Syntheses and X-ray crystal structures of [Co(η-CO3)(NH3)4](NO3)·0.5H2O and [(NH3)3Co(μ-OH)2(μ-CO3)Co(NH3)3][NO3]2·H2O

[Co(η²-CO₃)(NH₃)₄](NO₃)·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O were prepared by prolonged aerial oxidation of a solution of Co(NO₃)₂·6H₂O and ammonium carbonate in aqueous ammonia. The formation of these side products highlights the richness of the chemistry of these systems and the possibility of by products if methods are not strictly adhered to. The X-ray crystal structures of [Co(η²-CO₃)(NH₃)₄][NO₃]·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O reveal a monomeric octahedral cobalt center with η²-bound CO₃²⁻ in the former, while the latter consists of a dimeric array where the two cobalt centers are bridged by two OH⁻ and one μ₂-CO₃²⁻ groups with three terminal NH₃ ligands for each Co center. In both complexes extensive hydrogen bonding interactions are evident.     

Tetra(μ3-hydroxo)hexa(μ2-carboxylato-O,O′)-bridged tetranuclear terbium(III) cubane complex

A novel tetranuclear terbium(III) complex [Tb₄(OH)₄(pybet)₆(H₂O)₈][Tb₄(OH)₄(pybet)₆(H₂O)₇ (NO₃)](ClO₄)₁₄·6H₂O has been synthesized and shown by X-ray crystallography to have a cubane-like Tb₄(μ₃-OH)₄(μ₂-carboxylato-O,O′)₆ core. The ligand pybet is pyridinoacetate, C₅H₅⁺N-CH₂CO₂⁻. Magnetic susceptibility data were measured for this Tb₄ complex in the range of 2.0–320 K and in fields of 1.0 G to 50.0 kG. It is concluded that either there is very weak antiferromagnetic exchange interaction (J = −0.015 cm⁻¹) or there is a small crystal-field splitting of the ⁷F₆ Tb^III ground state.     

The electrolyte NRTL model and speciation approach as applied to multicomponent aqueous solutions of H2SO4, Fe2(SO4)3, MgSO4 and Al2(SO4)3 at 230–270 °C

This work presents chemical modeling of solubilities of metal sulfates in aqueous solutions of sulfuric acid at high temperatures. Calculations were compared with experimental solubility measurements of hematite (Fe₂O₃) in aqueous ternary and quaternary systems of H₂SO₄, MgSO₄ and Al₂(SO₄)₃ at high temperatures. A hybrid model of ion-association and electrolyte non-random two liquid (ENRTL) theory was employed to fit solubility data in three ternary systems H₂SO₄–MgSO₄–H₂O, H₂SO₄–Al₂(SO₄)₃–H₂O at 235–270 °C and H₂SO₄–Fe₂(SO₄)₃–H₂O at 150–270 °C. Employing the Aspen Plus™ property program, the electrolyte NRTL local composition model was used for calculating activity coefficients of the ions Al³⁺, Mg²⁺ Fe³⁺ and SO₄²⁻, HSO₄⁻, OH⁻, H₃O⁺, respectively, as well as molecular species. The solid phases were hydronium alunite (H₃O)Al₃(SO₄)₂(OH)₆, hematite Fe₂O₃ and magnesium sulfate monohydrate (MgSO₄)·H₂O which were employed as constraint precipitation solids in calculating the metal sulfate solubilities. A correlation for the equilibrium constants of the association reactions of complex species versus temperature was implemented. Based on the maximum-likelihood principle, the binary interaction energy parameters for the ionic species as well as the coefficients for equilibrium constants of the reactions were obtained simultaneously using the solubility data of the ternary systems. Following that, the solubilities of metal sulfates in the quaternary systems H₂SO₄–Fe₂(SO₄)₃–MgSO₄–H₂O, H₂SO₄–Fe₂(SO₄)₃–Al₂(SO₄)₃–H₂O at 250 °C and H₂SO₄–Al₂(SO₄)₃–MgSO₄–H₂O at 230–270 °C were predicted. The calculated results were in excellent agreement with the experimental data.     

