The free amino acid tyrosine enhances the chlorinating activity of human myeloperoxidase

A key function of neutrophil myeloperoxidase (MPO) is the synthesis of hypochlorous acid (HOCl), a potent oxidizing agent that plays a cytotoxic role against invading bacteria and viruses at inflammatory sites and in phagosomes. MPO displayed a chlorinating activity preferably at acidic pH but at neutral pH MPO catalyzes mainly reactions of the peroxidase cycle. In the present work effects of tyrosine on the chlorinating activity of MPO were studied. At pH 7.4 we detected an increased HOCl production in the presence of tyrosine not only by the MPO-H₂O₂-Cl^- system but also in suspensions of zymosan-activated neutrophils. An excess of H₂O₂ is known to cause an accumulation of compound II of MPO blocking the generation of HOCl at neutral pH. As evidenced by spectral changes, tyrosine-induced activation of MPO to synthesize HOCl was due to the ability of tyrosine to reduce compound II back to the native state, thus accelerating the enzyme turnover. MPO-induced oxidation of tyrosine is relevant to what can be in vivo; we detected MPO-catalyzed formation of dityrosine in the presence of plasma under experimental conditions when tyrosine concentration was about three magnitudes of order less than the Cl⁻ concentration. At acidic pH formation of compound II was impaired in the presence of chloride and dityrosine couldn't be detected in plasma. In conclusion, the ability of tyrosine to increase the chlorinating activity of MPO at neutral pH and enhanced values of H₂O₂ may be very effective for the specific enhancement of HOCl production under acute inflammation.     

Synthesis of tantalum and niobium complexes that contain the diamidoamine ligand, [(3,4,5-F3C6H2NCH2CH2)2NMe], and the triamidoamine ligand, [(3,5-Cl2C6H3NCH2CH2)3N]

Several niobium and tantalum compounds were prepared that contain either the diamidoamine ligand, [(3,4,5-F₃C₆H₂NCH₂CH₂)₂NMe]²⁻ ([F₃N₂NMe]²⁻), or the triamidoamine ligand, [(3,5-Cl₂C₆H₃NCH₂CH₂)₃N]³⁻ ([Cl₂N₂NMe]³⁻). The former include [F₃N₂NMe]TaCl₃, [F₃N₂NMe]NbCl₃, [F₃N₂NMe]TaMe₃, [F₃N₂NMe]NbMe₃, [(F₃N₂NMe)TaMe₂][MeB(C₆F₅)₃], [F₃N₂NMe]Ta(CHSiMe₃)(CH₂SiMe₃), [F₃N₂NMe]Ta(CH₂-t-Bu)Cl₂, [F₃N₂NMe]Ta(CH-t-Bu)(CH₃), and [F₃N₂NMe]Ta(η²-C₂H₄)(CH₂CH₃). The latter include [Cl₂N₂NMe]TaCl₂, [Cl₂N₂NMe]TaMe₂, [Cl₂N₂NMe]Ta(η²-C₂H₄), and [Cl₂N₂NMe]Ta(η²-C₂H₂).X-ray diffraction studies were carried out on [F₃N₂NMe]Ta(CHSiMe₃)(CH₂SiMe₃), [F₃N₂NMe]Ta(η²-C₂H₄)(CH₂CH₃), and [Cl₂N₂NMe]TaMe_2..     

Conformational flexibility of 2,6-bis(pyrazol-1-ylmethyl)pyridine (L) in [(L)Co(H2O)3]Cl2 and [(L)Ni(H2O)2Cl]Cl·H2O. Molecular structures and non-covalent interactions

Using a non-planar tridentate ligand 2,6-bis(pyrazol-1-ylmethyl)pyridine (L⁵) two new coordination complexes [(L⁵)Co^II(H₂O)₃]Cl₂ (1) and [(L⁵)Ni^II(H₂O)₂Cl]Cl·H₂O (2) have been synthesized and structurally characterized. Complex 1 has N₃O₃ distorted octahedral environment around Co^II with coordination by L⁵ (two pyrazole and a pyridine nitrogen in a facial mode) and three water molecules. Complex 2 has N₃O₂Cl distorted octahedral geometry around Ni^II with meridional L⁵ coordination, two water molecules, and a Cl⁻ ion. Analysis of the crystal packing diagram reveals the involvement of solvent (water as metal-coordinated and as solvent of crystallization) and counteranion (Cl⁻) to play significant roles in generating 1D chains, involving O-H···Cl, and O-H···O interactions.     

