Kinetics and the Mechanism of Iron(II) Reduction of cis-α-halogeno(cetylamine) (triethylenetetramine)cobalt(III) Complex Ion in Aqueous Acid Medium

The kinetics and mechanism of iron(II) reduction of cis- α-chloro/bromo(cetylamine)(triethylenetetramine) cobalt(III) surfactant complex ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co^III using an excess of the reductant under pseudo-first-order conditions: [Fe^II = 0.25 mol dm⁻³, [H⁺ = 0.1 mol dm⁻³, [μ = 1.0 mol dm⁻³ ionic strength in a nitrogen atmosphere at 303, 308 and 313 K. The reaction was found to be second order and showed acid independence in the range [H⁺ = 0.05−0.25 mol dm⁻³. The second order rate constant increased with Co^III concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe^II], [H⁺] and [ μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of Fe²⁺(aq) with Co^III complex proceeds by an inner-sphere mechanism.     

Mechanistic Study of the Reactions of l-ascorbic Acid and Oxalic Acid with an Octahedral Manganese(IV) Complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane

The Mn^IV complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane (Mn^IVL) with phenolate-amido-amine coordination is reduced by l-ascorbic acid and oxalic acid obeying overall 1:1 stoichiometry. The reactions are biphasic and Mn^IIIL⁻ is the reactive intermediate. The product of oxidation of ascorbic acid (H₂Asc) is dehydroascorbic acid and that of oxalic acid (H₂OX) is CO₂, while Mn^II is the end product from Mn^IV. Both Mn^IVL and Mn^IIIL⁻ form outer sphere adducts with H₂Asc and H₂OX with high values of equilibrium constants of formation (Q>10² dm³ mol⁻¹, I = 0.5 mol dm⁻³, 25.8 °C, 1.5% v/v MeOH+H₂O). The adduct formation is diffusion controlled and is attributed to hydrogen bonding interactions between the reactants. The rate constants for the electron transfer in (Mn^IV/^IIIL, H₂A), (Mn^IV/^IIIL, HA⁻) (H₂A = H₂Asc, H₂OX) and for (Mn^IVL, H₂Asc)+H₂Asc, (Mn^IIIL⁻, HAsc⁻)+HAsc⁻ are reported. There was no evidence of direct coordination of the reductants to the Mn^IV/III center indicating an outer sphere (ET) mechanism.     

Oxidation of the thiosulfate ion by some iron(III) complexes with phenolate - amide-amine coordination: A comparative kinetic study

The redox reactions of thiosulfate with four iron(III) complexes having phenolate-amide-amine coordination, Fe^III(L){L = 1,2-bis(2-hydroxybenzamido)ethane, L¹; 1,3-bis(2-hydroxybenzamido)propane, L²; 1,5-bis(2-hydroxybenzamido)3-azapentane, L³; and 1,8-bis(2-hydroxybenzamido)3,6-diazaoctane, L⁴} have been investigated in 10% v/v MeOH + H₂O and I = 0.3 mol dm⁻³. At constant pH (~ 4.8) and under pseudo-first order conditions of [S₂O ₃ ²⁻ ] the reaction obeyed the rate law : − d[Fe^III(L)]/dt = k _obs [Fe^III(L)] + k _obs ^′ where k _obs ^′ denotes the observed rate constant of thiosulfate decomposition; k _obs = a[S₂O ₃ ²⁻ ] + b[S₂O ₃ ²⁻ ] _T ² is valid for all the complexes, particularly at pH < 6, while k _obs ^′ = [H⁺][S₂O ₃ ²⁻ ] _T ² is consistent with the rate law for thiosulfate decomposition proposed earlier. The rate data (k _obs) were analysed on the basis of the reactivities of various species of Fe^III(L) generated by the equilibrium protonation of the sec-NH of dien and trien spacer units resulting in the ring opening (for [Fe^III(L³/L⁴)]), and acid base equilibrium of the aqua ligand bound to the iron(III) centre ([Fe^III(L)(OH₂) _n ]). The redox activities, both for second and third order paths, show the ligand dependencies : L⁴<L³<L¹<L² conforming to the fact that the complexes tend to be less susceptible to electron transfer from S₂O ₃ ²⁻ with (i) the increase of the number of chelate rings, (ii) the decrease of overall charge, and (iii) the decrease of ring size offered by the amine moiety (from six membered to five membered one as for [Fe^III(L¹/L²)(OH₂)₂]⁺. There was no evidence for the formation of inner sphere thiosulfato complex, the possibility of the formation of the outer sphere ion-pairs, [Fe(L/HL)(OH₂)n ^+/2+, S₂O ₃ ²⁻ ] with low equilibrium constant value may not be excluded. In view of this, the outer sphere electron transfer (ET) mechanism is the most likely possibility.     

