Functionalization of hafnium oxamidide complexes prepared from CO-induced N2 cleavage

Functionalization of the nitrogen atoms in the hafnocene oxamidide complexes [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf](2)(N(2)C(2)O(2)) and [(η(5)-C(5)Me(4)H)(2)Hf](2)(N(2)C(2)O(2)), prepared from CO-induced N(2) bond cleavage, was explored by cycloaddition and by formal 1,2-addition chemistry. The ansa-hafnocene variant, [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf](2)(N(2)C(2)O(2)), undergoes facile cycloaddition with heterocumulenes such as (t)BuNCO and CO(2) to form new N-C and Hf-O bonds. Both products were crystallographically characterized, and the latter reaction demonstrates that an organic ligand can be synthesized from three abundant and often inert small molecules: N(2), CO, and CO(2). Treatment of [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf](2)(N(2)C(2)O(2)) with I(2) yielded the monomeric iodohafnocene isocyanate, Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf(I)(NCO), demonstrating that C-C bond formation is reversible. Alkylation of the oxamidide ligand in [(η(5)-C(5)Me(4)H)(2)Hf](2)(N(2)C(2)O(2)) was explored due to the high symmetry of the complex. A host of sequential 1,2-addition reactions with various alkyl halides was discovered and both N- and N,N'-alkylated products were obtained. Treatment with Br?nsted acids such as HCl or ethanol liberates the free oxamides, H(R(1))NC(O)C(O)N(R(2))H, which are useful precursors for N,N'-diamines, N-heterocyclic carbenes, and other heterocycles. Oxamidide functionalization in [(η(5)-C(5)Me(4)H)(2)Hf](2)(N(2)C(2)O(2)) was also accomplished with silanes and terminal alkynes, resulting in additional N-Si and N-H bond formation, respectively.     

一种红光发射的粘度荧光探针

以三苯胺和苯并噻唑盐为原料,设计合成了一种具有红光发射特性的D-π-A型荧光粘度探针N-乙酸乙酯基-2-(4-甲酸甲酯基三苯胺-4'-乙烯基)苯并噻唑六氟磷酸盐(L),运用现代分析测试手段进行了系统地表征。 研究结果表明,探针L的最大发射波长为630 nm,能有效地降低生物背景,提高生物成像的信噪比。 该探针对粘度有很好的荧光响应,其荧光强度比值(I/I₀)的对数与粘度的对数呈现很好的线性关系(R²=0.9934)。 此外,探针L对极性的敏感性小,且荧光信号不受生物分子的干扰。 生物学研究结果表明,探针L具有低的细胞毒性,可应用于细胞内微环境粘度的荧光成像。     

Photodissociation channels for N2O near 130 nm studied by product imaging

The photodissociation of N(2)O at wavelengths near 130 nm has been investigated by velocity-mapped product imaging. In all, five dissociation channels have been detected, leading to the following products: O((1)S)+N(2)(X (1)Sigma), N((2)D)+NO(X (2)Pi), N((2)P)+NO(X (2)Pi), O((3)P) + N(2)(A (3)Sigma(+) (u)), and O((3)P) + N(2)(B (3)Pi(g)). The most significant channel is to the products O((1)S) + N(2)(X(1)Sigma), with strong vibrational excitation in the N(2). The O((3)P) + N(2)(A,B):N((2)D,(2)P) + NO branching ratio is measured to be 1.4 +/- 0.5, while the N(2)(A) + O((3)P(J)):N(2)(B) + O((3)P(J)) branching ratio is determined to be 0.84+/-0.09. The spin-orbit distributions for the O((3)P(J)), N((2)P(J)), and N((2)D(J)) products were also determined. The angular distributions of the products are in qualitative agreement with excitation to the N(2)O(D (1)Sigma(+)) state, with participation as well by the (3)Pi(v) state.     

Synthesis and characterization of ultrathin multilayer films based on molybdenum polyoxometalate (Mo(54))

The crown-shaped molybdenum polyoxometalate cluster Na(26)[[Na(H(2)O)(2)](6)[(micro(3) -OH)(4) (Mo(20)(V)), (Mo(34)(VI)(O)(164) (micro-CH(3)COO(4)) x 120H(2)O(Mo(54)) was synthesized and first used as a bulk modifier to fabricate a three-dimensional modified WIGE electrode by the layer-by-layer method. The (Mo(54))/PAH)(n) multilayer films have been characterized by X-ray photoelectron spectra (XPS) and atomic force microscopy (AFM). UV-vis measurements reveal regular film growth with each Mo(54) adsorption. The electrochemical method was used to characterize the modified WIGE electrode, which is important for practical applications.     