New molybdenum(V) complexes based on the {Mo2O4} structural core with esters or anions of malonic and succinic acid

A series of malonato complexes of molybdenum(V) was prepared by reacting (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ or (PyH)_n[MoOBr₄]_n with malonic acid (H₂mal) or a half-neutralized acid, hydrogen malonate (Hmal⁻), at ambient conditions: (PyH)₃[Mo₂O₄Cl₄(μ₂-Hmal)] · CH₃CN (1), (PyH)₃[Mo₂O₄Br₄(μ₂-Hmal)] · CH₃CN (2), (PyH)₂[Mo₂O₄Cl(η²-mal)(μ₂-Hmal)Py] (3), (3,5-LutH)₂(H₃O) [Mo₂O₄(η²-mal)₂(μ₂-Hmal)] (4), (PyH)[Mo₂O₄Cl₂(μ₂-Memal)Py₂] (5), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-Memal)(3,5-Lut)₂] (6), (PyH)[Mo₂O₄Cl₂(μ₂-Etmal)Py₂] (7), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-Prmal)(3,5-Lut)₂] (8) and [{Mo₂O₄(μ₂-Memal)Py₂}₂(μ₂-OCH₃)₂] (9) (where Py = pyridine, C₅H₅N; PyH⁺ = pyridinium cation, C₅H₅NH⁺; 3,5-Lut = 3,5-lutidine, C₇H₉N; 3,5-LutH⁺ = 3,5-lutidinium cation, C₇H₉NH⁺; mal²⁻ = malonate, ⁻OOCCH₂COO⁻; Memal⁻ = monomethyl malonate, ⁻OOCCH₂COOCH₃; Etmal⁻ = monoethyl malonate, ⁻OOCCH₂COOC₂H₅ and Prmal⁻ = monopropyl malonate, ⁻OOCCH₂COOC₃H₇). The complex anions of compounds 1-8 have a common structural feature: a dinuclear, singly metal-metal bonded {Mo₂O₄}²⁺ core with the carboxylate moiety of the malonato ligand coordinated in a syn-syn bidentate bridging manner to the pair of metal atoms. The remaining four coordination sites of the {Mo₂O₄}²⁺ core are occupied with halides in 1 and 2, with halides/pyridine ligands in 5-8, with a pair of bidentate malonate ions in 4 and with the combination of all in 3. The neutral molecules of 9 consist of two {Mo₂O₄}²⁺ cores linked with a pair of methoxide ions into a chain-like, tetranuclear cluster. An esterification of malonic acid was observed to take place in the reaction mixtures containing alcohols. Solvothermal reactions with malonic acid carried out at 115 °C produced anionic acetato complexes as found in (PyH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)Py₂] · Py (10), (PyH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)Py₂] (11), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)(3,5-Lut)₂] (12) and (4-MePyH)₃[Mo₂O₄Cl₂(μ₂-OOCCH₃)(4-MePy)₂]₂Cl (13) (4-MePy = 4-methylpyridine, C₆H₇N). The acetate coordinated in the syn-syn bidentate bridging mode in all. Reactions of (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ with succinic acid (H₂suc) at ambient conditions resulted in a complex with a half-neutralized acid, (PyH)[Mo₂O₄Cl₂(μ₂-Hsuc)Py₂] · Py (14) (Hsuc⁻ = hydrogen succinate, ⁻OOC(CH₂)₂COOH), while those carried out at 115 °C in a tetranuclear succinato complex, (4-MePyH)₂[{Mo₂O₄Cl₂(4-MePy)₂}₂(μ₄-suc)] (15) (suc²⁻ = succinate, ⁻OOC(CH₂)₂COO⁻). The tetranuclear anion of 15 consists of two {Mo₂O₄}²⁺ cores covalently linked with a tetradentate succinato ligand. The compounds were fully characterized by infrared vibrational spectroscopy, elemental analyses and X-ray diffraction studies.     