Kinetics and mechanism of the formation of (1,8)bis(2-hydroxybenzamido)3,6-diazaoctaneiron(III) and its reactions with thiocyanate, azide, acetate, sulfur(IV) and ascorbic acid in solution, and the synthesis and characterization of a novel oxo bridged diiron(III) complex. The role of phenol–amide–amine coordination

The interaction of (1,8)bis(2-hydroxybenzamido)3,6-diazaoctane (LH₂) with iron(III) in acidic medium resulted in the formation of a mononuclear complex, Fe(LH₃)⁴⁺ which further yielded, [Fe(LH₂)]³⁺, [Fe(LH)]²⁺, and [FeL]⁺ due to protolytic equilibria. The formation of [Fe(LH₃)]⁴⁺ was investigated under varying [H⁺]_T (0.01–0.10 mol dm⁻³) and [Fe³⁺]_T (1.00 × 10⁻³–1.70 × 10⁻², [L]_T = 1.0 × 10⁻⁴ mol dm⁻³) (I = 0.3 mol dm⁻³, 10% MeOH + H₂O, 25.0 °C). The reaction was reversible and displayed monophasic kinetics; the dominant path involved Fe(OH)(OH₂) ₅ ²⁺ and LH ₄ ²⁺ . The mechanism is essentially a dissociative interchange (I _d) and the dissociation of the aqua ligand from the encounter complex, [Fe(OH₂)₅OH²⁺, H₄L²⁺] is rate limiting. The ligand binds iron(III) in a bidentate ([Fe(H₃L)]⁴⁺), tetradentate ([Fe(H₂L)]³⁺), pentadentate ([Fe(HL)]²⁺) and hexadentate fashion ([FeL]⁺) under varying pH conditions. Iron(III) promoted deprotonation of the amide and phenol moieties and chelation driven deprotonation of the sec-NH ₂ ⁺ of the trien spacer unit are in tune with the above proposition. The mixed ligand complexes, [Fe^III(LH)(X)] (X = N ₃ ⁻ , NCS⁻, ACO⁻) are also reversibly formed in solution thus indicating that there is a replaceable aqua ligand in the complex conforming to its octahedral coordination, [Fe(LH)(OH₂)]²⁺, the bound ligand is protonated at the sec-NH site. Despite the multidentate nature of the ligand the Fe^III complexes are prone to reduction by sulfur(IV) and ascorbic acid. The redox reactions of different iron(III) species, Fe^III(LH_i) which involved ternary complex formation with the reductants have been investigated kinetically as a function of pH, [S^IV]_T and [ascorbic acid]_T. The substantial pK perturbation of the bound ascorbate in [Fe(LH)(HAsc/Asc)]^+/0 (ΔpK _{{[Fe(LH)(HAsc)] − HAsc − }} > 6) is considered to be compelling evidence for chelation of HAsc⁻/Asc²⁻ leading to hepta coordination of iron(III) in the ascorbate complexes. A novel binuclear complex with composition, [Fe^III ₂C₂₀N₄H₃₅O₁₁ (NO₃)] has been synthesized and characterized by i.r., u.v.–vis, e.s.r., e.s.i.-Mass, ⁵⁷Fe Mossbauer spectroscopy and magnetic moment measurements. The complex was isolated as a mixture of two forms C ₁ and C ₂ with 75.3 and 24.7%, respectively as computed from Mossbauer data. The isomer shift (δ) (quadrupole splitting, ΔE _Q) are 0.32 mm s⁻¹ (0.75 mm s⁻¹) and 0.19 mm s⁻¹ (0.68 mm s⁻¹) for C ₁ and C ₂, respectively. The variable temperature magnetic moment measurements (10–300 K) of the sample showed that C ₁ is an oxo dimer exhibiting antiferromagnetic interaction between the iron(III) atoms (S ₁ = S ₂ = 5/2, J = − 120 cm⁻¹) while the dimer C ₂ is a high spin species (S ₁ = S ₂ = 5/2) and exhibits normal paramagnetism obeying the Curie law. The cyclic voltametry response of the sample (DMF, [TEAP] = 0.1 mol dm⁻³) displayed quasi-reversible responses at − 0.577 V and − 1.451 V (versus SCE). This is in tune with the fact that the C ₂ species reverts rapidly in solution to the relatively more stable oxo-bridged dimer (C ₁) which is reduced in two sequential steps: C₁ + e⁻ → [FeL]⁺ + Fe^II; [FeL]⁺ + e⁻ → Fe^IIL, the high labilility of the Fe^II complex is attributed to the irreversibility. The X-band e.s.r. spectrum of the polycrystalline sample at room temperature displayed a weak (unresolved) band at g = 4.2 and a strong band at g = 2.0 with hyperfine splitting due to the coordinated nitrogen (I = 1). At 77 K the band at g = 4.2 is intensified while that at g = 2 is broadened to the extent of near disappearance in agreement with the presence of the exchange coupled iron(III) centres. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users. An erratum to this article is available at .     