Optimised hydrothermal synthesis of multi-dimensional hybrid coordination polymers containing flexible organic ligands

In this paper, we summarise our recent research interest in the hydrothermal synthesis and structural characterisation of multi-dimensional coordination polymers. The use of N-(phosphonomethyl)iminodiacetic acid (also referred to as H₄pmida) in the literature as a versatile chelating organic ligand is briefly reviewed. This molecule plays an important role in the formation of centrosymmetric dimeric [V₂O₂(pmida)₂]⁴⁻ anionic units, which were first used by us as building blocks to construct novel coordination polymers. Starting with [V₂O₂(pmida)₂]⁴⁻ in solution, we have isolated [M₂V₂O₂(pmida)₂(H₂O)₁₀] species (where M²⁺ = Mn²⁺, Co²⁺ or Cd²⁺) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4′-bpy)(H₂O)₂]·(4,4′-bpy)_0.5·(H₂O), [CoVO(pmida)(4,4′-bpy)(H₂O)₂]·(4,4′-bpy)_0.5, [Co(H₂O)₆][CoV₂O₂(pmida)₂(pyr)(H₂O)₂]·2(H₂O) and [Cd₂V₂O₂(pmida)₂(pyr)₂(H₂O)₄]·4(H₂O) by the inclusion of bridging organic ligands in the reactive mixtures, such as pyrazine (pyr) and 4,4′-bipyridine (4,4′-bpy). These materials can contain channel systems, and exhibit magnetic behaviour, not only due to the V⁴⁺ centres but also to the transition metal centres which establish the links between neighbouring dimeric [V₂O₂(pmida)₂]⁴⁻ anionic units. A closely related anionic moiety, [Ge₂(pmida)₂(OH)₂]²⁻, was engineered to allow the study of such crystalline hybrid materials using one- and two-dimensional high-resolution solid-state NMR.     

Synthesis, characterization and reactivity of some novel dinuclear mixed-ligand peroxouranium(VI) complexes

Novel anionic dinuclear mixed-ligand peroxo complexes of the type [(UO₂)₂(O₂)₃L(H₂O)₂]³⁻ (L = Histidinate, aspartate, salicylate, Imidazolate and glutamate) have been synthesized from the interaction of uranyl ion (UO₂²⁺) with peroxide (O₂²⁻) in the presence of the respective coligand (L) at pH 9–10. The sparingly soluble complexes were characterized by elemental analyses, FT-IR, laser Raman (LR) and UV-vis spectroscopy and solution electrical conductance measurements. Based on these studies, a double bridged dinuclear structure involving one peroxo and the mixed ligand L (via-COO⁻) has been tentatively proposed. Infra-red coupled with LR spectra evidenced structurally different metal bound peroxides (ν² and σ:σ). An aqueous solution of the salicylate and aspartate complexes have been shown to convert triphenylphosphine (PPh₃), cyclohexene, styrene and SO₂ to the corresponding OPPh₃, 1,2 cyclohexanediol, phenylethyleneglycol and SO₄²⁻, respectively.     

On the origin of the splittings of the ν3(SO4) modes in the specular reflectance IR spectra of gypsum

The IR polarized spectra of gypsum CaSO₄·2H₂O were recorded at incidence angles of approximately 10 and 16 degrees. Band singlet or doublet was observed for the higher frequency ν₃(SO₄²⁻) mode of B_u symmetry type, depending on polarization (n or p). A doublet was observed for the lower frequency ν₃(SO₄²⁻) mode of B_u symmetry type too, irrespectively of the type of polarization. In order to give an explanation for the doublets origin, a model permittivity function was constructed. Quite good agreement exists between the reflectance based on the model permittivity function and the experimentally measured one for the high-frequency doublet. The origin of the lower frequency doublet could not be explained in this way, but may be speculated to result from an Evans type interaction between a combination of a water libration and ν₂(SO₄²⁻), with the lower frequency ν₃(SO₄²⁻) mode.     