No or little production of singlet molecular oxygen in HOCl or HOClH2O2 a model system for myeloperoxidase/H2O2/Cl−

The HOCl in chlorine-water oxidizes DPF to cis-DBE in parallel to the HOCl concentration. The addition of H₂O₂ produces singlet molecular oxygen, and a bimol collision above pH 6.0, but not in the pH region 3.0 to 4.0. The DPF conversion to cis-DBE is initiated by a 1,2-position attack of OH^? and Cl⁺, followed by the HCl elimination. The oxidation potency of HOCl is much greater than the singlet molecular oxygen generated in chlorine-water/H₂O₂ solution, on the pH range 6.0 to 8.0 where both HOCl and OCl^? are present.     

Hydrothermal synthesis and structure of [Ni(tpyrpyz)2]2[Mo4O12F2][Mo6O19] · 2H2O, a material exhibiting an unusual tetranuclear polyoxofluoromolybdate cluster [Mo4O12F2]

The hydrothermal reaction of a solution of Ni(CH₃CO₂)₂ · 4H₂O, MoO₃, tetra-4-pyridylpyrazine, H₂O₃PCH₃, and HF at 200 °C for 96 h yields orange crystals of [Ni(tpyrpyz)₂]₂[Mo₄O₁₂F₂][Mo₆O₁₇] · 2H₂O (1 · 2H₂O). The structure consists of discrete {Ni(tpyrpyz)₂}²⁺ cations and {Mo₆O₁₉}²⁻ and {Mo₄O₁₂F₂}²⁻ anionic clusters. The hexamolybdate is the well-documented octahedron of octahedra, that is, six {MoO₆} octahedra in a compact edge-sharing arrangement. The novel oxyfluoride cluster {Mo₄O₁₂F₂}²⁻ features two {MoO₄F₂} octahedra, sharing the edge defined by the fluoride ligands; the octahedral Mo sites corner-share to two {MoO₄} tetrahedra in the μ₂-O, O^′ bridging mode.     

Synthesis and structure of a lead(II)-citrate: {Na(H2O)3}[Pb5(C6H5O7)3(C6H6O7)(H2O)3]·9.5H2O

The reaction of lead(II) nitrate with trisodium citrate Na₃(C₆H₅O₇) in a 1:22.5 ratio at pH 4.8 provides crystals of {Na(H₂O)₃}[Pb₅(H₂O)₃(C₆H₅O₇)₃(C₆H₆O₇)]·9.5H₂O (1). The structure of 1 is two-dimensional and exhibits five distinct Pb(II) sites and four different modes of citrate bonding. The five lead sites all display hemidirected coordination geometries, that is, irregular distribution of neighboring oxygen atoms resulting in obvious gaps in the coordination spheres. Consequently, the lead coordination geometries exhibit proximal bonding to a number of oxygen donors, as well as distal interactions with nearest neighbors. The coordination numbers vary from 8 to 10, with ‘5+3’, ‘5+4’, ‘6+4’ and ‘7+3’ coordination modes where the first number refers to the proximal ligands and the second to the distal set. The four crystallographically distinct citrate groups include three with deprotonated carboxylate groups (C₆H₅O₇)³⁻ and one with a single protonated carboxyl group (C₆H₆O₇)². The citrate ligands bridge 3, 5, 7 and 7 lead sites. Three of the citrate groups exhibit tridentate chelation coordination to a lead site through two carboxylate oxygen donors and the hydroxyl groups. One citrate group projects an uncoordinated -OH group and a pendant protonated carboxyl group into the interlamellar domain. This latter carboxyl group coordinates to a sodium cation, which exhibits five coordinate geometry defined by three aqua ligands and the carbonyl oxygen of the -CO₂H groups in the basal plane and a citrate -OH donor in the apical position.     

Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3] and Pt(R2SO)2Cl2

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (¹⁹⁵Pt, ¹H and ¹³C). In ¹⁹⁵Pt NMR, the chloro ionic compounds have shown signals between −2979 and −3106 ppm, while the cis disubstituted complexes were observed at higher fields, between −3450 and −3546 ppm. The signal of the compound trans-Pt(DPrSO)₂Cl₂ was found at higher field (−3666 ppm) than its cis analogue (−3517 ppm), since π-back-donation is considerably less effective in the trans geometry. In ¹H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl₃]⁻, but for the other more sterically hindered ligands, two series of resonances were observed for the protons in α and β positions. The coupling constant ³J(¹⁹⁵Pt-¹H) are between 15 and 33 Hz. The ¹³C NMR results were interpreted in relation to the concept of inversed polarization of the π sulfoxide bond. The ²J(¹⁹⁵Pt-¹³C) values vary between 35 and 66 Hz, while a few ³J(¹⁹⁵Pt-¹³C) couplings were observed (13-26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)₄[Pt(TMSO)Cl₃], N(Me)₄[Pt(DPrSO)Cl₃], K[Pt(EMSO)Cl₃], K[Pt(TMSO)Br₃] · H₂O and N(Et)₄[Pt(DPrSO)Br₃] and one disubstituted complex cis-Pt(DBuSO)₂Cl₂ were determined. The trans influence of the different ligands is discussed.     

Zirconium and hafnium aqua complexes [(H2O)3M(P2W17O61)]: Synthesis, characterization and substitution of water by chiral ligand

The hydroxocomplexes [{(H₂O)M(μ₂-OH)(P₂W₁₇O₆₁)}₂]¹⁴⁻ (M = Zr, Hf) in HCl undergo cleavage of the hydroxo bridges with the formation of monomeric species [(H₂O)₃M(P₂W₁₇O₆₁)]⁶⁻. In the case of Hf single crystals of the composition (Me₂NH₂)_5.5(H)_1.5[(Hf(H₂O)₃)_0.9(WO)_0.1{P₂W₁₇O₆₁}]Cl·9.5H₂O (1), as the result of co-crystallization of [(H₂O)₃Hf(P₂W₁₇O₆₁)]⁶⁻ and [P₂W₁₈O₆₂]⁶⁻ salts, were isolated from these solutions and structurally characterized. Zr gives (Me₂NH₂)₂(H)₄[{(H₂O)₂ZrP₂W₁₇O₆₁}]·8.67H₂O (2), in whose structure chiral polymeric chains {[(H₂O)₂M(P₂W₁₇O₆₁)]}_n⁶ⁿ⁻ are present. Under hydrothermal conditions the water molecules in [(H₂O)₃M(P₂W₁₇O₆₁)]⁶⁻ are replaced by l-malic acid with the formation of stable chiral polyoxoanions, isolated as (NH₂Me₂)₈[M(L-ООССН(ОН)СН₂СОО)P₂W₁₇O₆₁]·7·9H₂O (M = Zr, 3; M = Hf, 4). The structures of 1, 2 and 3 were determined; 3 and 4 were found to be isostructural. The products were also characterized by elemental analysis, thermogravimetry and IR-spectroscopy.     

Chemiluminescent determination of H2O2 using 4-(1,2,4-triazol-1-yl)phenol as an enhancer based on the immobilization of horseradish peroxidase onto magnetic beads

This article describes the employment of a novel p-phenol derivative, 4-(1,2,4-triazol-1-yl)phenol (TRP), as a highly potent signal enhancer of the luminol-hydrogen peroxide (H₂O₂)-horseradish peroxidase (HRP) chemiluminescence (CL) system. The CL reaction conditions were optimized, and the enhancement characteristics of TRP were compared with those of p-iodophenol (PIP). TRP produced a strong enhancement of the CL with the effect of prolonging the light emission. The developed system was then applied to the determination of H₂O₂ with immobilized HRP using magnetic beads as a solid support. The linear range for H₂O₂ was 2.0 × 10⁻⁶ to 1.0 × 10⁻³ M. The detection limit for H₂O₂ was 2.0 × 10⁻⁶ M. The proposed sensor was applied successfully to the determination of H₂O₂ in rainwater.     