Manganese(III)-carboxylate binding: Chemistry and structure of a hydrated pyridinedicarboxylate

The reaction of Mn(CH₃COO)₃ 2H₂O with the carboxyl-rich ligand pyridine-2,6-dicarboxylic acid (H₂L) in methanol affords a high-spin (S = 2) hydratedbis-complex. Structure determination has revealed the solid to be [Mn^III(H₂ L)(L)] [Mn^IIIL₂] 5H₂ O: space group P−1;Z = 2;a = 7.527(3)?³,b= 14.260(4)?,c = 16.080(6)?,α = 91.08(3)°,β = 103.58(3)°,γ= 105.41(3)° andV= 1611.2(10)?³. Each ligand is planar and is bonded in the tridentate O₂N fashion. The MnO₄N₂ coordination spheres show large distortions from octahedral symmetry. The lattice is stabilised by an extensive network of O…O hydrogen-bonding involving water molecules and carboxyl functions. Upon dissolution in water, protic redistribution occurs and the complex acts as the mono-basic acid Mn(HL)(L) (pK, 4.3 ±0.05). The deprotonated complex displays high metal reduction potentials: Mn^IVL₂-Mn^IIIL ₂ ⁻ , 1.05V; Mn^IIIL ₂ ⁻ Mn^IIL ₂ ²⁻ -, 0.28V vs. SCE     

Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)₂(H₂O)₂]³⁺ in CF₃SO₃H solution ([Co^III] = (2–6) × 10⁻³ m, [ptz] = 2.5 × 10⁻⁴ m, [H⁺] = 0.02 − 0.05 m, I = 0.1 m (H⁺, K⁺, CF₃SO ₃ ⁻ ), T = 288–308 K) and [Co(edta)]⁻ in aqueous HCl ([Co^III] = (1 − 4) × 10⁻³ m, [ptz] = 1 × 10⁻⁴ m, [H⁺] = 0.1 − 0.5 m, I = 1.0 m (H⁺, Na⁺, Cl⁻), T = 313 − 333 K) were studied under the condition of excess Co^III using u.v.–vis. spectroscopy. The reactions produce a Co^II species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k _obs) on [Co^III] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)₂(H₂O)₂]³⁺ ion was found to be independent of [H⁺]. In the case of the [Co(edta)]⁻ ion, the k _obs dependence on [H⁺] was linear and the increasing [H⁺] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows: ΔH ^≠ = 105 ± 4 kJ mol⁻¹, ΔS ^≠ = 93 ± 11 J K⁻¹mol⁻¹ for [Co(en)₂(H₂O)₂]³⁺; ΔH ^≠ = 67 ± 9 kJ mol⁻¹, ΔS ^≠ = − 54 ± 28 J K⁻¹mol⁻¹ for [Co(edta)]⁻.     

