O)₂]²⁺ with 4,4′-bipiperidine (Bip) and DNA constituents were investigated at 25°C and 0.1?mol?L^?1 ionic strength. The results show the formation of [(H₂O)(dmen)Pd(Bip)Pd(dmen)(H₂O)]⁴⁺. Inosine, uracil, and thymine interact with the previously mentioned complex by the substitution of two-coordinated water molecules. The formation constants of all possible mono- and binuclear complexes were determined and their speciation diagrams were evaluated.     

Effect of lanthanide contraction on the mixed polyamine systems Ln/Sb/Se/(en+dien) and Ln/Sb/Se/(en+trien): Syntheses and characterizations of lanthanide complexes with a tetraelenidoantimonate ligand

Mixed polyamine systems Ln/Sb/Se/(en+dien) and Ln/Sb/Se/(en+trien) (Ln=lanthanide, en=ethylenediamine, dien=diethylenetriamine, trien=triethylenetetramine) were investigated under solvothermal conditions, and novel mixed-coordinated lanthanide(III) complexes [Ln(en)₂(dien)(η²-SbSe₄)] (Ln=Ce(1a), Nd(1b)), [Ln(en)₂(dien)(SbSe₄)] (Ln=Sm(2a), Gd(2b), Dy(2c)), [Ln(en)(trien)(μ-η¹,η²-SbSe₄)]_∞ (Ln=Ce(3a), Nd(3b)) and [Sm(en)(trien)(η²-SbSe₄)] (4a) were prepared. Two structural types of lanthanide selenidoantimonates were obtained across the lanthanide series in both en+dien and en+trien systems. The tetrahedral anion [SbSe₄]³⁻ acts as a monodentate ligand mono-SbSe₄, a bidentate chelating ligand η²-SbSe₄ or a tridentate bridging ligand μ-η¹,η²-SbSe₄ to the lanthanide(III) center depending on the Ln³⁺ ions and the mixed ethylene polyamines, indicating the effect of lanthanide contraction on the structures of the lanthanide(III) selenidoantimonates. The lanthanide selenidoantimonates exhibit semiconducting properties with E_g between 2.08 and 2.51 eV.     

Studies on the bacterial activity of cobalt(III) complexes. Part II. Cobalt(III) aminoacidato-complexes

Summary Cobalt(III) complexes of the typetrans-[Co(AA)₂(ox)] (where AA = aminoacidato, gly = glycinato, sar = sarcosinato, DL-ala = DL-alaninato, L-ala = L-alaninato; ox = oxalate); [Co(L-val)₂CO₃] and DL-[Co(en)₂sar]I₂ where L-val = L-valinato, en = ethylenediamine) have been investigated for their bacterial activity againstEscherichia coli B using well-cultured techniques on EMB agar and in minimal glucose media. The activities decrease in the order:trans-(N)(+)K[Co(sar)₂(ox)] >trans-(N)(+)K[Co(L-ala)₂(ox)] >trans-(N)(–)K[Co (gly)₂(ox)] >trans-(N)(+)K[Co(DL-ala)₂(ox)] >trans-(N)(+)K[Co(gly)₂(ox)] >trans(+)K[Co(DL-ala)₂(ox)] >trans-K[Co(L-val)₂CO₃].     

Base hydrolysis ofcis-dichlorobis(1,2-diaminoethane),cis-α-dichloro(1,8-diamino-3,6-diazaoctane) andcis-α-chlorohydroxo-(1,8-diamino-3,6-diazaoctane) ruthenium(III) complexes

The kinetics of base hydrolysis ofcis-[RuCl₂(en)₂]⁺ (en=1,2-diaminoethane),cis-α-[RuCl₂(trien)]⁺ andcis-α-[RuCl(OH)(trien)]²⁺ (trien=1,8-diamino-3,6-diazaoctane) have been studied. All the reactions are fast and obey the second-order rate law,-d[complex]/dt=k[OH⁻][complex], with complete retention of configuration. A conjugate base mechanism involving a squarepyramidal intermediate is suggested. The Arrhenius parameters and rate constants found are respectively: ΔH^≠ 14.2±0.5, 7.2±0.1, 10.9±0.1 M cal mol⁻¹; ΔS^≠ 1.3, 29, 22 cal deg⁻¹ mol; log A 13.5, 6.9, 8.6 k_OH 533 (27.2°C) 14.5 (24.4° C) 1.65 (25°C) M⁻¹s⁻¹.     