Synthesis, characterization and structure of complexes of o-aminophenol-N,N,O-triacetic acid with cobalt(II), nickel(II), manganese(II) and zinc(II)

The potassium salt of o-aminophenol-N,N,O-triacetic acid (APTA) and KMnL·H₂O, KCoL·3H₂O, KNiL·3H₂O, KZnL·3ZH₂O, Co(CoL)₂·7H₂O and Ni(NiL)₂·8H₂O(L³⁻:anion of APTA) have been synthesized and characterized by elementary analysis, thermogravimetric analysis, molar conductance, IR spectra, magnetic measurements and electronic spectra. The coordination environments of these metal ions have been discussed on the basis of these studies. The single crystal structure of cobalt(II)-APTA has been determined as CoL·0.5Co(H₂O)₆·4H₂O, which contains two types of cobalt(II). One type of cobalt(II) is coordinated with six water molecules to form Co(H₂O)₆²⁺, the other is chelated by APTA to form a distorted octahedron and linked into an infinite chain anion [COC₆H₄(OCH₂COO)N(CH₂COO)₂⁻]_n, in which each cobalt(II) atom is linked with neighbouring cobalt(II) atoms through two carboxylate oxygen atoms of the phenoxyacetate group. Water molecules occupy interstices in the structure.     

Kinetics of formation and dissociation of the ternary complex ion (pentane-2,4-dionato)(nitrilotriacetato)chromate(III) in aqueous media

Synthesis of solid [Cr(nta)(H₂O)₂] 1, kinetics and equilibrium of ots reaction with pentane-2,4-dione (Hpd) to form [Cr(nta)(pd)]⁻ 2 (H₃nta is nitrilotriacetic acid), aquation of 2 into 1, and some related reactions have been described. Parallel proton-independent and inverse proton-dependent paths lead from 1 to 2. The [H⁺]⁻¹ path arises from metal assisted deprotonation of HE, the enol form of Hpd. Aquation of 2 into 1 involves [Cr(Hnta)(pd)(H₂O]⁺ 2H (Hnta is tridentate nta) in addition to 2. The nta comples 1 is considerably more labile and a weaker acid than [Cr(H₂O)₆]³⁺.     

Synthesis and magnetism of the first tetranuclear copper(II)–iron(III) complexes of macrocyclic oxamides

Four novel tetranuclear macrocyclic complexes of the formula [(CuLⁱ)₃Fe](ClO₄)₃·3H₂O (i=1–4, Lⁱ are the dianions of the [14]N₄ and [15]N₄ macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene, 2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene] have been prepared and characterized. These complexes are the first examples of oxamido-bridged Cu(II)–Fe(III) heterometallic species. Cryomagnetic studies on [(CuL¹)₃Fe](ClO₄)₃·3H₂O (1) and [(CuL³)₃Fe](ClO₄)₃·3H₂O (3) (77–300 K) revealed that the Cu(II) and Fe(III) ions interact antiferromagnetically through the oxamido bridge, with the exchange integral J=−30.8 cm⁻¹ for 1 and J=−28.7 cm⁻¹ for 3 based on . The interaction parameters have been compared with that of the related [Cu₃Mn] compound.     

Hydrothermal synthesis, crystal structure and characterization of [Zn(H2O)4]2 [H2As6V15O42(H2O)]·2H2O

The compound [Zn(H₂O)₄]₂[H₂As₆V₁₅O₄₂(H₂O)]·2H₂O (1) has been synthesized and characterized by elemental analysis, IR, ESR, magnetic measurement, third-order nonlinear property study and single crystal X-ray diffraction analysis. The compound 1 crystallizes in trigonal space group R3, a=b=12.0601(17) Å, c=33.970(7) Å, γ=120°, V=4278.8(12) Å³, Z=3 and R1(wR2)=0.0512 (0.1171). The crystal structure is constructed from [H₂As₆V₁₅O₄₂(H₂O)]⁴⁻ anions and [Zn(H₂O)₄]²⁺ cations linked through hydrogen bonds into a network. The [H₂As₆V₁₅O₄₂(H₂O)]⁶⁻ cluster consists of 15 VO₅ square pyramids linked by three As₂O₅ handle-like units.     