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

The reactions between Fe(Phen)₃²⁺[phen = tris-(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm⁻³ (NaCl/HCl). Plots of k₂ versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (Z_AZ_B) for the reactions of Fe(Phen)₃²⁺ with the chloro-, bromo- and iodo- complexes respectively. Z_AZ_B of ≈ −2 suggests that the charge on these Co^III complexes cannot be −3 but is −1. This suggests the possibility of protonation of these Co^III complexes. Protonation was investigated over the range [H⁺] = 0.0001 −0.06 mol dm⁻³ and the protonation constants K_a obtained are 1.22 × 10³, 7.31 × 10³ and 9.90 × 10² dm⁶ mol⁻³ for X = Cl, Br and I, respectively.     

Kinetics of oxidation of glutathione by an octahedral cobalt(III) complex with phenolate–amide–amine coordination

The reduction of the octahedral cobalt(III) complex Co^III(HL)·9H₂O, H₄L = 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane by glutathione (GSH) has been studied by conventional spectrophotometry at 25.0 ≤ t/°C ≤ 45.0, 0.02 ≤ [H⁺]/mol dm^?3 ≤ 0.20 and I = 0.3 mol dm^?3 (NaClO₄). The reaction is biphasic. The fast initial phase is attributed to the H⁺-induced formation of the mixed ligand complex, [Co^III(H₂L)GSH]⁺, for which the rate-limiting step is the chelate ring opening via Co^III–NH (amide–N) bond cleavage of the protonated species, [Co^III(H₂L)]⁺. Outer-sphere association equilibria between GSH/GSH₂ ⁺ and [Co^III(H₂L)]⁺ substantially retard the ring opening process and consequently the mixed ligand complex formation. This is then followed by a slow phase involving reduction of [Co^III(H₂L)GSH]⁺ by both GSH and GSH₂ ⁺. The final products are the corresponding Co(II) complex and the oxidized form of GSH, GS–SG. The kinetic data and activation parameters for the redox process are interpreted in terms of an outer-sphere electron transfer mechanism.     

Novel oxalate-bridged trinuclear FeIII-MII-FeIII (M = Cu and VO) complexes: synthesis and magnetism

Two new heterotrinuclear Fe^III-M^II-Fe^III oxalate-bridged complexes have been prepared, and characterized, namely M^II[(ox)Fe^III(Salen)]₂, [Salen = N,N′-ethylenebis(salicylideneiminate), ox = oxalate, M = Cu (1) and VO (2)]. Based on elemental analysis, conductivity measurements and i.r. spectra, the complexes are proposed to have an oxalate-bridged structure. The magnetic susceptibilities of the complexes were measured over the 4.2–300 K range, giving the exchange integrals J _AB = −4.23 cm⁻¹, J _AA = −2.47 cm⁻¹ for (1) and J _AB = −5.42 cm⁻¹, J _AA = −1.55 cm⁻¹ for (2). These results revealed the operation of an antiferromagnetic spin-exchange interaction between the metal ions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Inner-sphere oxidation of ternary nitrilotriacetatocobalt(II) complexes involving oxalate and phthalate by periodate

The oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ and [Co^II(nta)(ph)(H₂O)₂]³⁻ (nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ by periodate, obeys the following equation: d[Co^III]/dt = [Co^II(nta)(ox)(H₂O)₂³⁻][H₅IO₆] {k ₄ K ₅ + (k ₅ K ₆ K ₂/[H⁺]} while the reaction of [Co^II(nta)(ph)(H₂O)₂]³⁻ with periodate in aqueous acidic medium obeys the following rate law: d[Co^III]/dt = k ₆ K ₈[Co^II]_T [I^VII]_T/{1 + [H⁺]/K ₇ + K ₈[I^VII] _T }. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes by periodate is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions.     

