The surfactant sensitized analytical reaction of cerium(IV) with some triphenylformazan derivatives

Cationic surfactant, cetylpyridinium bromide (CPB), sensitizes the colour reaction of cerium(IV) with 1,3-o-hydroxyphenyl-5-phenylformazan(I), 1-m-hydroxyphenyl-3-o-hydroxyphenyl-5-phenylformazan(II) and 1-m-carboxyphenyl-3-o-hydroxyphenyl-5-phenylformazan(III). The formation of a soluble ternary complex of stoichiometric ratio 1:1:1 (Ce(IV)-R-CPB) is responsible for the observed enhancement in the molar absorptivity and Sandell sensitivity of the formed complex, when a surfactant is present. The ternary complex exhibits absorption maxima at 596, 571 and 607 nm (epsilon=6.05 x 10(4), 6.28 x 10(4) and 8.06 x 10(4)L mol(-1)cm(-1)) using triphenylformazan derivatives I, II and III, respectively. Beer's law is obeyed between 0.15 and 2.5 microg ml(-1), whereas, optimum concentration range applying Ringbom method is in the range 0.30-2.25 microg ml(-1). Conditional formation constants in the presence and absence of CPB for Ce(IV) complexes have been calculated. The proposed method has been successfully applied to the analysis of magnesium-base cerium alloys and synthetic mixtures corresponding to various cerium alloys.     

Complexation and determination of palladium (II) ion with para-Cl-phenylazo-R-acid spectrophotometrically

The complexation of para-Cl-phenylazo-R-acid azo dye with Pd(II) has been studied spectrophotometrically. Protonation constant (pK(a)) of the ligand has been calculated and the stability conditional constants of para-Cl-phenylazo-R-acid ligand with palladium ion has been determined at a constant temperature (25.0 degrees C), where the molar ratio of this complex is 1:1 (metal:ligand) with logbeta(1)=3.75, and 1:2 with logbeta(2)=8.55. Solid complex of para-Cl-phenylazo-R-acid has been prepared and characterized on the basis of elemental analysis and FTIR spectral data. A procedure for the spectrophotometric determination of Pd(II) using para-Cl-phenylazo-R-acid as a new azo chromophore is proposed where it is rapid, sensitive and highly specific. Beer's law was obeyed in the range 0.50-10.00 ppm at pH 5.0-6.0 to form a violet-red complex (epsilon=7.7 x 10(4) l(-1) mol(-1) cm(-1) at lambda(max)=560 nm). Metal ions such as Cu(II), Cr(III), La(III), Yb(III), Y(III), and Rh(III) interfere with the complex. Ammonium salt of trimellitic acid is used to precipitate some of the interfering ions and a scheme for separation of Pd(II) from a synthetic mixture similar in composition to platinum ore or deposit was made.     

A new selective chromogenic reagent for the spectrophotometric determination of thallium(I) and (III) and its separation using flotation and the solid-phase extraction on polyurethane foam.

A new sensitive chromogenic reagent, 9,10-phenanthaquinone monoethylthiosemicarbazone (PET), has been synthesized and used in the spectrophotometric determination of Tl(III). In HNO3, H2SO4 or H3PO4 acids, PET can react immediately at room temperature with Tl(III) to form a red 2:1 complex with a maximum absorption at 516 nm. The different analytical parameters affecting the extraction and determination processes have been examined. The calibration curve was found to be linear over the range 0.2-10 microg cm(-3) with a molar absorptivity of 2.2 x 10(4) dm3 mol(-1) cm(-1). Sandell's sensitivity was found to be 0.0093 microg cm(-2). No interference from macroamounts of foreign ions was detected, except for Pd(II). However, Pd(II) does not affect the determination process, because its complex with PET has its lambda(max) at 625 nm. The proposed method has been applied to the determination of Tl(I and III) in synthetic and natural samples after separation by flotation (in oleic acid/kerosene) and solid-phase extraction (on polyurethane foam) techniques. The two methods were found to be accurate and not subject to random error, but solid-phase extraction was preferred because it is cheap, simpler and there is no contamination risk coming from flotation reagents.     

Functional mimic of dioxygen-activating centers in non-heme diiron enzymes: mechanistic implications of paramagnetic intermediates in the reactions between diiron(II) complexes and dioxygen