Large heteropolymetalate complexes formed from lanthanide (Y, Ce, Pr, Nd, Sm, Eu, Gd), nickel cations and cryptate [As4W40O140]: synthesis and structure characterization

A new family of heteropolytungstate complexes (NH₄)₂₁[Ln(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀]·xH₂O(Ln=Y, Ce, Pr, Nd, Sm, Eu, Gd) were prepared by the reaction of Na₂₇[NaAs₄W₄₀O₁₄₀]·60H₂O with NiCl₂·6H₂O and Ln(NO₃)₃·xH₂O at pH≈4.5. The crystal structures of (NH₄)₂₁[Gd(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀]·51H₂O was determined by X-ray diffraction analysis and element analysis. The compound crystallizes in the monoclinic space group P2₁/n with a=19.754(3), b=24.298(4), c=39.350(6) Å, β=100.612(3)°, V=18564(5) ų, Z=2, R1(wR₂)=0.0544(0.0691). The central site S1 and two opposite sites S2 of the big cyclic ligand [As₄W₄₀O₁₄₀]²⁸⁻ are occupied by one Ln³⁺and two Ni²⁺, respectively, each site supply four O_d coordinating to metal ion, another one water molecule and other five water molecules coordinate, respectively, to Ni²⁺and Ln³⁺. Polyanion [Ln(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀]²¹⁻ has C_2v symmetry. IR and UV–vis spectra of [NaAs₄W₄₀O₁₄₀]²⁷⁻ of the title compounds are discussed.     

Photophysics of ruthenium(II) complexes with 2-(2′-pyridyl) pyrimidine and 2,2′-bipyridine ligands in fluid solution

The photophysics of three complexes of the form Ru(bpy)₃₋(pypm)²⁺ (where bpy2,2′-bipyridine, pypm 2-(2′-pyridyl)pyrimidine and P=1, 2 or 3) was examined in H₂O, propylene carbonate, CH₃CN and 4:1 (v/v) C₂H₅OH---CH₃OH; comparison was made with the well-known photophysical behavior of Ru(bpy)₃²⁺. The lifetimes of the luminescent metal-to-ligand charge transfer (MLCT) excited states were determined as a function of temperature (between −103 and 90 °C, depending on the solvent), from which were extracted the rate constants for radiative and non-radiative decay and ΔE, the energy gap between the MLCT and metal-centered (MC) excited states. The results indicate that ^*Ru(bpy)₂(pypm)²⁺ decays via a higher lying MLCT state, whereas ^*Ru(pypm)₃²⁺ and ^*Ru(pypm)₂(bpy)²⁺ decay predominantly via the MC state.     

Hydrogenmaleato bridged supramolecular double chains via π–π stacking interactions: syntheses, crystal structures and magnetic properties of ∞[Cu(phen)X(HL)2/2] with X=Cl (1), NO3 (2) and H2L=maleic acid

Two novel hydrogen maleato (HL) bridged Cu(II) complexes _∞¹[Cu(phen)Cl(HL)_2/2] 1 and _∞¹[Cu(phen)(NO₃)(HL)_2/2] 2 were obtained from reactions of 1,10-phenanthroline, maleic acid with CuCl₂·2H₂O and Cu(NO₃)₂·3H₂O, respectively, in CH₃OH/H₂O (1:1 v/v) at pH=2.0 and the crystal structures were determined by single crystal X-ray diffraction methods. Both complexes crystallize isostructurally in the monoclinic space group P2₁/n with cell dimensions: 1 a=8.639(2) Å, b=15.614(3) Å, c=11.326(2) Å, β=94.67(3)°, Z=4, D_calc=1.720 g/cm³ and 2 a=8.544(1) Å, b=15.517(2) Å, c=12.160(1) Å, β=90.84(8)°, Z=4, D_calc=1.734 g/cm³. In both complexes, the square pyramidally coordinated Cu atoms are bridged by hydrogen maleato ligands into 1D chains with the coordinating phen ligands parallel on one side. Interdigitation of the chelating phen ligands of two neighbouring chains via π–π stacking interactions forms supramolecular double chains, which are then arranged in the crystal structures according to pseudo 1D close packing patterns. Both complexes exhibit similar paramagnetic behavior obeying Curie–Weiss laws χ_m(T−θ)=0.414 cm³ mol⁻¹ K with the Weiss constants θ=−1.45, −1.0 K for 1 and 2, respectively.     

