Speciation of the Vanadium (III) Complexes with 6-Methylpicolinic Acid,Salicylic Acid and Phthalic Acid

The complex species formed in aqueous solutions (25 °C, I=3.0 mol⋅dm⁻³ KCl ionic medium) between the V(III) cation and the ligands 6-methylpicolinic acid (MePic, HL), salicylic acid (H₂Sal, H₂L) and phthalic acid (H₂Phtha, H₂L) have been studied by potentiometric and spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the experimental emf(H) data, taking into account the hydrolytic species and hydrolysis constants of V(III), indicates that under the employed experimental conditions the complexes [VL]²⁺, [V(OH)L]⁺, [V(OH)₂L], [V(OH)₃L]⁻, [VL₂]⁺, [VL₃] and [V₂OL₄] form in the vanadium(III)–MePic system. Were observed the complexes [VL]⁺, [VL₂]⁻, [V(OH)L₂]²⁻ and [VL₃]³⁻ in the vanadium(III)–H₂Sal system, and the species [VHL]²⁺, [VL]⁺, [V(OH)L], [VHL₂], [VL₂]⁻, [V(OH)L₂]²⁻, [V(OH)₂L₂]³⁻ and [VL₃]³⁻ in the vanadium(III)–H₂Phtha system. The stability constants of these complexes were determined by potentiometric measurements, and spectrophotometric measurements were made in order to perform a qualitative characterization of the complexes formed in aqueous solution.     

Speciation of the Vanadium(III) Complexes with 1,10-Phenanthroline, 2,2′-Bipyridine,and 8-Hydroxyquinoline

The complex species formed between vanadium(III) and 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), and 8-hydroxyquinoline (8hq) were studied in aqueous solution by means of electromotive forces measurements, emf(H), at 25 °C with 3.0 mol⋅dm⁻³ KCl as the ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic vanadium(III) species formed in solution. Analysis of the vanadium(III)–phen system data shows the formation of [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes. In the vanadium(III)–bipy system the [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes were observed, and in the vanadium(III)–8hq system the complexes [V(OH)L]⁺, [V(OH)₂L], [VL₂]⁺ and [VL₃] were detected.     

Ternary Complex Formation between Vanadium(III), Dipicolinic Acid and Picolinic Acid in Aqueous Solution

Ternary complex species formed by the V³⁺ cation with the picolinic acid (Hpic, HL) and dipicolinic acid (H₂dipic, H₂L) ligands in aqueous solutions have been studied potentiometrically (25 °C, I=3.0 mol⋅dm⁻³ KCl ionic medium) and by spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the experimental emf (H) data, taking into account the hydrolytic V(III) species and the binary V³⁺–picolinic acid and V³⁺–dipicolinic acid complexes, shows that under the investigated conditions the following ternary complexes are formed: [V(dipic)(pic)], [V(dipic)(pic)(OH)]⁻ and [V(dipic)(pic)₂]⁻. The stability constants of the ternary complexes were determined by potentiometric measurements whereas the spectrophotometric measurements were done in order to obtain a qualitative characterization of the complexes formed in aqueous solution.     

Speciation of the Ternary Complexes of Vanadium(III)–Dipicolinic Acid and the Amino Acids Cysteine,Histidine, Aspartic and Glutamic Acids in 3.0 mol⋅dm<Superscript>−3</Superscript> KCl at 25 °C