Insertion of Molecular Oxygen in Transition‐Metal Hydride Bonds,Oxygen‐Bond Activation,and Unimolecular Dissociation of Metal Hydroperoxide Intermediates. Short Communication

Thermal activation of molecular oxygen is observed for the late‐transition‐metal cationic complexes [M(H)(OH)]⁺ with M=Fe, Co, and Ni. Most of the reactions proceed via insertion in a metal? hydride bond followed by the dissociation of the resulting metal hydroperoxide intermediate(s) upon losses of O, OH, and H₂O. As indicated by labeling studies, the processes for the Ni complex are very specific such that the O‐atoms of the neutrals expelled originate almost exclusively from the substrate O₂. In comparison to the [M(H)(OH)]⁺ cations, the ion? molecule reactions of the metal hydride systems [MH]⁺ (M=Fe, Co, Ni, Pd, and Pt) with dioxygen are rather inefficient, if they occur at all. However, for the solvated complexes [M(H)(H₂O)]⁺ (M=Fe, Co, Ni), the reaction with O₂ involving O? O bond activation show higher reactivity depending on the transition metal: 60% for the Ni, 16% for the Co, and only 4% for the Fe complex relative to the [Ni(H)(OH)]⁺/O₂ couple.     

Bacterial activity of cobalt(III) complexes. Part IV: Diethylenetriaminemonoacetatocobalt(III) complexes

Summary The activities of the diethylenetriaminemonoacetatocobalt(III) complexes, [Co(en)(DTMA)]I₂, [CoX₂(DTMA)] and [CoCO₃(DTMA)]·H₂O (DTMA=diethylenetriaminemonoacetato or formally 3-amino-3, 6-diazaoctanato; en=ethylenediamine, X=Cl^–, NO ₂ ^– , NCS^–) were studied onEscherichia coli B growing in a minimal glucose medium in both lag- and log-phases. Activities decrease in the order: [Co(NCS)₂(DTMA)]> [Co(NO₂)₂(DTMA)]>[Co(en)(DTMA)]I₂>[CoCl₂(DTMA)] >[CoCO₃(DTMA)]·H₂O. The antagonistic activities of the complexes were also studied.     

Polarographic study of Eu(III)-succinate-ethylenediamine and Eu(III)-malonate-ethylenediamine mixed systems

The mixed complexes of Eu(III) with succinate (succ^2?) and malonate (mal^2?) and ethylenediamine (en) have been studied polarographically at 25°C and at constant ionic strength, μ = 0.1 (NaNO₃) and pH 6. The reduction of the complexes in each case is quasi-reversible and diffusion-controlled. In each system three mixed complexes are formed, viz. [Eu(succ)(en)]⁺, [Eu(succ)(en)2]⁺ and [Eu(succ)₂(en)]^? with stability constants log β₁₁ = 9.2, log β₁₂ = 17.5 and log β₂₁ = 11.7; and [Eu(mal)(en)]⁺, [Eu(mal)₂(en)₂]^? and [Eu(mal)₃(en)]^3? with stability constants log β₁₁ = 11.4, log β₂₂ = 19.08 and log β₃₁ = 13.5 respectively.     

Solubilities and Gibbs transfer energies of thiolato,sulfenato, sulfinato and tris(ethylenediamine)cobalt(III) complexes,as well as of perchlorate,from acetonitrile into its mixtures with water

Information on the solvation of thiolato complex cations [Co(en)₂(SCH₂COO)]⁺ [Co(en)₂(SCH₂CH(COO)NH₂)]⁺, [Co(en)₂(SCH₂CH₂NH₂)]²⁺, sulfenato complexes [Co(en)₂(SOCH₂COO)]⁺ [Co(en)₂{SOCH₂CH(COO)NH₂}]⁺, [Co(en)₂(SOCH₂CH₂NH₂)]²⁺, the sulfinato [Co(en)₂{SO₂CH₂CH(COO)NH₂}]⁺, [Co(en)₂(SO₂CH₂CH₂NH₂)]²⁺ as well as of [Co(en)₃]³⁺ has been obtained from solubility measurements in MeCN–H₂O mixtures at 298.2 K. The single-ion Gibbs energies of transfer of the Co^III complexes were derived from the solubilities of picrate and perchlorate salts for the full range of MeCN–H₂O mixtures. Single-ion Gibbs energies of transfer for the perchlorate ion are given. The effects of the solvent mixtures were interpreted in the framework of chemical bond formation between the ions and the individual solvent molecules.     