Cobalt(II) complexes with aminopolycarboxylate 1,3-pdta-type ligands: synthesis and characterization of trans(O6)-[Mg(H2O)6][CoII(1,3-pddadp)]·H2O

Starting from Ba₂(1,3-pddadp)·8H₂O (1,3-pddadp=1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate ion) and CoSO₄, a new hexadentate [Co^II(1,3-pddadp)]²⁻ complex has been prepared. The trans(O₆) geometry of this complex was confirmed by comparison of its i.r. and u.v.–vis. spectra with those of [Co^II(1,3-pdta)]²⁻ (1,3-pdta is the 1,3-propanediaminetetraacetate ion) and trans(O₆)-[Co^III(1,3-pddadp)]⁻ complexes of known X-ray crystal structure. Magnetic and electrolytic conductivity properties of these complexes have also been discussed.     

Synthesis, crystal structures and properties of the novel mononuclear copper(II) and tetranuclear cobalt(II) complexes with 3,6-bis-(3,5-dimethylpyrazolyl)-pyridazine

A novel monomer copper(II) complex [Cu(L)₂(SCN)] · ClO₄ (1) and a tetranuclear cobalt(II) complex [Co₄(L)₄(N₃)₄](OH)₄ · 2H₂O (2)(L = 3,6-bis-(3,5-dimethylpyrazolyl)-pyridazine) have been synthesized and structurally characterized. Single crystal X-ray analyses show that the Cu(II) atom is in a distorted trigonal bipyramidal coordinated environment consisting of four N atoms of L and one N atom of SCN⁻ in complex (1), and the monomer is extended to a 1D chain by the weak intermolecular π...π stacking interactions. In the complex (2), four Co(II) atoms are linked by four bridging azido groups in μ-1,1-N₃ (end-on) coordination mode to form a tetranuclear configuration. The fungicidal activity of the title compounds have been studied, and the results show that there are certain activities against several bacteria for the complexes and the ligand. Furthermore, two complexes exhibit blue emission fluoresce in the solid state at room temperature.     

Synthesis,DNA-binding and photocleavage studies of cobalt(III) complexes [Co(bpy)<Subscript>2</Subscript>(dpta)]<Superscript>3+</Superscript> and [Co(bpy)<Subscript>2</Subscript>(amtp)]<Superscript>3+</Superscript>

Two novel cobalt(III) mixed-polypyridyl complexes [Co(bpy)₂(dpta)]³⁺ and [Co(bpy)₂(amtp)]³⁺ (bpy = 2,2′-bipyridine, dpta = dipyrido-[3,2-a;2′,3′-c]-thien-[3,4-c]azine, amtp = 3-amino-1,2,4-triazino[5,6-f]-1,10-phenanthroline) have been synthesized and characterized. The interaction of Co^III complexes with calf thymus DNA was investigated by spectroscopic and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, Co^III complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The mechanism studies reveal that hydroxyl radical (OH^•) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(bpy)₂(dpta)]³⁺ and superoxide anion radical (O ₂ ^•− ) acts as the key role in the cleavage reaction of plasmid DNA by [Co(bpy)₂(amtp)]³⁺.     

Synthesis and spectral characterization of macrocyclic Schiff base by reaction of 2,6-diaminopyridine and 1,4- bis (2-carboxyaldehydephenoxy)butane and its CuII, NiII, PbII, CoIII and LaIII complexes

A new macrocyclic ligand, 1,3,5-triaza-2,4:7,8:15,16-tribenzo-9,15-dioxacycloheptadeca-1,5-diene (L) was synthesized by reaction of 2,6-diaminopyridine with 1,4-bis(2-carboxyaldehydephenoxy)butane. Then, its Cu^II, Ni^II, Pb^II, Co^III and La^III complexes were synthesized by the template effect by reaction of 2,6-diaminopyridine and 1,4-bis (2-carboxyaldehydephenoxy)butane and Cu(NO₃)₂ · 3H₂O, Ni(NO₃)₂ · 6H₂O, Pb(NO₃)₂, Co(NO₃)₂ · 6H₂O, La (NO₃)₃ · 6H₂O, respectively. The ligand and its metal complexes were characterized by elemental analysis, IR, ¹H- and ¹³C-n.m.r., UV-vis spectra, magnetic susceptibility, thermal gravimetric analysis, conductivity measurements and mass spectra. All complexes are diamagnetic and the Cu^II complex is binuclear. The Co^II complex was oxidised to Co^III.     