Hofmeister effects on electron-transfer reactions of 1-pyrenesulfonic acid radical cation with nucleophilic anions in Nafion membranes

The electron-transfer reaction from nucleophilic anions such as SCN(-), N(3)(-), I(-), and Br(-) to the 1-pyrenesulfonic acid radical cation (Py(*+)SA(-)) generated via a resonant two-photon ionization process in the Nafion membranes was investigated with transient absorption measurements. The apparent quenching rates observed in the Nafion membrane (k(q)(Nf)) were almost 2-4 orders smaller than those observed in the bulk solutions (k(q)(bulk)). The attenuation factor (AF), which is defined as log(k(q)(Nf)/k(q)(bulk)), decreased in the order SCN(-) > N(3)(-) > I(-) > Br(-). This interesting behavior was interpreted in terms of the anionic Hofmeister effects. The effects of hydrophobic organic cations such as tetrabutylammonium ion (Bu(4)N(+)) and tetraethylammonium ion (Et(4)N(+)) exchanged into the Nafion membranes were also examined.     

Synthesis, characterizations and luminescent properties of three novel aryl amide type ligands and their lanthanide complexes

Three new aryl amide type ligands, N-(phenyl)-2-(quinolin-8-yloxy)acetamide (L(1)), N-(benzyl)-2-(quinolin-8-yloxy)acetamide (L(2)) and N-(naphthalene-1-yl)-2-(quinolin-8-yloxy)acetamide (L(3)) were synthesized. With these ligands, three series of lanthanide(III) complexes were prepared: [Ln(L(1))(2)(NO(3))(2)]NO(3), [Ln(L(2))(2)(NO(3))(2)(H(2)O)(2)]NO(3).H(2)O and [Ln(L(3))(2)(NO(3))(2)(H(2)O)(2)]NO(3).H(2)O (Ln=La, Sm, Eu, Gd). The complexes were characterized by the elemental analyses, molar conductivity, (1)H NMR spectra, IR spectra and TG-DTA. The fluorescence properties of complexes in the solid state and the triplet state energies of the ligands were studied in detail, respectively. It was found that the Eu(III) complexes have bright red fluorescence in solid state. The energies of excited triplet state for the three ligands are 20325 cm(-1) (L(3)), 21053 cm(-1) (L(2)) and 22831 cm(-1) (L(1)), respectively. All the three ligands sensitize Eu(III) strongly and the order of the emission intensity for the Eu(III) complexes with the three ligands is L(3)>L(2)>L(1). It can be explained by the relative energy gap between the lowest triplet energy level of the ligand (T) and (5)D(1) of Eu(III). This means that the triplet energy level of the ligand is the chief factor, which dominates Eu(III) complexes luminescence.     

Synthesis and Crystal Structure of [Cu(phen)2(SO4)(H2O)]·0.5C4H4O4·7H2O

The title compound, [Cu(phen)2(SO4)(H2O)]·0.5C4H4O4·7H2O (phen = 1,10-phe-nanthroline and C4H4O4 = fumaric acid), has been synthesized and characterized by single-crystal X-ray diffraction. The crystal is of triclinic, space group P with a = 11.4827(2), b = 11.9086(2), c = 13.77350(10)(A), α = 80.6830(10), β = 66.6480(10), γ = 64.0480(10)o, V = 1554.63(4) (A)3, Mr = 722.17, Z = 2, Dc = 1.543 g/cm3, μ = 0.845 mm-1, F(000) = 750, R = 0.0349 and wR = 0.0837 for 4754 observed reflections (I > 2σ(I)). The compound contains a six-coordinated copper(II) center, which is surround by four N atoms of two phen ligands (Cu-N distances in the range of 1.997(2)～2.225(2)(A)), one sulfate O atom (Cu-O = 2.0037(17) (A)) and one water O atom (Cu-O(5w) = 2.719(2) (A)) in a distorted octahedral geometry. Extensive hydrogen-bonding interactions are involved in water molecules, ligated sulfate anions and fumaric acid molecules. In addition, π-π interactions via aromatic nitrogen-containing ligands are also discussed. The combination of non-covalent interactions leads to the formation of a 3-D network structure.     