Structural models of vanadate-dependent haloperoxidases and their reactivity

Vanadium(V) complexes with hydrazone-based ONO and ONN donor ligands that partly model active-site structures of vanadate-dependent haloperoxidases have been reported. On reaction with [VO(acac)₂] (Hacac = acetylacetone) under nitrogen, these ligands generally provide oxovanadium(IV) complexes [VO(ONO)X] (X = solvent or nothing) and [VO(acac)(ONN)], respectively. Under aerobic conditions, these oxovanadium(IV) species undergo oxidation to give oxovanadium(V), dioxovanadium (V) or μ-oxobisoxovanadium(V) species depending upon the nature of the ligand. Anionic and neutral dioxovanadium(V) complexes slowly deoxygenate in methanol to give monooxo complexes [VO(OMe)(MeOH)(ONO)]. The anionic complexes [VO₂(ONO)]^- can also be convertedin situ on acidification to oxohydroxo complexes [VO(OH)(HONO)]⁺ and to peroxo complexes [VO(O₂)(ONO)]^-, and thus to the species assumed to be intermediates in the haloperoxidases activity of the enzymes. In the presence of catechol (H₂cat) and benzohydroxamic acid (H₂bha), oxovanadium (IV) complexes, [VO (acac)(ONN)] gave mixed-chelate oxovanadium(V) complexes [VO(cat)(ONN)] and [VO(bha)(ONN)] respectively. These complexes are not very stable in solution and slowly convert to the corresponding dioxo species [VO₂(ONN)] as observed by⁵¹V NMR and electronic absorption spectroscopic studies.     

Kinetic studies on chromium-glycinato complexes in acidic and alkaline media

Two solid complexes, fac–[Cr(gly)₃] and [Cr(gly)₂(OH)]₂, (where gly is glycinato ligand) were prepared and their acid-catalysed aquation products were identified. The structure of [Cr(gly)₃] was solved by X-ray diffraction, revealing a cationic 3D sublattice with perchlorate anions inside its cavities. Acid-catalysed aquation of [Cr(gly)₃] and [Cr(gly)₂(OH)]₂ leads to the same inert product, [Cr(gly)₂(H₂O)₂]⁺, in a two-stages process. At the first stage, intermediate complexes, [Cr(gly)₂(O–glyH)(H₂O)]⁺ and [Cr(gly)₂(H₂O)–OH–Cr(gly)₂(H₂O)]⁺, are formed respectively. Kinetics of the first aquation stage of [Cr(gly)₃] were studied in HClO₄ solutions. The dependencies of the pseudo first-order rate constants on [H⁺] are as follows: k _obs1H = k ₀ + k ₁ K _p1[H⁺], where k ₀ and k ₁ are rate constants for the chelate-ring opening via spontaneous and acid-catalysed reaction paths, respectively, and K _p1 is the protonation constant. The proposed mechanism assumes formation of the reactive intermediate as a result of proton addition to the coordinated carboxylate group of the didentate ligand. Some kinetic studies on the second reaction stage, the one-end bonded glycine liberation, were also done. The obtained results were analogous to those for stage I. In this case, the proposed reactive species are intermediates, protonated at the carboxylate group of the monodentate glycine. Base hydrolysis of two complexes, [Cr(gly)₂(O–gly)(OH)]⁻ and [Cr(gly)₂(OH)₂]⁻, was studied in 0.2–1.0 M NaOH. The pseudo first-order rate constants, k _obsOH, were [OH⁻] independent in the case of [Cr(gly)₂(O–gly)(OH)]⁻, whereas those for [Cr(gly)₂(OH)₂]⁻ linearly depended on [OH⁻]. The reaction mechanisms were proposed, where the OH⁻ -catalysed reaction path was rationalized in terms of formation of the reactive conjugate base, [Cr(gly)₂(OH)(O)]²⁻, as a result of OH⁻ ligand deprotonation. Activation parameters were determined and discussed.     