In this work we present results for the speciation of the ternary complexes formed in the aqueous vanadium(III)–dipicolinic acid and the amino acids cysteine (H₂cys), histidine (Hhis), aspartic acid (H₂asp) and glutamic acid (H₂glu) systems (25 °C; 3.0 mol⋅dm⁻³ KCl as ionic medium), determined by means of potentiometric measurements. The potentiometric data were analyzed with the least-squares program LETAGROP, taking into account the hydrolysis of vanadium(III), the acid-base reactions of the ligands, and the binary complexes formed. Under the experimental conditions (vanadium(III) concentration = 2–3 mmol⋅dm⁻³ and vanadium(III): dipicolinic acid: amino acid molar ratio 1:1:1, 1:1:2 and 1:2:1), the following species [V(dipic)(H₂asp)]⁺, [V(dipic)(Hasp)], [V(dipic)(asp)]⁻, [V(dipic)(asp)(OH)]²⁻, and [V(dipic)(asp)(OH)₂]³⁻ were found in the vanadium(III)–dipicolinic acid–aspartic acid system. In the vanadium(III)–dipicolinic acid–glutamic acid system [V(Hdipic)(H₂glu)]²⁺, [V(dipic)(H₂glu)]⁺, [V(dipic)(Hglu)], [V(dipic)(Hglu)(OH)]⁻, and [V(dipic)(Hglu)(OH)₂]²⁻ were observed. In the vanadium(III)–dipicolinic acid–cysteine system the complexes [V(dipic)(H₂cys)]⁺, [V(dipic)(Hcys)], [V(dipic)(cys)]⁻, and [V(dipic)(cys)(OH)]²⁻ were present. And finally, in the vanadium(III)–dipicolinic acid–histidine system the complexes [V(Hdipic)(Hhis)]²⁺, [V(dipic) (Hhis)]⁺[\mathrm{V}(\mathrm{dipic}) (\mathrm{Hhis})]^{+}, [V(dipic)(his)], [V(dipic)(his)(OH)]⁻, and [V(dipic)(his)(OH)₂]²⁻ were observed. The stability constants of these complexes were determined. The species distribution diagrams as a function of pH are briefly discussed.     

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.     

Solution Equilibria of Ternary Systems Involving Nickel(II) Ion,Picolinic Acid,and the Amino Acids Histidine,Cysteine, Aspartic and Glutamic Acids

Solution equilibria of the ternary systems Ni(II)–picolinic acid (Hpic) and the amino acids aspartic acid (H₂asp), glutamic acid (H₂glu), cysteine (H₂cys) and histidine (Hhis), where the amino acids are denoted as H _i L, have been studied pH-metrically. The formation constants of the resulting mixed ligand complexes have been determined at 25 °C using a ionic strength 1.0 mol·dm^?3 NaCl. In the Ni(II)–Hpic–H₂asp and Ni(II)–Hpic–H₂glu systems, the complexes [Ni(pic)H₂L]⁺, Ni(pic)HL, [Ni(pic)L]^? and [Ni(pic)L(OH)]^2? were detected. In the Ni(II)–Hpic–H₂cys system the complexes [Ni(pic)H₂L]⁺ and [Ni(pic)L]^? are present. Additionally, in the Ni(II)–Hpic–Hhis system the species [Ni(Hpic)HL]²⁺, Ni(pic)L and [Ni(pic)L(OH)]^? were identified. The species distribution diagrams as functions of pH are briefly discussed.     

Study of the Ternary Complex Formation Between Vanadium(III), Dipicolinic Acid and Small Blood Serum Bioligands

Ternary complex formation reactions were studied between vanadium(III), dipicolinic acid and small molecular weight blood serum components: lactic, oxalic, citric and ortophosphoric acids. The electromotive force measurement permitted us to determine the chemical speciation of the complexes formed. In the vanadium(III)–dipicolinic acid–lactic acid system the complexes detected were: V(dipic)(lac), V(dipic)(lac)(OH)⁻ and V(dipic)(lac)(OH)₂^2-(\mathrm{OH})_{2}^{2-}. In the vanadium(III)–dipicolinic acid–oxalic acid system the observed complexes were: V(dipic)(ox)⁻, V(dipic)(ox)(Hox)²⁻ and V(dipic)(ox)₂^3-(\mathrm{ox})_{2}^{3-}. In the vanadium(III)–dipicolinic acid–citric acid system the complexes V(dipic)(Hcit)⁻, V(dipic)(cit)²⁻, V(dipic)(cit)(OH)³⁻, V(dipic)(cit)(OH)₂^4-(\mathrm{OH})_{2}^{4-} and V(dipic)(cit)(OH)₃^5-(\mathrm{OH})_{3}^{5-} were detected. Finally in the vanadium(III)–dipicolinic acid–phosphoric acid system the complexes V(dipic)(H₂PO₄) and V(dipic)(HPO₄)⁻ were observed. The UV-vis spectra allowed us to perform a qualitative characterization of the complexes formed in aqueous solution.     