Aggregation control by homologous tripodal tetradentate amino acid ligands in oxo-bridged diiron(III) aquo complexes

Isoelectronic oxo-bridged diiron(III) aquo complexes of the homologous tripodal tetradentate amino acid ligands, N,N'-bis(2-pyridylmethyl)-3-aminoacetate (bpg(-)) and N,N'-bis(2-pyridylmethyl)-3-aminopropionate (bpp(-)), containing [(H(2)O)Fe(III)-(mu-O)-Fe(III)(H(2)O)](4+) cores, oligomerise, respectively, by dehydration and deprotonation, or by dehydration only, in reversible reactions. In the solid state, [Fe(2)(O)(bpp)(2)(H(2)O)(2)](ClO(4))(2) (1(ClO(4))(2)) exhibits stereochemistry identical to that of [Fe(2)(O)(bpg)(2)(H(2)O)(2)](ClO(4))(2) (2(ClO(4))(2)), with the ligand carboxylate donor oxygen atoms and the water molecules located cis to the oxo bridge and the tertiary amine group trans to it. Despite their structural similarity, 1(2+) and 2(2+) display markedly different aggregation behaviour in solution. In the absence of significant water, 1(2+) dehydrates and dimerises to give the tetranuclear complex, [Fe(4)(O)(2)(bpp)(4)](ClO(4))(4) (3(ClO(4))(4)), in which the carboxylate groups of the four bpp(-) ligands act as bridging groups between two [Fe(2)(O)(bpp)(2)](2+) units. Under similar conditions, 2(2+) dehydrates and deprotonates to form dinuclear and trinuclear oligomers, [Fe(2)(O)(OH)(bpg)(2)](ClO(4)) (4ClO(4)) and [Fe(3)(O)(2)(OH)(bpg)(3)](ClO(4)) (5(ClO(4))), related by addition of 'Fe(O)(bpg)' units. The trinuclear 5(ClO(4)), characterised crystallographically as two solvates 5(ClO(4)).3H(2)O and 5(ClO(4)).2MeOH, is based on a hexagonal [Fe(3)(O)(2)(OH)(bpg)(3)](+) unit, formally containing one hydroxo and two oxo bridges. The different aggregation behaviour of 1(ClO(4))(2) and 2(ClO(4))(2) results from the difference of one methylene group in the pendant carboxylate arms of the amino acid ligands.     

Magneto-structural studies on heterobimetallic malonate-bridged M(II)Re(IV) complexes (M = Mn, Co, Ni and Cu)

The mononuclear Re(IV) compound of formula (PPh(4))(2)[ReBr(4)(mal)] (1) was used as a ligand to obtain the heterobimetallic species [ReBr(4)(μ-mal)Co(dmphen)(2)]· MeCN (2), [ReBr(4)(μ-mal)Ni(dmphen)(2)] (3), [ReBr(4)(μ-mal)Mn(dmphen)(2)] (4a), [ReBr(4)(μ-mal)Mn(dmphen)(H(2)O)(2)]·dmphen·MeCN·H(2)O (4b), [ReBr(4)(μ-mal)Cu(phen)(2)]·1/4H(2)O (5) and [ReBr(4)(μ-mal)Cu(bipy)(2)] (6) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline, phen = 1,10-phenanthroline and bipy = 2,2'-bipyridine). The structures of 2 and 5 (single-crystal X-ray diffraction) are made up of neutral [ReBr(4)(μ-mal)M(AA)] dinuclear units [AA = dmphen with M = Co (2) and AA = phen with M = Cu (5)] where the metal ions are connected through a malonate ligand which exhibits simultaneously the bidentate [at the Re(IV)] and monodentate [at the M(II)] coordination modes. The carboxylate-malonate group in them adopts the anti-syn conformation with intramolecular ReM separation of 5.098(8) (2) and 4.947(2) ? (5). The magnetic properties of 1-6 were investigated in the temperature range 1.9-295 K. The magnetic behaviour of 1 is the expected for a magnetically isolated Re(IV) complex with a large value of the zero-field splitting (2D ca. -70 cm(-1)) whereas weak antiferromagnetic interactions between Re(IV) and M(II) are observed in the heterobimetallic compounds 2 (J = -0.63 cm(-1)), 3 (J = -1.37 cm(-1)), 4a (J = -1.29 cm(-1)), 5 (J = -1.83 cm(-1)) and 6 (J = -0.26 cm(-1)). Remarkably, 4b behaves as a ferrimagnetic chain with regular alternating Re(IV) and Mn(II) cations (J = -2.64 cm(-1)).     