trans‐(Methanol)(methyl­di­phenyl­phosphine)­bis­(pentane‐2,4‐dionato)­cobalt(III) hexa­fluoro­phosphate hydrate

The title compound [Co(C₅H₇O₂)₂(C₁₃H₁₃P)(CH₄O)]PF₆·H₂O, (I), which was converted from trans‐[Co(acac)₂(PMePh₂)(H₂O)]PF₆ (acac is pentane‐2,4‐dionato) by recrystallization from aqueous methanol, has been confirmed as have a coordinated methanol ligand. The molecular structure of the complex cation, trans‐[Co(acac)₂(PMePh₂)(MeOH)]⁺, is similar to that of the above aqua complex found in the ClO₄ salt [Kashiwabara et al. (1995). Bull. Chem. Soc. Jpn, 68 , 883–888]. The Co—O bond length for the coordinated methanol is 2.059 (3) Å. There is an intermolecular hydrogen bond between the OH group of the coordinated methanol and one of the O atoms of the acac ligands in an adjacent complex cation [O5?O3′ = 2.914 (4) Å], giving a centrosymmetric dimeric dicationic complex.     

Redox Non‐Innocence and Isomer‐Specific Oxidative Functionalization of Ruthenium‐Coordinated β‐Ketoiminate

This article deals with isomeric ruthenium complexes [Ru^III(L^R)₂(acac)] (S=1/2) involving unsymmetric β‐ketoiminates (AcNac) (L^R=R‐AcNac, R=H ( 1 ), Cl ( 2 ), OMe ( 3 ); acac=acetylacetonate) [R=para‐substituents (H, Cl, OMe) of N‐bearing aryl group]. The isomeric identities of the complexes, cct (cis‐cis‐trans, blue, a ), ctc (cis‐trans‐cis, green, b ) and ccc (cis‐cis‐cis_, pink, c ) with respect to oxygen (acac), oxygen (L) and nitrogen (L) donors, respectively, were authenticated by their single‐crystal X‐ray structures and spectroscopic/electrochemical features. One‐electron reversible oxidation and reduction processes of 1 – 3 led to the electronic formulations of [Ru^III(L)(L ^? )(acac)]⁺ and [Ru^II(L)₂(acac)]^? for 1 ⁺‐ 3 ⁺ (S=1) and 1^? – 3^? (S=0), respectively. The triplet state of 1 ⁺‐ 3 ⁺ was corroborated by its forbidden weak half‐field signal near g≈4.0 at 4 K, revealing the non‐innocent feature of L. Interestingly, among the three isomeric forms ( a – c in 1 – 3 ), the ctc ( b in 2 b or 3 b ) isomer selectively underwent oxidative functionalization at the central β‐carbon (C?H→C=O) of one of the L ligands in air, leading to the formation of diamagnetic [Ru^II(L)(L ′ )(acac)] (L ′ =diketoimine) in 4 / 4′ . Mechanistic aspects of the oxygenation process of AcNac in 2 b were also explored via kinetic and theoretical studies.     

Vapochromic Ionic Liquids from Metal–Chelate Complexes Exhibiting Reversible Changes in Color,Thermal, and Magnetic Properties