Study of the Ternary Complex Formation Between Vanadium(III)-Picolinic Acid and the Amino Acids: Cysteine,Histidine, Aspartic and Glutamic Acids

The complex species formed between vanadium(III)-picolinic acid (HPic) and the amino acids: cysteine (H₂Cys), histidine (HHis), aspartic acid (H₂Asp) and glutamic acid (H₂Glu) were studied in aqueous solution by means of electromotive forces measurements emf(H) at 25 °C and 3.0 mol⋅dm⁻³ KCl as ionic medium. Data analysis using the least-squares program LETAGROP indicates the formation of ternary complexes, whose stoichiometric coefficients and stability constant were determined. In the vanadium(III)-picolinic acid-cysteine system the model obtained was: [V(Pic)(H₂Cys)]²⁺, [V(Pic)(HCys)]⁺, V(Pic)(Cys) and [V₂O(Pic)(Cys)]⁺. The vanadium(III)-picolinic acid-histidine system contained the following complexes: [V(Pic)(HHis)]²⁺, [V(Pic)(His)]⁺, V(Pic)(His)(OH) and [V(Pic)₂(HHis)]⁺. In the vanadium(III)-picolinic acid-aspartic acid system the model obtained was: V(Pic)(Asp), [V(Pic)(Asp)(OH)]⁻ and [V₂O(Pic)(Asp)]⁺ and finally, in the vanadium(III)-picolinic acid-glutamic acid system the complexes: V₂O(Pic)₂(HGlu)₂, V(Pic)(HGlu)₂ and V(Pic)₂(HGlu) were observed.     

Speciation of the nickel(II) complexes with oxalic and malonic acids studied in 1.0 mol dm−3 NaCl at 25°C

In this article, we present the results of the speciation of the binary nickel(II)-oxalic acid (H₂L) and nickel(II)-malonic acid (H₂L) systems studied by electromotive forces measurements emf (H) using 1.0?mol?dm^?3 NaCl as the ionic medium at 25°C. The experimental data were analyzed by a computational least-squares program LETAGROP/FONDO, a version of the LETAGROP program, written to analyze regular formation function and reduced formation functions, taking into account the hydrolysis of the nickel(II) cation and the acid base reactions of the ligands which were kept fixed during the analysis. In the nickel(II)-oxalic acid system the complexes [NiHL]⁺, [NiL], [Ni(OH)L]^?, and [NiL₂]^2? were observed and for the nickel(II)-malonic acid system the complexes [NiHL]⁺, [NiL], [Ni(OH)L]^?, and [Ni(OH)₂L]^2? were detected. The stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.     

Structural studies in main group chemistry : XXII. Structural and tin-119 mössbauer studies of some five-coordinate triorganotin anions

The structures of two complexes, [Ph₃PCH₂Ph]⁺[Bu₃SnCl₂⁻]⁻ and [Ph₃AsCH₂COPh]⁺[Ph₃SnCl₂]⁻, have been determined by X-ray diffraction. Both materials are monoclinic, space group P2_1/c. Unit cell data for [Ph₃PCH₂Ph]⁺−[Bu₃SnCl₂]⁻ are a 9.8521(6), b 16.9142(4), c 22.3517(7) Å, β 91.4235(9)°; and for [Ph₃AsCH₂COPh]⁺[Ph₃SnCl₂]⁻ a 34.9760(3), b 11.1290(5), c 24.2410(2) Å, β 108.56(2)°, and both consist of the component ionic species. The organotin anions each have trigonal bipyramidal geometry with equatorial organic groups and axial halogens. In the [Ph₃SnCl₂]⁻ anion the two Sn---Cl bond distances are the same (2.58(1) and 2.60(1) Å), but in [Bu₃SnCl₂]⁻, as in [Me₃SnCl₂]⁻, they are substantially different (2.573(7) and 2.689(6) Å). The Sn---C bond distances also vary: [Ph₃SnCl₂]⁻ 2.15(4), 2.16(3) and 2.25(5); [Bu₃SnCl₂]⁻ 2.21(1), 2.20(2) and 2.29(2) Å. Tin-119 Mössbauer data for these and several other similar complexes are also reported.     