Complexes of HNO3 and NO3 - with NO2 and N2O4, and their potential role in atmospheric HONO formation

Calculations were performed to determine the structures, energetics, and spectroscopy of the atmospherically relevant complexes (HNO(3)).(NO(2)), (HNO(3)).(N(2)O(4)), (NO(3)(-)).(NO(2)), and (NO(3)(-)).(N(2)O(4)). The binding energies indicate that three of the four complexes are quite stable, with the most stable (NO(3)(-)).(N(2)O(4)) possessing binding energy of almost -14 kcal mol(-1). Vibrational frequencies were calculated for use in detecting the complexes by infrared and Raman spectroscopy. An ATR-FTIR experiment showed features at 1632 and 1602 cm(-1) that are attributed to NO(2) complexed to NO(3)(-) and HNO(3), respectively. The electronic states of (HNO(3)).(N(2)O(4)) and (NO(3)(-)).(N(2)O(4)) were investigated using an excited state method and it was determined that both complexes possess one low-lying excited state that is accessible through absorption of visible radiation. Evidence for the existence of (NO(3)(-)).(N(2)O(4)) was obtained from UV/vis absorption spectra of N(2)O(4) in concentrated HNO(3), which show a band at 320 nm that is blue shifted by 20 nm relative to what is observed for N(2)O(4) dissolved in organic solvents. Finally, hydrogen transfer reactions within the (HNO(3)).(NO(2)) and (HNO(3)).(N(2)O(4)) complexes leading to the formation of HONO, were investigated. In both systems the calculated potential profiles rule out a thermal mechanism, but indicate the reaction could take place following the absorption of visible radiation. We propose that these complexes are potentially important in the thermal and photochemical production of HONO observed in previous laboratory and field studies.     

Synthesis, photophysical and electrochemical properties of a mixed bipyridyl-phenanthrolyl ligand Ru(II) heteroleptic complex having trans-2-methyl-2-butenoic acid functionalities

In this work, two ligands: 4-(trans-2-Methyl-2-butenoic acid)-2,2'-bipyridine) (L(1)) and 5-(trans-2-methyl-2-butenoic acid)-1,10-phenanthroline (L(2)), with the corresponding mixed-ligand heteroleptic Ru(II) complex were synthesized and characterized by FT-IR, 1H-, 13C-NMR spectroscopy and elemental analysis. The influence of the mixed functionalized polypyridyl ruthenium(II) complex on the photophysical and electrochemical properties were investigated and compared to individual single-ligand homoleptic complexes. Interestingly, the mixed-ligand complex formulated as [RuL(1)L(2)(NCS)(2)] exhibits broad and intense metal-to-ligand charge transfer (MLCT) absorption with a high molar extinction coefficient (λ(max) = 514 nm, ε = 69,700 M(-1) cm(-1)), better than those of individual single-ligand complexes, [Ru(L(1))(2)(NCS)(2)] and [Ru(L(2))(2)(NCS)(2)], and a strong photoluminescence intensity ratio in the red region at λ(em) = 686 nm. The electrochemical properties of the complex indicated that the redox processes are ligand-based.     

Cationic germanium fluorides: a theoretical investigation on the structure, stability, and thermochemistry of GeFn/GeFn+ (n = 1-3)

The structure, harmonic frequencies, enthalpies of formation, and dissociation energies of the GeF(n)(+) cations (n = 1-3) and of their neutral counterparts GeF(n) have been investigated at the MP2 and CCSD(T) levels of theory and discussed in connection with previous experimental and theoretical data. The CCSD(T,full)/cc-pVTZ-optimized geometries and MP2(full)/6-311G(d) harmonic frequencies are 1.744 A and 668.0 cm(-1) for GeF((2)Pi), 1.670 A and 798.6 cm(-1) for GeF(+)((1)Sigma(+)), 1.731 A/97.4 degrees and 267.0 (a(1))/673.1 (b(2))/690.6 (a(1)) cm(-1) for GeF(2)(C(2)(v),(1)A(1)), 1.666 A/116.9 degrees and 202.3 (a(1))/769.6 (a(1))/834.6 (b(2)) cm(-1) for GeF(2)(+)(C(2)(v),(2)A(1)), 1.706 A/112.2 degrees and 214.4 (e)/273.1 (a(1))/699.6 (a(1))/734.1 (e) cm(-1) for GeF(3)(C(3)(v),(2)A(1)), and 1.644 A and 211.4 (e')/229.9 (a(2)' ')/757.4 (a(1)')/879.3 (e') cm(-1) for GeF(3)(+)(D(3)(h),(1)A(1)). These calculated values are in excellent agreement with the experimental data reported for GeF, GeF(+), and GeF(2), and should be therefore of good predictive value for the still unexplored GeF(2)(+), GeF(3), and GeF(3)(+). The comparison of the CCSD(T,full)/cc-pVTZ enthalpies of formation at 298.15 K, -11.6 (GeF), -125.9 (GeF(2)), -180.4 (GeF(3)), 158.4 (GeF(+)), 134.1 (GeF(2)(+)), and 44.8 (GeF(3)(+)) kcal mol(-1), with the available experimental data, especially for the cations, shows discrepancies which suggest the need for novel and more refined measurements. On the other hand, the computed adiabatic ionization potentials of GeF, 7.3 eV, GeF(2), 11.2 eV, and GeF(3), 9.7 eV, are in good agreement with the available experimental estimates.     