Vapor‐ and gas‐responsive ionic liquids (ILs) comprised of cationic metal‐chelate complexes and bis(trifluoromethanesulfonyl)imide (Tf₂N) have been prepared, namely, [Cu(acac)(BuMe₃en)][Tf₂N] ( 1 a ), [Cu(Bu‐acac)(BuMe₃en)][Tf₂N] ( 1 b ), [Cu(C₁₂‐acac)(Me₄en)][Tf₂N] ( 1 c ), [Cu(acac)(Me₄en)][Tf₂N] ( 1 d ), and [Ni(acac)(BuMe₃en)][Tf₂N] ( 2 a ) (acac=acetylacetonate, Bu‐acac=3‐butyl‐2,4‐pentanedionate, C₁₂‐acac=3‐dodecyl‐2,4‐pentanedionate, BuMe₃en=N‐butyl‐N,N′,N′‐tetramethylethylenediamine, and Me₄en=N,N,N′,N′‐trimethylethylenediamine). These ILs exhibited reversible changes in color, thermal properties, and magnetic properties in response to organic vapors and gases. The Cu^II‐containing ILs are purple and turn blue‐purple to green when exposed to organic vapors, such as acetonitrile, methanol, and DMSO, or ammonia gas. The color change is based on the coordination of the vapor molecules to the cation, and the resultant colors depend on the coordination strength (donor number, DN) of the vapor molecules. The vapor absorption caused changes in the melting points and viscosities, leading to alteration in the phase behaviors. The IL with a long alkyl chain ( 1 d ) transitioned from a purple solid to a brown liquid at its melting point. The Ni^II‐containing IL ( 2 a ) is a dark red diamagnetic liquid, which turned into a green paramagnetic liquid by absorbing vapors with high DN. Based on the equilibrium shift from four‐ to six‐coordinated species, the liquid exhibited thermochromism and temperature‐dependent magnetic susceptibility after absorbing methanol.     

Microsolvation of the [Ni(acac)(tmen)]+ complex

Microsolvation of the [Ni(acac)(tmen)]⁺ complex by a series of aliphatic n-alcohols (Solv) has been studied in ClCH₂CH₂Cl solutions by spectrophotometry. Based on the changes in the electronic spectrum of the afore-mentioned complex, observed under the influence of any alcohol, the equilibrium constants for the formation of the [Ni(acac)(tmen)Solv]⁺ and [Ni(acac)(tmen)Solv₂]⁺ species have been computed according to the algorithm presented in this work. It was found that, in all the systems studied, the stability of five-coordinated [Ni(acac)(tmen)Solv]⁺ is higher than that of octahedral [Ni(acac)(tmen)Solv₂]⁺. The resulting values are discussed in terms of the Lewis basicity of alcohols.     

Speciation of the Ternary Complexes of Vanadium(III)–Dipicolinic Acid with the Amino Acids Glycine,Proline, <Emphasis Type="Italic">α</Emphasis>-Alanine and <Emphasis Type="Italic">β</Emphasis>-Alanine Studied in 3.0 mol⋅dm<Superscript>−3</Superscript> KCl at 25 °C

In this paper we present speciation results for the ternary vanadium(III)–dipicolinic acid (H₂dipic) systems with the amino acids glycine (Hgly), proline (Hpro), α-alanine (Hα-ala), and β-alanine (Hβ-ala), obtained by means of electromotive forces measurements emf(H) using 3.0 mol⋅dm⁻³ KCl as the ionic medium and a temperature of 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid base reactions of the ligands, which were kept fixed during the analysis. In the vanadium(III)–dipicolinic acid–glycine system, formation of the ternary [V(Hdipic)(Hgly)]²⁺, [V(dipic)(Hgly)]⁺, [V(dipic)(gly)], [V(dipic)(gly)(OH)]⁻ and [V(dipic)(gly)(OH)₂]²⁻ was observed; in the case of the vanadium(III)–dipicolinic acid–proline system the ternary complexes [V(Hdipic) (Hpro)]²⁺, [V(dipic)(Hpro)]⁺, [V(dipic)(pro)] and [V(dipic)(pro)(OH)]⁻ were observed; in the vanadium(III)–picolinic acid–α-alanine were observed [V(Hdipic)(Hα-ala)]²⁺, [V(dipic) (Hα-ala)]⁺, [V(dipic)(αala)], [V(dipic)(α-ala)(OH)]⁻ and [V(dipic)(α-ala)(OH)₂]²⁻; and in the vanadium(III)–dipicolinic acid–β-ala system the complexes [V(dipic) (Hβ-ala)]⁺, [V(dipic)(β-ala)], [V(dipic)(β-ala)(OH)]⁻ and [V(dipic)(β-ala)(OH)₂]²⁻ were observed. Their respective stability constants were determined, and we evaluated values of Δlog ₁₀ K″ in order to understand the relative stability of the ternary complexes compared to the corresponding binary ones. The species distribution diagrams are briefly discussed as a function of pH.