Mononuclear nine-coordinate Na[SmIII(edta)(H2O)3] · 5H2O and one dimensional unlimited ladderlike eight-coordinate {[SmIII(Hpdta)(H2O)] · 2H2}On Complexes: Synthesis and Structural Determination

The Na[Sm^III(edta)(H₂O)₃] · 5H₂O (H₄edta = ethylenediamine-N,N,N′,N′-tetraacetic acid) and {[Sm^III(Hpdta)(H₂O)] · 2H₂O} _n (H₄pdta = propylenediamine-N,N,N′,N′-tetraacetic acid) complexes were prepared with heat-refluxing and acidity-adjusting methods, respectively. And their composition and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques. The Na[Sm^III(edta)(H₂O)₃] · 5H₂O complex shapes a mononuclear structure, and crystallizes in the orthorhombic crystal system with space group Fdd2. The central Sm^III ion is nine-coordinated by one hexadentate edta ligand and three water molecules. The crystal data are as follows: a = 19.139(10) ?, b = 35.00(2) ?, c = 11.928(10) ?, V = 7989(9) ?³, Z = 16, D _c = 2.014 g/cm³, μ = 3.046 mm⁻¹, F(000) = 4848, R = 0.0439, and wR = 0.0941 for 3434 observed reflections with I ≥ 2σ(I). The SmN₂O₇ part in [Sm^III(edta)(H₂O)₃]⁻ complex anion forms a pseudo-monocapped square antiprismatic polyhedron. The {[Sm_III(Hpdta)(H₂O)] · 2H₂O} _n complex is prepared with protonated pdta ligand firstly, which forms one dimensional unlimited ladderlike eight-coordinated structure, and crystallizes in the monoclinic crystal system with space group P2₁/n. The central Sm^III ion, in one construction unit, is coordinated by two nitrogen atoms from one hexadentate pdta ligand and six oxygens from the same pdta ligand, one water molecule and one carboxylic group of neighbour pdta ligand, respectively. The crystal data are as follows: a = 12.720(3) ?, b = 9.3800(19) ?, c = 14.420(3) ?, β = 96.11(3)°, V = 1710.7(6) ?³, Z = 2, D _c = 1.971 g/cm³, μ = 3.492 mm⁻¹, F(000) = 1004, R = 0.0225 and wR = 0.0607 for 3182 observed reflections with I ≥ 2σ(I). Otherwise, each part of SmN₂O₆ in {[Sm^III(Hpdta)(H₂O)] · 2H₂O} complex segment adopts a pseudo-square antiprismatic polyhedron.     

Supramolecular cobalt(II) complexes: syntheses,crystal structures and solvent effects

Two Co^II complexes, namely {[CoL(MeOH)(μ-OAc)]₂Co}·2MeCN·2MeOH (1) and {[CoL(EtOH)(μ-OAc)]₂Co}·3EtOH (2) (H₂L=3,3′-dimethoxy-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol), have been synthesized and characterized by X-ray crystallography. Both complexes contain octahedral coordination geometries, comprising three Co^II atoms, two deprotonated bisoxime L²⁻ units in which four μ-phenoxo oxygen atoms form two [CoL(X)] (X = MeOH or EtOH) units, two acetate ligands coordinated to three Co^II centers through Co–O–C–O–Co bridges, and coordinated and non-coordinated solvent. Both complexes exhibit 2D supramolecular networks through different intermolecular hydrogen-bonding interactions.     

Base hydrolysis ofcis-(methyl/ethylamine)bis(ethylenediamine) (salicylato)cobalt(III) complexes

The kinetics of the base hydrolysis ofcis-[Co(en)₂(RNH₂)-(SalH)]²⁺ (R=Me or Et; SalH=HOC₆H₄CO ₂ ⁻ ) were investigated in aqueous ClO ₄ ⁻ in the 0.004–0.450 mol dm⁻³ [OH⁻] range, I=0.50 mol dm⁻³ at 30–40°C. The phenoxide species is hydrolysed via [OH⁻]-independent and [OH⁻]-dependent paths, the latter being first order in [OH⁻]. The high rate of alkali-independent hydrolysis of the phenoxide species is associated with high ΔH^≠ and ΔS^≠ values, in keeping with the SNICB mechanism involving an amido conjugate base generated by the phenoxide-assisted NH-deprotonation of the coordinated amine. The [OH⁻]-dependent path also involves the conventional SN₁ CB mechanism. The rate constant, k₁, for the SNICB path exhibits a steric acceleration with the increasing size of the non-labile alkylamine, whereas the rate constant, k₂, for the SN₁CB path shows a reverse trend. TMC 2578     