Selective recognition of cyanide anion via formation of multipoint NH and phenyl CH hydrogen bonding with acyclic ruthenium bipyridine imidazole receptors in water

Five imidazole-based anion receptors A-E are designed for cyanide anion recognition via hydrogen bonding interaction in water. Only receptors A [Ru(bpy)(2)(mpipH)](ClO(4))(2) (bpy is bipyridine and mpipH is 2-(4-methylphenyl)-imidazo[4,5-f]-1,10-phenanthroline) and E [Ru(2)(bpy)(4)(mbpibH(2))](ClO(4))(4) (mbpibH(2) is 1,3-bis([1,10]-phenanthroline-[5,6-d]imidazol-2-yl)benzene) selectively recognize CN(-) from OAc(-), F(-), Cl(-), Br(-), I(-), NO(3)(-), HSO(4)(-), ClO(4)(-), H(2)PO(4)(-), HCO(3)(-), N(3)(-), and SCN(-) anions in water (without organic solvent) at physiological conditions via formation of multiple hydrogen bonding interaction with binding constants of K(A(H2O)) = 345 ± 21 and K(E(H2O)) = 878 ± 41, respectively. The detection limits of A and E toward CN(-) in water are 100 and 5 μM, respectively. Receptor E has an appropriate pK(a2)* value (8.75) of N-H proton and a C-shape cavity structure with three-point hydrogen bonding, consisting of two NH and one cooperative phenyl CH hydrogen bonds. Appropriate acidity of N-H proton and multipoint hydrogen bonding are both important in enhancing the selectivity and sensitivity toward CN(-) in water. The phenyl CH···CN(-) hydrogen bonding interaction is observed by the HMBC NMR technique for the first time, which provides an efficient approach to directly probe the binding site of the receptor toward CN(-). Moreover, CN(-) induced emission lifetime change of the receptor has been exploited in water for the first time. The energy-optimized structure of E-CN adduct is also proposed on the basis of theoretical calculations.     

Studies of iron(II) and iron(III) complexes with fac-N2O, cis-N2O2 and N2O3 donor ligands: models for the 2-His 1-carboxylate motif of non-heme iron monooxygenases

Enzymes in the oxygen-activating class of mononuclear non-heme iron oxygenases (MNOs) contain a highly conserved iron center facially ligated by two histidine nitrogen atoms and one carboxylate oxygen atom that leave one face of the metal center (three binding sites) open for coordination to cofactor, substrate, and/or dioxygen. A comparative family of [Fe(II/III)(N(2)O(n))(L)(4-n))](±x), n = 1-3, L = solvent or Cl(-), model complexes, based on a ligand series that supports a facially ligated N,N,O core that is then modified to contain either one or two additional carboxylate chelate arms, has been structurally and spectroscopically characterized. EPR studies demonstrate that the high-spin d(5) Fe(III)g = 4.3 signal becomes more symmetrical as the number of carboxylate ligands decreases across the series Fe(N(2)O(3)), Fe(N(2)O(2)), and Fe(N(2)O(1)), reflecting an increase in the E/D strain of these complexes as the number of exchangeable/solvent coordination sites increases, paralleling the enhanced distribution of electronic structures that contribute to the spectral line shape. The observed systematic variations in the Fe(II)-Fe(III) oxidation-reduction potentials illustrate the fundamental influence of differential carboxylate ligation. The trend towards lower reduction potential for the iron center across the [Fe(III)(N(2)O(1))Cl(3)](-), [Fe(III)(N(2)O(2))Cl(2)](-) and [Fe(III)(N(2)O(3))Cl](-) series is consistent with replacement of the chloride anions with the more strongly donating anionic O-donor carboxylate ligands that are expected to stabilize the oxidized ferric state. This electrochemical trend parallels the observed dioxygen sensitivity of the three ferrous complexes (Fe(II)(N(2)O(1)) < Fe(II)(N(2)O(2)) < Fe(II)(N(2)O(3))), which form μ-oxo bridged ferric species upon exposure to air or oxygen atom donor (OAD) molecules. The observed oxygen sensitivity is particularly interesting and discussed in the context of α-ketoglutarate-dependent MNO enzyme mechanisms.     