Kinetic Studies of Catalyzed Chromic Acid Oxidation of Propionaldehyde by Picolinic Acid

The chromic acid oxidation of propionaldehyde in the presence of picoIinic acid proceeds much faster than that of propionaldehyde alone. It is shown that picolinic acid is an effective catalyst. The rate law governing this catalysis is rate=k[HCrO₄^?][PA]-[CH³CH²CHO][H⁺]²/(a+b[H⁺]+c[H⁺]²). A mechanism consistent with the rate law was proposed: picolinic acid reacts with chromic acid to form a cyclic intermediate complex C¹, C¹ further reacts with a molecule of hydrated aldehyde to give a termolecular complex C² and a hydrogen ion, C² then undergoes oxidative decomposition in the next step to give products.     

Mixed ligand complexes of ruthenium(III), rhodium(III) and iridium(III) with dipicolinic acid and some monobasic bidentate nitrogen,oxygen donor ligands

The trivalent ruthenium, rhodium and iridium complexes of dipicolinic acid and its mixed ligand complexes with several nitrogen, oxygen donor molecules, of types: Na[M(dipic)₂]·2H₂O and [M(dipic)(N-O)]·nH₂O (where M = Ru(III), Rh(III) or Ir(III); dipicH₂ = dipicolinic acid; NOH represents different nitrogen, oxygen donor molecules, viz., picolinic acid, nicotinic acid, isonicotinic acid, glycine, aminophenol, o- or p-aminobenzoic acid), have been synthesized and characterised on the basis of elemental analyses, electrical conductance, magnetic susceptibility measurements and spectral (electronic and infrared) data. The parent dipicolinic acid complexes are found to have a six-coordinate pseudooctahedral structure, whereas for mixed ligand complexes, a polymeric six-coordinate structure has been assigned. Various ligand field and nephelauxetic parameters have also been evaluated.     

Potentiometric and spectrophotometric titration of Cu2+ complexes with N-isopropyl-2-methyl-1,2-propanediamine

The complexation of Cu²⁺ by N-isopropyl-2-methyl-1,2-propanediamine (L) has been studied by potentiometric and spectrophotometric titration. The dominant complexes formed in this system are [CuL]²⁺, [CuL₂]²⁺, [Cu₂L₂(OH)₂]²⁺, and [CuL(OH)₂]. The data were thoroughly tested for different models with [CuL(OH)]⁺, [CuL(OH)]⁺, [Cu(OH)]⁺, and [Cu₂(OH)₂]²⁺ as additional species. The importance of steric factors is indicated by the d-d* spectra: for [CuL₂]²⁺, (λ_max = 499 nm) the absorption maximum is shifted by 50 nm to high energies relative to [Cu(en)₂]²⁺, (λ_max = 549 nm), whereas the opposite is true for the 1:1 complexes ([CuL]²⁺ : λ_max = 712 nm,s [Cu(en)]²⁺ : λ_max = 660 nm).     

Interaction Between the Low Molecular Mass Components of Blood Serum and the Vanadium(III)–2,2′-Bipyridine System

The complex species formed between vanadium(III)?C2,2??-bipyridine (Bipy) and the small blood serum bioligands lactic (HLac), oxalic (H₂Ox), citric (H₃Cit) and phosphoric (H₃PO₄) acids were studied in aqueous solution by means of electromotive forces measurements emf(H) at 25?°C and 3.0?mol?dm^?3 KCl as the ionic medium. The data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic products of vanadium(III) and the binary complexes formed. Formation of the complexes [V(Bipy)(Lac)]²⁺, [V(Bipy)(Lac)₂]⁺, [V(OH)₂(Bipy)(Lac)] and [V₂O(Bipy)₂(Lac)₂]^? were observed in the vanadium(III)?CBipy?CHLac system. Also, the species [V(Bipy)(HOx)]²⁺, [V(Bipy)(Ox)]⁺, [V(OH)(Bipy)(Ox)], [V(OH)₂(Bipy)(Ox)]^? and [V(OH)₃(Bipy)(Ox)]^2? were found in the vanadium(III)?CBipy?CH₂Ox system, the complexes [V(Bipy)(HCit)]⁺, [V(Bipy)(Cit)], [V(OH)(Bipy)(Cit)]^? and [V(OH)₂(Bipy)(Cit)]^2? were found in the vanadium(III)?CBipy?CH₃Cit system, and the species [V(Bipy)(H₂PO₄)]²⁺ and [V(Bipy)(HPO₄)]⁺ were detected in the vanadium(III)?CBipy?CH₃PO₄ system. The stability constants of these complexes were determined.     