Interactions of tertiary phosphines with p-benzoquinones; X-ray structures of [HO(CH2)3]3PC6H2(O)(OH)(MeO) and Ph3PC6H3(O)(OH)

Phosphonium zwitterions of a known type were obtained in high yield via a 1:1 reaction of p-benzoquinone or methoxy-p-benzoquinone with the tertiary phosphines R₃P [R = (CH₂)₃OH, Ph, Et, Me] and Ph₂MeP, in acetone or benzene at room temperature. In all cases, attack of the P-atom occurs at a C-atom rather than at an O-atom. The products were characterized to various degrees by elemental analysis, ³¹P{¹H}, ¹H and ¹³C NMR spectroscopies, and mass spectrometry, and two of the zwitterions, the new [HO(CH₂)₃]₃P⁺C₆H₂(O⁻)(OH)(MeO) and the known Ph₃P⁺C₆H₃(O⁻)(OH), were structurally characterized by X-ray analysis. The PEt₃ reaction also produces small amounts of the ‘dimeric’, μ-oxo co-product Et₃P⁺C₆H₂(O⁻)(OH)-O-C₆H₃(O⁻)P⁺Et₃ that is tentatively characterized by 1D- and 2D-NMR data. 2,5-Di-tert-butyl- and 2,3,5,6-tetramethyl-p-benzoquinone do not react with [HO(CH₂)₃]₃P under the conditions noted above. Heating D₂O solutions of the water-soluble zwitterions R₃P⁺C₆H₃(O⁻)(OH) [R = (CH₂)₃OH, Et] at 90 °C for 72 h leads to complete H/D exchange of the H-atom in the position ortho to the phosphonium center.     

H2O2 reactivity of a dinuclear copper(II) complex incorporating a constrained binucleating polyaminopyridyl ligand and a phosphodiester coligand

A dinuclear copper(II) complex [Cu₂(PD)(DPP⁻)₂](ClO₄)₂ (1) incorporating a constrained binucleating hexadenate ligand, PD (1,3-bis{bis[(2-pyridyl)ethyl]amino}benzene), and coligand, DPP⁻ (diphenylphosphate) was synthesized and characterized, with a specific outlook towards evaluating spectroscopic and H₂O₂ reactivity relevant to the active-sites of noncoupled dinuclear copper enzymes, DβM and PHM. In solution, complex 1 exhibits a broad ¹H NMR in the range −25 to +60 ppm and has a solution magnetic moment (μ) of ∼2.0 B.M./Cu(II), typical of a noninteracting dicopper(II) center. The room temperature H₂O₂ reactivity of 1 monitored by UV-Vis spectroscopy reveals the formation of a copper(II)-dioxygen intermediate 1a, which in turn leading to a arene ligand hydroxylation (PD-O⁻) and thus provide a new doubly-bridged dicopper(II) complex, [Cu₂(PD-O⁻)(DPP⁻)](ClO₄)₂ (2). The dioxygen intermediate produces OPPh₃ on treatment with PPh₃ revealing it is an electrophilic hydroperoxide oxidant. Solution magnetic moment of 1.61 B.M./Cu(II) indicates the product complex 2 is a moderately interacting dicopper(II) center and its ¹H NMR spans between −20 and +180 ppm. A comparison of the optical absorption features of complex 1a with related dinuclear hydroperoxo-copper(II) complexes is discussed.     

Determination of H2O2-dependent generation of singlet oxygen from human saliva with a novel chemiluminescence probe

Singlet oxygen (¹O₂) has been shown to play an important role in salivary defense system, but its generation process and level from human saliva remain uncertain due to the lack of a reliable detection method. We have previously reported 4,4′(5′)-bis[2-(9-anthryloxy)ethylthio]tetrathiafulvalene (BAET) as a novel chemiluminescence probe for ¹O₂. In this work, the probe is successfully used to characterize H₂O₂-dependent generation of ¹O₂ from saliva in real time. However, the yield of ¹O₂ is found to be very low, for example, being about 0.13 nmol from 200 μL saliva in the presence of 1 mM of hydrogen peroxide over a 5-s reaction period. The result is also compared with that obtained with another ¹O₂ probe 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (CLA), demonstrating that, besides ¹O₂, the other reactive oxygen species such as hydroxyl radical may also be involved in the reaction of saliva with H₂O₂. Furthermore, the present study shows that the selectivity of BAET for ¹O₂ is much higher than that of CLA and thus BAET is highly suited for the detection of ¹O₂ in the presence of other reactive oxygen species in biological systems.     