The ammine, thiosulfato, and mixed ammine/thiosulfato complexes of silver(I) and gold(I)

The M(I)-NH(3), M(I)-S(2)O(3)(2)(-), and M(I)-S(2)O(3)(2)(-)-NH(3) systems (M = Ag, Au) were studied at 25 degrees C and at I = 0.1 M (NaClO(4)) using a variety of analytical techniques. For the Ag(I)-NH(3)-S(2)O(3)(2)(-) system, AgS(2)O(3)NH(3)(-) was detected with formation constant log beta(111) (for the reaction Ag(+) + S(2)O(3)(2)(-) + NH(3) <--> AgS(2)O(3)NH(3)(-)) of 11.2, 10.4, and 10.8 on the basis of silver potentiometry, UV-vis spectrophotometry, and hydrodynamic voltammetry, respectively. Also, the values of log beta(101)(AgNH(3)(+)), log beta(102)(Ag(NH(3))(2)(+)), log beta(110)(AgS(2)O(3)(-)), and log beta(120)(Ag(S(2)O(3))(2)(3)(-)), obtained from silver potentiometry, were 3.59, 7.0, 8.97, 13.1, respectively. In the case of the ammine complexes, the log beta(101)(AgNH(3)(+)) and log beta(102)(Ag(NH(3))(2)(+)) values were found to be 3.5 and 7.1, respectively, from the UV-vis spectrophotometric experiments. The mixed species AuS(2)O(3)NH(3)(-) was detected in UV-vis spectrophotometric, hydrodynamic voltammetric, and potentiometric experiments with the stepwise formation constants (log K(111)) of -4.0, -3.5, -3.8, respectively, for the reaction Au(S(2)O(3))(2)(3)(-) + NH(3) <--> AuS(2)O(3)NH(3)(-) + S(2)O(3)(2)(-). At higher [NH(3)]/[S(2)O(3)(2)(-)] ratios (>10(5)), the formation of Au(NH(3))(2)(+) was also detected in spectrophotometric and potentiometric experiments with stepwise formation constants (log K(102)) of -5.4 and -5.3, respectively, according to the reaction AuS(2)O(3)NH(3)(-) + NH(3) <--> Au(NH(3))(2)(+) + S(2)O(3)(2)(-).     

Equilibrium thermodynamic studies in water: reactions of dihydrogen with rhodium(III) porphyrins relevant to Rh-Rh, Rh-H, and Rh-OH bond energetics

Aqueous solutions of rhodium(III) tetra p-sulfonatophenyl porphyrin ((TSPP)Rh(III)) complexes react with dihydrogen to produce equilibrium distributions between six rhodium species including rhodium hydride, rhodium(I), and rhodium(II) dimer complexes. Equilibrium thermodynamic studies (298 K) for this system establish the quantitative relationships that define the distribution of species in aqueous solution as a function of the dihydrogen and hydrogen ion concentrations through direct measurement of five equilibrium constants along with dissociation energies of D(2)O and dihydrogen in water. The hydride complex ([(TSPP)Rh-D(D(2)O)](-4)) is a weak acid (K(a)(298 K) = (8.0 +/- 0.5) x 10(-8)). Equilibrium constants and free energy changes for a series of reactions that could not be directly determined including homolysis reactions of the Rh(II)-Rh(II) dimer with water (D(2)O) and dihydrogen (D(2)) are derived from the directly measured equilibria. The rhodium hydride (Rh-D)(aq) and rhodium hydroxide (Rh-OD)(aq) bond dissociation free energies for [(TSPP)Rh-D(D(2)O)](-4) and [(TSPP)Rh-OD(D(2)O)](-4) in water are nearly equal (Rh-D = 60 +/- 3 kcal mol(-1), Rh-OD = 62 +/- 3 kcal mol(-1)). Free energy changes in aqueous media are reported for reactions that substitute hydroxide (OD(-)) (-11.9 +/- 0.1 kcal mol(-1)), hydride (D(-)) (-54.9 kcal mol(-1)), and (TSPP)Rh(I): (-7.3 +/- 0.1 kcal mol(-1)) for a water in [(TSPP)Rh(III)(D(2)O)(2)](-3) and for the rhodium hydride [(TSPP)Rh-D(D(2)O)](-4) to dissociate to produce a proton (9.7 +/- 0.1 kcal mol(-1)), a hydrogen atom (approximately 60 +/- 3 kcal mol(-1)), and a hydride (D(-)) (54.9 kcal mol(-1)) in water.     