Anion intercalation and exchange in Al(OH)3-derived compounds

Precipitation of Al³⁺ at pH = 10 in excess Li₂CO₃ leads to an anion exchanging compound, [Al₂Li(OH)₆]⁺₂CO²⁻₃. This compound exhibits, compared to [Mg₃Al(OH)₈]⁺₂CO²⁻₃, a higher degree of size selectivity in anion exchange. The structure of the [Al₂Li(OH)₆]⁺ layers is gibbsite-like, with a (110) diffraction feature at d = 4.35 Å indicating a pronounced Al³⁺ ordering. As claimed originally by Serna et al., the structure is [Al₂Li(OH)₆]⁺A^z−_1/z rather than [Al₂(OH)₆]Li⁺A^z−_1/z, with the Li⁺ coordinated in the octahedral positions left vacant by Al³⁺. This emerges from the details of a lithium-leaching process, which proposedly leads to a novel compound, [Al₂H(OH)₆]⁺A^z−_1/z.     

Mixed-Ligand Complex Formation Equilibria of Copper(II) with 6-Methylpicolinic Acid and Some Amino Acids

In this work, the ternary complex formation among copper(II), 6-methylpicolinic acid (H6Mepic) as primary ligand, and the amino acids aspartic acid (H₂Asp), glutamic acid (H₂Glu) and histidine (HHis) as secondary ligands, were studied in aqueous solution at 25 °C using 1.0 mol·dm^?3 KNO₃ as the ionic medium. Analysis of the potentiometric data using the least squares computational program LETAGROP indicates formation of the species [Cu(6Mepic)]⁺, Cu(6Mepic)(OH), [Cu(6Mepic)(OH)₂]^?, Cu(6Mepic)₂ and [Cu(6Mepic)₃]^? in the binary Cu(II)–H6Mepic system. In the ternary Cu(II)–H6Mepic–H₂Asp system the complexes [Cu(6Mepic)(H₂Asp)]⁺, Cu(6Mepic)(HAsp), [Cu(6Mepic)(Asp)]^? and [Cu(6Mepic)(Asp)(OH)]^2? were observed. In the case of the Cu(II)–H6Mepic–H₂Glu system the complexes Cu(6Mepic)(HGlu), [Cu(6Mepic)(Glu)]^?, [Cu(6Mepic)(Glu)(OH)]^2? and [Cu(6Mepic)(glu)(OH)₂]^3? were detected. Finally, in the Cu(II)–H6Mepic–HHis system the complexes [Cu(6Mepic)(HHis)]⁺, Cu(6Mepic)(His) and [Cu(6Mepic)(His)(OH)]^? were observed. The species distribution diagrams as a function of pH are briefly discussed.     

Delocalization and Valence Tautomerism in Vanadium Tris(iminosemiquinone) Complexes

To survey the noninnocence of bis(arylimino) acenaphthene (BIAN) ligands (L) in complexes with early metals, the homoleptic vanadium complex, [V(L)₃] ( 1 ), and its monocation, [V(L)₃]PF₆ ( 2 ), were synthesized. These complexes were found to have a very rich electronic behavior, whereby 1 displays strong electronic delocalization and 2 can be observed in unprecedented valence tautomeric forms. The oxidation states of the metal and ligand components in these complexes were assigned by using spectroscopic, crystallographic, and magnetic analyses. Complex 1 was identified as [V^IV(L^red)(L^.)₂] (L^red=N,N′‐bis(3,5‐dimethylphenylamido)acenaphthylene; L^.=N,N′‐bis(3,5‐dimethylphenylimino)acenaphthenesemiquinonate). Complex 2 was determined to be [V^V(L^red)(L^.)₂]⁺ at T<150 K and [V^IV(L^.)₃]⁺ at T>150 K. Cyclic voltammetry experiments reveal six quasi‐reversible processes, thus indicating the potential of this metal–ligand combination in catalysis or materials applications.     