Micellar effects on photoinduced redox reactions of Fe(bpy)2(CN)2

Excitation of solutions of Fe(bipy)₂(CN)₂ by a 266-nm laser pulse produces a hydrated electron and the oxidized complex, Fe(bipy)₂ (CN)₂⁺, in the primary photochemical step, in homogeneous aqueous solution as well as in aqueous solutions containing cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) micelles. In all cases nascent hydrated electrons react with ground state Fe(bipy)₂(CN)₂ to form Fe(bipy)₂(CN)₂⁻, and comparison of the decay constants in the three media (H₂O: k = 2.8 × 10¹⁰ M⁻¹ s⁻¹; CTAB: k = 2.9 × 10¹⁰ M⁻¹ s⁻¹; SDS: k = 5.5 × 10⁹ M⁻¹ s⁻¹), shows that the reaction is essentially unaffected by CTAB micelles but is much slower in SDS solution. Similar micellar effects were found for the back reaction between e_aq⁻ and Fe(bpy)₂(CN)₂⁺. Rate constants for the scavenging of the photogenerated hydrated electrons by methyl viologen (MV²⁺) cations and NO₃⁻ anions were measured in the three systems, and the results indicate that for scavenging by MV²⁺ the rate constants are decreased in the micelle systems (k in H₂O, 8.4 × 10¹⁰; CTAB, 3.5 × 10¹⁰ and SDS, 1.58 × 10¹⁰ M⁻¹ s⁻¹), whereas for NO₃⁻ the CTAB micelle decreases while the SDS micelle enhances the scavenging compared to water solution (k in H₂O, 8.3 × 10⁹; CTAB, 7 × 10⁸; and SDS, 2.05 × 10¹⁰ M⁻¹ s⁻¹). For the comproportionation reaction between Fe(bipy)₂(CN)₂⁺ and Fe(bipy)₂(CN)₂⁻ both micelles reduce the rate (k in H₂O, 3.3 × 10¹⁰; CTAB, 2.3 × 10¹⁰; and SDS, 1.05 × 10¹⁰ M⁻¹s⁻¹), but while the reaction of Fe(bipy)₂(CN)₂⁺ with MV⁺ is increased in CTAB compared to water, it is slowed in SDS (k in H₂O, 2.4 × 10¹⁰; CTAB, 8.9 × 10¹⁰; and SDS, 1.8 × 10¹⁰ M⁻¹s⁻¹). All effects observed in these microheterogeneous systems can be uniformly interpreted in terms of Coulombic interactions between the actual reactants and the charged surface of the micelles.     

Electron transfer in organometallic clusters : XI. Redox chemistry of M3(CO)12(M = Ru, Os) and PPh3 derivatives; mechanism of catalysed nucleophilic substitution

The generality of a two-electron reduction process involving an mechanism has been established for M₃(CO)₁₂ and M₃(CO)₁₂−n(PPh₃)_n (M = Ru, Os) clusters in all solvents. Detailed coulometric and spectral studies in CH₂Cl₂ provide strong evidence for the formation of an ‘opened’ M₃(CO)₁₂²⁻ species the triangulo radical anions M₃(CO)₁₂^−· having a half-life of < 10⁻⁶ s in CH₂Cl₂. However, the electrochemical response is sensitive to the presence of water and is concentration dependent. An electrochemical response for “opened” M₃(CO)₁₂²⁻ is only detected at low concentrations < 5 × 10⁻⁴ mol dm⁻³ and under drybox conditions. The electroactive species ground at higher concentrations and in the presence of water M₃(CO)₁₁²⁻ and M₆(CO)₁₈²⁻ were confirmed by a study of the electrochemistry of these anions in CH₂Cl₂; HM₃(CO)₁₁⁻ is not a product. The couple [M₆(CO)₁₈]^−/2− is chemically reversible under certain conditions but oxidation of HM₃(CO)₁₁⁻ is chemically irreversible. Different electrochemical behaviour for Ru₃(CO)₁₂ is found when [PPN][X] (X = OAc⁻, Cl⁻) salts are supporting electrolytes. In these solutions formation of the ultimate electroactive species [μ-C(O)XRu₃(CO)₁₀]⁻ at the electrode is stopped under CO or at low temperatures but Ru₃(CO)₁₂^−· is still trapped by reversible attack by X presumably as [η¹-C(O)XRu₃(CO)₁₁]⁻. It is shown that electrode-initiated electron catalysed substitution of M₃(CO)₁₂ only takes place on the electrochemical timescale when M = Ru, but it is slow, inefficient and non-selective, whereas BPK-initiated nucleophilic substitution of Ru₃(CO)₁₂ is only specific and fast in ether solvents particulary THF. Metal---metal bond cleavage is the most important influence on the rate and specificity of catalytic substitution by electron or [PPN]-initiation. The redox chemistry of M₃(CO)₁₂ clusters (M = Fe, Ru, Os) is a consequence of the relative rates of metal---metal bond dissociation, metal-metal bond strength and ligand dissociation and in many aspects resembles their photochemistry.     