Copper(I) complex O(2)-reactivity with a N(3)S thioether ligand: a copper-dioxygen adduct including sulfur ligation, ligand oxygenation, and comparisons with all nitrogen ligand analogues

In order to contribute to an understanding of the effects of thioether sulfur ligation in copper-O(2) reactivity, the tetradentate ligands L(N3S) (2-ethylthio-N,N-bis(pyridin-2-yl)methylethanamine) and L(N3S')(2-ethylthio-N,N-bis(pyridin-2-yl)ethylethanamine) have been synthesized. Corresponding copper(I) complexes, [CuI(L(N3S))]ClO(4) (1-ClO(4)), [CuI(L(N3S))]B(C(6)F(5))(4) (1-B(C(6)F(5))(4)), and [CuI(L(N3S'))]ClO(4) (2), were generated, and their redox properties, CO binding, and O(2)-reactivity were compared to the situation with analogous compounds having all nitrogen donor ligands, [CuI(TMPA)(MeCN)](+) and [Cu(I)(PMAP)](+) (TMPA = tris(2-pyridylmethyl)amine; PMAP = bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine). X-ray structures of 1-B(C(6)F(5))(4), a dimer, and copper(II) complex [Cu(II)(L(N3S))(MeOH)](ClO(4))(2) (3) were obtained; the latter possesses axial thioether coordination. At low temperature in CH(2)Cl(2), acetone, or 2-methyltetrahydrofuran (MeTHF), 1 reacts with O(2) and generates an adduct formulated as an end-on peroxodicopper(II) complex [{Cu(II)(L(N3S))}(2)(mu-1,2-O(2)(2-))](2+) (4)){lambda(max) = 530 (epsilon approximately 9200 M(-1) cm(-1)) and 605 nm (epsilon approximately 11,800 M(-1) cm(-1))}; the number and relative intensity of LMCT UV-vis bands vary from those for [{Cu(II)(TMPA)}(2)(O(2)(2-))](2+) {lambda(max) = 524 nm (epsilon = 11,300 M(-1) cm(-1)) and 615 nm (epsilon = 5800 M(-1) cm(-1))} and are ascribed to electronic structure variation due to coordination geometry changes with the L(N3S) ligand. Resonance Raman spectroscopy confirms the end-on peroxo-formulation {nu(O-O) = 817 cm(-1) (16-18O(2) Delta = 46 cm(-1)) and nu(Cu-O) = 545 cm(-1) (16-18O(2) Delta = 26 cm(-1)); these values are lower in energy than those for [{Cu(II)(TMPA)}(2)(O(2)(2-))](2+) {nu(Cu-O) = 561 cm(-1) and nu(O-O) = 827 cm(-1)} and can be attributed to less electron density donation from the peroxide pi* orbitals to the Cu(II) ion. Complex 4 is the first copper-dioxygen adduct with thioether ligation; direct evidence comes from EXAFS spectroscopy {Cu K-edge; Cu-S = 2.4 Angstrom}. Following a [Cu(I)(L(N3S))](+)/O(2) reaction and warming, the L(N3S) thioether ligand is oxidized to the sulfoxide in a reaction modeling copper monooxygenase activity. By contrast, 2 is unreactive toward dioxygen probably due to its significantly increased Cu(II)/Cu(I) redox potential, an effect of ligand chelate ring size (in comparison to 1). Discussion of the relevance of the chemistry to copper enzyme O(2)-activation, and situations of biological stress involving methionine oxidation, is provided.     