Complexation Equilibria and Determination of Stability Constants of Binary and Ternary Nickel(II) Complexes with Amino Acids (Glycine, α-Alanine, β-Alanine and Proline) and Dipicolinic Acid as Ligands

In this paper we report the formation of binary and ternary nickel(II) complexes involving dipicolinic acid (H₂Dipic) as the primary ligand and some selected amino acids {glycine (HGly), ?-alanine (H?-Ala), ??-alanine (H??-Ala) and proline (HPro)} as secondary ligands. These complexes were studied at 25?°C by means of electromotive force measurements, emf(H), using 1.0?mol?dm^?3 NaCl as the ionic medium. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the nickel(II) cation and the acid/base reactions of the ligands whose equilibrium constants were kept fixed during the analysis. In the study of the binary nickel(II)?Camino acids systems the species [NiL]⁺, NiL₂ and [NiL₃]^? were observed, and in the case of the ternary nickel(II)?Cdipicolinic acid?Camino acids systems the complexes Ni(Dipic)HL, [Ni(Dipic)L] ^? and [Ni(Dipic)L(OH)]^2? were observed. The respective stability constants were determined, and the species distribution diagrams, as a function of pH, are briefly discussed.     

Synthesis, characterization and electron transfer properties of some picolinate complexes of ruthenium

In aqueous solution ruthenium trichloride reacted with picolinic acid (Hpic) in the presence of a base to afford [Ru(pic)₃]. In solution it shows intense ligand-to-metal charge transfer transitions near 310 and 370 nm, together with a low-intensity absorption near 2000 nm. [Ru(pic)₃] is one-electron paramagnetic and shows a rhombic ESR spectrum in 1:1 dimethylsulphoxide-methanol solution at 77 K. The distortions from octahedral symmetry have been calculated by ESR data analysis. The axial distortion is larger than the rhombic one. In acetonitrile solution it shows a reversible ruthenium(III)-ruthenium(II) reduction at −0.09 V vs. SCE and a reversible ruthenium(III)-ruthenium(IV) oxidation at 1.52 V vs. SCE. Chemical or electrochemical reduction of [Ru^III(pic)₃] gives [Ru^II(pic)₃]⁻, which in solution shows intense MLCT transitions near 360, 410 and 490 nm, and is converted back to [Ru(pic)₃] by exposure to air. Reaction of [Ru(pic)₃] with 8-quinolinol (HQ) in dimethylsulphoxide solution affords [RuQ₃]. [Ru(bpy)(pic)₂] (bpy = 2,2′-bipyridine) has been prepared by the reaction of Hpic with [Ru(bpy)(acac)₂]Cl (acac = acetylacetonate ion) in ethyleneglycol. It is diamagnetic and in solution shows intense MLCT transitions near 370, 410 and 530 nm. In acetonitrile solution it shows a reversible ruthenium(II)-ruthernium(III) oxidation at 0.44 V vs. SCE and a reversible one-electron reduction of bpy at − 1.64V vs. SCE.     

Synthesis and crystal structure of 2‐amino‐3‐hydroxypyridinium dioxido(pyridine‐2,6‐dicarboxylato‐κ3O2,N,O6)vanadate(V) and its conversion to nanostructured V2O5

2‐Amino‐3‐hydroxypyridinium dioxido(pyridine‐2,6‐dicarboxylato‐κ³O²,N,O⁶)vanadate(V), (C₅H₇N₂O)[V(C₇H₃NO₄)O₂] or [H(amino‐3‐OH‐py)][VO₂(dipic)], (I), was prepared by the reaction of VCl₃ with dipicolinic acid (dipicH₂) and 2‐amino‐3‐hydroxypyridine (amino‐3‐OH‐py) in water. The compound was characterized by elemental analysis, IR spectroscopy and X‐ray structure analysis, and consists of an anionic [VO₂(dipic)]⁻ complex and an H(amino‐3‐OH‐py)⁺ counter‐cation. The V^V ion is five‐coordinated by one O,N,O′‐tridentate dipic dianionic ligand and by two oxide ligands. Thermal decomposition of (I) in the presence of polyethylene glycol led to the formation of nanoparticles of V₂O₅. Powder X‐ray diffraction (PXRD) and scanning electron microscopy (SEM) were used to characterize the structure and morphology of the synthesized powder.