Kinetics and mechanism of complexation of iron(III) bycis-(salicylato)(methyl/ethylamine)bis(ethylenediamine)cobalt(III) ions

The formation and dissociation of the binuclear complexes of Fe^III withcis-[Co(en)₂(RNH₂)SalH]²⁺ [R=Me, Et and SalH=C₆H₄(OH)CO ₂ ⁻ ] were studied by a stopped-flow technique at 20–35°C, and I=1.0 mol dm⁻³ (ClO ₄ ⁻ ). The formation of the binuclear species, N₅CoSalFe⁴⁺, involves reactions of the phenol form of the Co^III substrates with Fe(OH₂) ₆ ³⁺ and Fe(OH₂)₅OH²⁺. The mechanism of reaction of Fe(OH₂)₅OH²⁺ is essentially Id, while that of Fe(OH₂) ₆ ³⁺ appears to be Ia. The formation rate constant, k₁, for Fe(OH₂) ₆ ³⁺ /N₅CoSalH²⁺ reaction decreases as the amine chain length increases, whereas the same (k₂) for the Fe(OH₂)₅OH²⁺/N₅CoSalH²⁺ reaction does not show any such trend. The binuclear species, N₅CoSalFe⁴⁺, dissociates to yield a Co^III substrate and Fe^III speciesvia a predominantly spontaneous dissociation path and a minor acid catalysed path which are relatively insensitive to the variation in size of the non-labile amine chain length.     

Synthesis and structure of cobalt α-dioximate complexes with isonicotinamide

New cobalt trans-dioximate complexes with isoniconinamide have been synthesized: [Co^II(DmgH)₂(Inia)₂] (I), [Co^III(DmgH)₂(Inia)₂][PF₆] · 1.5H₂O (II), [Co^III(NioxH)₂ (Inia)₂][PF₆] · H₂O · CH₃OH (III), and [CoIIICl(DmgH)₂(Inia)] · H₂O (IV), where DmgH⁻ and NioxH⁻ are the dimeth-ylglyoxime and 1,2-cyclohexanedionedioxime monoanions, respectively; Inia is the isonicotinamide molecule. The structures of compounds I–IV have been determined by X-ray crystallography. In I–IV, Co(II) or Co(III) has an octahedral environment with the pseudomacrocyclic (DioxH⁻)₂ moiety (DioxH⁻ is the dioximate monoanion) in the equatorial plane. The latter is stabilized by O-H…O hydrogen bonds. The isonicotinamide molecules in all four complexes are monodentately bound to the metal ion through the heterocyclic nitrogen atom.     

Equilibrium study on the reactions of boric acid with some cis -diaqua CrIII-complexes

Substitution inertcis-diaqua Cr^III complexes: cis-[(L^x−)Cr^III(H₂O)₂]^(3−x)+ derived from N-donor ligands (L^x−) viz., bipyridine and 1,10-phenanthroline (x = 0) and N,O-donor ligands viz., nitrilotriacetate and anthranilate N,N-diacetate (x = 3) titrate as diprotic acids in aqueous solution and enhance the acidity of otherwise weakly acidic boric acid (H₃BO₃) producing mononuclear and binuclear mixed ligand Cr^III-borate complexes: [(L)Cr(H₂BO₄)]^x− and [(L)Cr(BO₄)Cr(L)]^(1−2x)+ respectively through coordination of the H₂O and/or OH⁻ ligands, cis-coordinated in the Cr^III-complexes on the electron deficient B^III-atom in H₃BO₃ with release of protons. Deprotonation of the parent Cr^III-complexes and their reactions with H₃BO₃ have been investigated by potentiometric method in aqueous solution,I = 0.1 mol dm⁻³ (NaNO₃) at 25 ±0.1°C. The equilibrium constants have been evaluated by computerized methods and the tentative stoichiometry of the reactions have been worked out on the basis of the speciation curves