Synthesis and spectroelectrochemical studies of mixed heteroleptic chelate complexes of ruthenium(II) with 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto) and substituted 1,10-phenanthrolines

Reaction of dichlorotris(triphenylphosphine) ruthenium(II) [RuCl(2)(PPh(3))(3)] with 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto), a (N(2)S(2)) tetradentate donor, yields a new compound [Ru(pdto)(PPh(3))Cl]Cl (1), which has been fully characterized. (1)H and (31)P NMR studies of 1 in acetonitrile at several temperatures show the substitution of both coordinated chloride and triphenylphosphine with two molecules of acetonitrile, as confirmed by the isolation of the complex [Ru(pdto)(CH(3)CN)(2)]Cl(2) (2). Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine the electrochemical behavior of compound 1. The substitution of the chloride and triphenylphosphine by acetonitrile molecules in the Ru(II) coordination sphere of compound 1 was also established by electrochemical studies. The easy substitution of this complex led us to use it as starting material to synthesize the substituted phenanthroline coordination compounds with (pdto) and ruthenium(II), [Ru(pdto)(4,7-diphenyl-1,10-phenanthroline)]Cl(2).4H(2)O (3), [Ru(pdto)(1,10-phenanthroline)]Cl(2).5H(2)O (4), [Ru(pdto)(5,6-dimethyl-1,10-phenanthroline)]Cl(2).5H(2)O (5), [Ru(pdto)(4,7-dimethyl-1,10-phenanthroline)]Cl(2).3H(2)O (6), and [Ru(pdto)(3,4,7,8-tetramethyl-1,10-phenanthroline)]Cl(2).4H(2)O (7). These compounds were fully characterized, and the crystal structure of 4 was obtained. Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine their electrochemical behavior. The electrochemical oxidation processes in these compounds are related to the oxidation of ionic chlorides, and to the reversible transformation from Ru(II) to Ru(III). On the other hand, a single reduction process is associated to the reduction of the substituted phenanthroline in the coordination compound. The E(1/2) (phen/phen(-)) and E(1/2) (Ru(II)/Ru(III)) for the compounds (3-7) were evaluated, and, as expected, the modification of the substituted 1,10-phenanthrolines in the complexes also modifies the redox potentials. Correlations of both electrochemical potentials with pK(a) of the free 1,10-phenathrolines, lambda(max) MLCT transition band, and chemical shifts of phenanthrolines in these complexes were found, possibly as a consequence of the change in the electron density of the Ru(II) and the coordinated phenanthroline.     

Evidence of competitive mechanisms during oxidation of CS(2)N(-)(3) by permanganate ion in alkaline solution

The oxidation of the 1,2,3,4-thiatriazole-5-thiolate ion, CS(2)N(-)(3), by permanganate ions in alkaline medium has been investigated over a wide range of oxidant concentrations. With a moderate excess of permanganate ion a 17-electron reaction takes place, yielding sulphate, nitrogen and carbon dioxide. With a high permanganate concentration the pseudohalide undergoes a 26-electron reaction yielding sulphate, carbon dioxide and nitrite as final products. These two different stoichiometries arise from the existence of competitive mechanisms and the ratio C(MnO(-)(4))/C(CS(2)N(-)(3)) will determine the course of the reaction.     

Formation and reactivity of the Os(IV)-azidoimido complex, PPN[Os(IV)(bpy)(Cl)(3)(N(4))

Reactions between the Os(VI)-nitrido complexes, [OsVI(L2)(Cl)3(N)] (L2 = 2,2'-bipyridine (bpy) ([1]), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 1,10-phenanthroline (phen), and 4,7-diphenyl-1,10-phenanthroline (Ph2phen)), and bis-(triphenylphosphoranylidene)ammonium azide (PPNN3) in dry CH3CN at 60 degrees C under N2 give the corresponding Os(IV)-azidoimido complexes, [OsIV(L2)(Cl)3(NN3)]- (L2 = bpy = [2]-, L2 = Me2bpy = [3]-, L2 = phen = [4]-, and L2 = Ph2phen = [5]-) as their PPN+ salts. The formulation of the N42- ligand has been substantiated by 15N-labeling, IR, and 15N NMR measurements. Hydroxylation of [2]- at Nalpha with O<--NMe3.3H2O occurs to give the Os(IV)-azidohydroxoamido complex, [OsIV(bpy)(Cl)3(N(OH)N3)] ([6]), which, when deprotonated, undergoes dinitrogen elimination to give the Os(II)-dinitrogen oxide complex, [OsII(bpy)(Cl)3(N2O)]- ([7]-). They are the first well-characterized examples of each kind of complex for Os.