Synthesis, crystal structure and vibrational spectroscopy of a novel mixed ligands Ni(II) pentaborate: [Ni(C4H10N2)(C2H8N2)2][B5O6(OH)4]2

A novel organic-inorganic hybrid pentaborate [Ni(C₄H₁₀N₂)(C₂H₈N₂)₂][B₅O₆(OH)₄]₂ has been synthesized by hydrothermal reaction and characterized by FT-IR, Raman spectroscopy, elemental analyses and DTA-TGA. Its crystal structure was determined from single crystal X-ray diffraction. The structure consists of isolated polyborate anion [B₅O₆(OH)₄]⁻ and nickel complex cation of [Ni(C₄H₁₀N₂)(C₂H₈N₂)₂]²⁺, in which the two kinds of ligands come from the decomposition of triethylenetriamine material. The [B₅O₆(OH)₄]⁻ units are connected to one another through hydrogen bonds, forming a three-dimensional framework with large channel along the a and c axes, in which the templating [Ni(C₄H₁₀N₂)(C₂H₈N₂)₂]²⁺ cations are located. The assignments of the record FT-IR absorption frequencies and Raman shifts were given.     

Preparation, crystal structure and magnetic property of a binuclear oxalate-bridged iron(III) compound: Fe2(C2O4)Cl4(DMF)4 (DMF = dimethylformamide)

An oxalato-bridged binuclear iron(III) compound, Fe₂(C₂O₄)Cl₄(DMF)₄ (DMF = dimethylformamide), was obtained by electrocrystallization for three weeks at 3.4 V and it displays a strong antiferromagnetic interaction of J = −6.74(4) cm⁻¹.     

Rb2[B12(OH)12]·2H2O and Rb2[B12(OH)12]·2H2O2: Hydrate and perhydrolate of rubidium dodecahydroxo-closo-dodecaborate

The orthorhombically crystallizing salts Rb₂[B₁₂(OH)₁₂]·2H₂O (a = 1576.81(9), b = 813.08(5), c = 1245.32(7) pm) and Rb₂[B₁₂(OH)₁₂]·2H₂O₂ (a = 1616.54(9), b = 814.29(5), c = 1260.12(7) pm) could be prepared from Rb₂[B₁₂H₁₂] and hydrogen peroxide. Both crystal structures were determined by X-ray single crystal diffraction and refined in the space group Cmce. They are not isostructural to the other compounds containing icosahedral dodecahydroxo-closo-dodecaborate dianions [B₁₂(OH)₁₂]²⁻ and potassium, rubidium or cesium cations already known to literature, but both title compounds crystallize quasi-isotypically exhibiting Rb⁺ cations in 10-fold oxygen coordination. The hydrogen peroxide adduct (Rb₂[B₁₂(OH)₁₂]·2H₂O₂) is explosive on shock and heat, while the hydrate (Rb₂[B₁₂(OH)₁₂]·2H₂O) is not.     

Selective synthesis of triangular cluster oxido-sulfidocomplexes of Mo and W: High yield preparations of [Mo3O2S2(H2O)9], [W3O2S2(H2O)9], [W2MoO2S2(H2O)9] and their derivatization

Reaction of [Mo₂O₂(μ-S)₂(H₂O)₆]²⁺ with Mo(CO)₆ or metallic Mo under hydrothermal conditions (140 °C, 4 M HCl) gives oxido-sulfido cluster aqua complex [Mo₃(μ₃-S)(μ-O)₂(μ-S)(H₂O)₉]⁴⁺ (1). Similarly, [W₃(μ₃-S)(μ-O)₂(μ-S)(H₂O)₉]⁴⁺ (2) is obtained from [W₂O₂(μ-S)₂(H₂O)₆]²⁺ and W(CO)₆. While reaction of [Mo₂O₂(μ-S)₂(H₂O)₆]²⁺ with W(CO)₆ mainly proceeds as simple reduction to give 1, [W₂O₂(μ-S)₂(H₂O)₆]²⁺ with Mo(CO)₆ produces new mixed-metal cluster [W₂Mo(μ₃-S)(μ-O)₂(μ-S)(H₂O)₉]⁴⁺ (3) as main product. From solutions of 1 in HCl supramolecular adduct with cucurbit[6]uril (CB[6]) {[Mo₃O₂S₂(H₂O)₆Cl₃]₂CB[6]}Cl₂⋅18H₂O (4) was isolated and structurally characterized. The aqua complexes were converted into acetylacetonates [M₃O₂S₂(acac)₃(py)₃]PF₆ (M₃ = Mo₃, W₃, W₂Mo; 5a-c), which were characterized by X-ray single crystal analysis, electrospray ionization mass spectrometry and ¹H NMR spectroscopy. Crystal structure of (H₅O₂)(Me₄N)₄[W₃(μ₃-S)(μ₂-S)(μ₂-O)₂(NCS)₉] (6), obtained from 2, is also reported.     