Homo- and hetero-bridged mixed-valence dinuclear complexes which contain the fragment ‘Rh(C6F5)3’

The reaction of the anionic mononuclear rhodium complex [Rh(C₆F₅)₃Cl(Hpz)]^t- (Hpz = pyrazole, C₃H₄N₂) with methoxo or acetylacetonate complexes of Rh or Ir led to the heterodinuclear anionic compounds [(C₆F₅)₃Rh(μ-Cl)(μ-pz)M(L₂)] [M = Rh, L₂ = cyclo-octa-1,5-diene, COD (1), tetrafluorobenzobarrelene, TFB (2) or (CO)₂ (4); M = Ir, L₂ = COD (3)]. The complex [Rh(C₆F₅)₃(Hbim)]⁻ (5) has been prepared by treating [Rh(C₆F₅)₃(acac)]⁻ with H₂bim (acac = acetylacetonate; H₂bim = 2,2′-biimidazole). Complex 5 also reacts with Rh or Ir methoxo, or with Pd acetylacetonate, complexes affording the heterodinuclear complexes [(C₆F₅)₃Rh(μ-bim)M(L₂)]⁻ [M = Rh, L₂ = COD (6) or TFB (7); M = Ir, L₂ = COD (8); M = Pd, L₂ = η³-C₃H₅ (9)]. With [Rh(acac)(CO)₂], complex 5 yields the tetranuclear complex [{(C₆F₅)₃Rh(μ-bim)Rh(CO)₂}₂]₂₋. Homodinuclear Rh^III derivatives [{Rh(C₆F₅)₃}₂(μ-L)₂]^·- [L₂ = OH, pz (11); OH, S^tBu (12); OH, SPh (13); bim (14)] have been obtained by substitution of one or both hydroxo groups of the dianion [{Rh(C₆F₅)₃(μ-OH)}₂]²⁻ by the corresponding ligands. The reaction of [Rh(C₆F₅)₃(Et₂O)_x] with [PdX₂(COD)] produces neutral heterodinuclear compounds [(C₆F₅)₃Rh(μ-X)₂Pd(COD)] [X = Cl (15); Br (16)]. The anionic complexes 1–14 have been isolated as the benzyltriphenylphosphonium (PBzPh₃⁺) salts.     

Thermal decomposition study on mixed ligand thymine complexes of divalent nickel(II) with dianions of some dicarboxylic acids

Thermal decomposition of mixed ligand thymine (2,4-dihydroxy-5-methylpyrimidine) complexes of divalent Ni(II) with aspartate, glutamate and ADA (N-2-acetamido)iminodiacetate dianions was monitored by TG, DTG and DTA analysis in static atmosphere of air. The decomposition course and steps of complexes [Ni(C₅H₆N₂O₂)(C₄H₅NO₄)²⁻(H₂O)₂]·H₂O, [Ni(C₅H₆N₂O₂)(C₅H₇NO₄)²⁻(H₂O)₂]·H₂O and [Ni(C₅H₆N₂O₂)(C₆H₈N₂O₅)²⁻(H₂O)₂]·1.5H₂O were analyzed. The final decomposition products are found to be the corresponding metal oxides. The kinetic parameters namely, activation energy (E*), enthalpy (ΔH*), entropy (ΔS*) and free energy change of decomposition (ΔG*) are calculated from the TG curves using Coats–Redfern and Horowitz–Metzger equations. The stability order found for these complexes follows the trend aspartate > ADA > glutamate.     

A spectroscopic study on the reaction-controlled phase transfer catalyst in the epoxidation of cyclohexene

The epoxidation of cyclohexene with hydrogen peroxide in a biphase medium (H₂O/CHCl₃) was carried out with the reaction-controlled phase transfer catalyst composed of quaternary ammonium heteropolyoxotungstates [π-C₅H₅N(CH₂)₁₅CH₃]₃[PW₄O₁₆]. A conversion of about 90% and a selectivity of over 90% were obtained for epoxidation of cyclohexene on the catalyst. The fresh catalyst, the catalyst under reaction conditions and the used catalysts were characterized by FT-IR, Raman and ³¹P NMR spectroscopy. It appears that the insoluble catalyst could degrade into smaller species, [(PO₄){WO(O₂)₂}₄]³⁻, [(PO₄){WO(O₂)₂}₂{WO(O₂)₂(H₂O)}]³⁻, and [(PO₃(OH)){WO(O₂)₂}₂]²⁻ after the reaction with hydrogen peroxide and becomes soluble in the CHCl₃ solvent. The active oxygen in the [W₂O₂(O₂)₄] structure unit of these soluble species reacts with olefins to form the epoxides and consequently the corresponding W---Ob---W (corner-sharing) and W---Oc---W (edge-sharing) bonds are formed. The peroxo group [W₂O₂(O₂)₄] can be regenerated when the W---Ob---W and W---Oc---W bonds react with hydrogen peroxide again. These soluble species lose active oxygen and then polymerize into larger compounds with the W---Ob---W and W---Oc---W bonds and then precipitate from the reaction solution after the hydrogen peroxide is consumed up. Part of the used catalyst seems to form more stable compounds with Keggin structure under the reaction conditions.     

The reactions of a dinuclear ferric complex (oxo) di-iron(III) triethylenetetraamminehexaacetate, Fe2O(ttha), with oxidizing and reducing free radicals. A pulse radiolysis study

The rate constants at which oxidizing and reducing radicals react with the dinuclear iron(III) complex Fe₂O(ttha)²⁻ were measured in neutral aqueous solution. The rate constants for reduction of the complex by ·CO₂^.− CH₃^.CHOH and O₂^.− were found to be comparable with rate constants previously measured in mononuclear iron(III) polyaminocarboxylate systems. Fe₂O(ttha)²⁻ reacts slowly with O₂^.− (k₈ = (1.2 ± 0.2) × 10⁴ dm³ mol⁻¹ s⁻¹) and, hence, is a relatively poor catalyst for the dismutation of superoxide radical. The hydrated electron reduces the complex at a diffusion-controlled rate in a process which consumes one proton: e_aq⁻ + Fe₂O(ttha)²⁻ → Fe₂^III,IIO(ttha)³⁻ The reduction by carbon-centered radicals produces a (III,II) mixed-valence complex with an absorption spectrum different from that of the Fe₂(II,III) species produced from reduction by the hydrated electron. The oxidizing radicals ^.OH and ·CO₃⁻ appear to act as reductants of the complex via ligand oxidation rather than by oxidation of the Fe₂^IIIO core to Fe₂^III,IVO. In the former case ligand attack appears to occur mainly at the methylene carbon of a glycinate group. The decarboxylation product, CO₂, was detected by its aquation reaction in the presence of a pH sensitive dye, bromthymol blue.     

Effect of high coverages on proton transfer in the zeolite/water system

The density functional theory and Hartree–Fock methods were used to investigate the proton transfer reaction for a series of model clusters of zeolite/(H₂O)_n; n=1,2,3, and 4. Without promoted water, the hydrogen-bonded dimer of the water/zeolite system exists as a simple hydrogen-bonded complex, ZOH.(H₂O)₂, and no proton transfer occurs from zeolite to water. The third promoted water, ZOH(H₂O)₂H₂O, was found to induce a pathway for proton transfer, but at least addition two promoted molecules, ZO(H₃O⁺)H₂O(H₂O)₂, must be involved for complete proton transfer from zeolite to H₂O. The results show that the hydronium ion in water cluster adsorbed on zeolite, ZO(H₃O⁺)(H₂O)₃, can considerably affect the structure and bonding of the hydrogen-bonded dimer of water. The OO distance is contracted from 2.818 Å found in the neutral complex, ZOH(H₂O)₄, to 2.777 Å for ion-pair complex, ZO(H₃O⁺)(H₂O)₃. The distance between the oxygen of the hydronium ion and the zeolitic acid site oxygen is predicted to be 2.480 Å which is in good agreement with the experimentally observed value of 2.510 Å. The corresponding density functional adsorption energy of the high coverages of adsorbing molecules on zeolite is calculated to be −9.14 kcal/mol per molecule at B3LYP/6-311+G(d,p) level of theory and compares well with the experimental observation of −8.20 kcal/mol.