Raman and infrared spectroscopic and theoretical studies of dinuclear rhenium and osmium complexes, M2(O2CCH3)4X2 (M = Re, Os; X = Cl, Br)

Infrared, far-infrared and Raman spectra of Re₂(O₂CCH₃)₄X₂ (X = Cl, Br) and Re₂(O₂CCD₃)₄Cl₂ have been recorded. Assignments of the vibrational spectra of Os₂(O₂CCH₃)₄Cl₂ and its deuterated derivative have been completed together with the Re complexes on the basis of normal-coordinate analysis. Force constant calculation was made for the acetate ion as well as for a four-atomic unit (with the CH₃ and CD₃ groups considered as point masses) using optimized masses of 16.7, 17.8, 20.5 and 21.6 for ¹²CH₃, ¹³CH₃, ¹²CD₃ and ¹³CD₃ groups, respectively. The force constants of the acetate ion have been adopted to the starting force field of the M₂(O₂CCH₃)₄X₂ type complexes. The metal-halide (0.889, 0.997 and 1.286 N cm⁻¹) and metal-metal stretching (3.32, 3.34 and 3.57 N cm⁻¹) force constants were obtained for Re₂(O₂CCH₃)₄Cl₂Re₂(O₂CCH₃)₄Br₂ and Os₂(O₂CCH₃)₄Cl₂ complexes, respectively. It was shown that the so-called diatomic approximation in most cases overestimates the M-M stretching force constants by 30-40%. Much better correlation has been obtained to fit these force constants, which produced values very close to those obtained by full normal-coordinate calculations. The Re-Re stretching force constants showed a reasonable correlation with the Re-Re bond distances for 18 rhenium complexes.     

Structure and reactivity of [Ru(2,3-Medpp)2Cl2]

The structure and reactivity of the complex [Ru(2,3-Medpp)₂Cl₂](PF₆)₂ (2,3-Medpp⁺=2-[2-(1-methylpyridiniumyl)]-3-(2-pyridyl)pyrazine) was investigated by X-ray diffraction (XRD), ¹H NMR, redox, and UV-Vis absorption measurements. X-ray analysis shows that crystals obtained from an acetonitrile-toluene solution contain the trans-Cl₂, trans-pyrazine isomeric form, while ¹H NMR and redox measurements on the main product of the synthetic workup indicate the presence of the trans-Cl₂, cis-pyrazine isomer. In the dark at 70 °C, the complex [Ru(2,3-Medpp)₂Cl₂]²⁺ reacts slowly in acetonitrile isomerizing to the cis-[Ru(2,3-Medpp)₂(CH₃CN)Cl]³⁺ species. Under ambient light in the presence of excess AgNO₃ the cis-[Ru(2,3-Medpp)₂(CH₃CN)₂]⁴⁺ species is obtained.     

Synthesis, crystal structure and magnetic properties of a chain coordination polymer {[Cu4L2(H2O)] · H2O}n

A chain coordination polymer with the chemical formula {[Cu₄L₂(H₂O)] · H₂O}_n, has been synthesized by the assembly reaction of K₂CuL · 1.5H₂O and Cu(OAC)₂ · H₂O with a 1:1 mole ratio in methanol, where H₄L = 2-hydroxy-3-[(E)-({2-[(2-hydroxybenzoyl)imino]ethyl}imino)methyl] benzoic acid, OAC⁻ = CH₃COO⁻. The crystal structure was determined by single-crystal X-ray diffraction analysis, the compound has chain molecular structure formed by dissymmetrical tetranuclear units. The magnetic measurements showed that Cu-Cu of the complex exhibit antiferromagnetic interactions, and satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a binuclear system, and further using molecular field approximation to deal with magnetic exchange interactions between binuclear systems.