Two tetracarboxylate diiron(II) complexes, [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(C(5)H(5)N)(2)] (1a) and [Fe(2)(mu-O(2)CAr(Tol))(4)(4-(t)BuC(5)H(4)N)(2)] (2a), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate, react with O(2) in CH(2)Cl(2) at -78 degrees C to afford dark green intermediates 1b (lambda(max) congruent with 660 nm; epsilon = 1600 M(-1) cm(-1)) and 2b (lambda(max) congruent with 670 nm; epsilon = 1700 M(-1) cm(-1)), respectively. Upon warming to room temperature, the solutions turn yellow, ultimately converting to isolable diiron(III) compounds [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (1c), 4-(t)BuC(5)H(4)N (2c)). EPR and M?ssbauer spectroscopic studies revealed the presence of equimolar amounts of valence-delocalized Fe(II)Fe(III) and valence-trapped Fe(III)Fe(IV) species as major components of solution 2b. The spectroscopic and reactivity properties of the Fe(III)Fe(IV) species are similar to those of the intermediate X in the RNR-R2 catalytic cycle. EPR kinetic studies revealed that the processes leading to the formation of these two distinctive paramagnetic components are coupled to one another. A mechanism for this reaction is proposed and compared with those of other synthetic and biological systems, in which electron transfer occurs from a low-valent starting material to putative high-valent dioxygen adduct(s).     

Determination of tin (IV) in alloys and in canned food by visible spectrophotometric technique using pyrimidine azo compounds in presence of mixed surfactants

The complex of tin (IV) with 5-(4'-nitro-2',6'-dichlorophenylazo) (I) and 5-(4'-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (II) in the presence of nonyl phenoxy polyethoxyethanol (NPE) and cetyltrimethylammonium bromide (CTAB) has a sensitive absorption band with lambda max 517 and 488 nm, respectively. Under the optimal conditions, Beer-Lambert law is obeyed over the range 0.05-1.50 and 0.05-1.30 micrograms ml-1 Sn(IV) with molar absorptivity being 9.50 x 10(4) and 1.05 x 10(5) L mol-1 using ligand I and II, respectively. As compared with the visible methods which uses bromopyrogallol red (BPR) as the chromogenic reagent (lambda max = 550 nm) and that using phenylfluorone (lambda max = 360 nm), our method is highly sensitive and selective because the complexes have a high and sharp absorption band. In addition, the present method is simple and rapid, no heating or standing time is needed. By means of the mixed surfactants, the precipitation caused by the ion association of cetyltrimethyl-ammonium cation and I3- anion is avoided if iodide is used for separating micro amounts of tin(IV) from a sample matrix. An application of the proposed method to the determination of tin(IV) in a variety of alloys and in a canned food was made with satisfactory results.     

Pyridine-2-aldoxime and 6-methylpyridine-2-aldoxime as gravimetric reagents for estimation of palladium(II) and uranium(VI)

Pyridine-2-aldoiumc (I) has been found to be a sensitive reagent for the gravimetric determination of palladium(II). From chloride medium, precipitation is complete at pH 3.0-11.0, and in solution containing 1NHNO(3) to pH6.0. The compositions of the precipitates (dried at 130 degrees ) correspond to PdL(2), and PdL(2). HNO(3) (HL representing the reagent) respectively. Pd(II) can be estimated gravimetncally in presence of acetate, oxalate, tartrate, phosphate, fluoride borate, perchlorate, Cu(II), Cd, Co(II), Fe(II), Ni, Zn, Pb, Bi, Sb(III), Pt(IV), Ir(IV), Ru(III), Rh(III); Os(IV) in quantities more than twice that of Pd(II), and Ag(I), Au(III) and Fe(II) even m traces cause serious interference. The yellow uranium(VI) complex with (I) is precipitated quantitatively over the pH range 3.5-10.5 and, after washing and drying corresponds to the composition (c(6)h(5)n(2)o)(2)uo(2), The uranium(VI) complex with 6-methylpyridine-2-aldoxime (II) is precipitated quantitatively over the pH range 3.0-10.5, and after washing and drying at 120-130 degrees corresponds to UO(2),(C(7),H(7),N(2)O)(2). Both (I) and (II) are suitable for the estimation of 1-50 mg of uranium(VI) in the presence of up to 10-fold quantities ofTh(IV), La(III) and Ce(III) even when present together. Ce(IV) in quantities more than three times that of U must be reduced to Ce(III). Tartrate, citrate, phosphate, Ti(IV) and Zr interfere, but acetate, oxalate, and borate do not.     

Reductions by titanium(II) as catalyzed by titanium(IV)

The cobalt(III) complexes, [(NH3)5CoBr]2+ and [(NH3)5CoI]2+ are reduced by Ti(II) solutions containing Ti(IV), generating nearly linear (zero-order) profiles that become curved only during the last few percent of reaction. Other Co(III)-Ti(II) systems exhibit the usual exponential traces with rates proportional to [Co(III)]. Observed kinetics of the biphasic catalyzed Ti(II)-Co(III)Br and Ti(II)-Co(III)I reactions support the reaction sequence: [Ti(II)(H20)n]2+ + [Ti(IV)F5]- (k1)<==>(k -1) [Ti(II)(H2O)(n-1)]2+ + [(H2O)Ti(IV)F5]-, [Ti(II)(H2O)(n-1)]2+ + Co(III) (k2)--> Ti(III) + Co(II) with rates determined mainly by the slow Ti(IV)-Ti(II) ligand exchange (k1 = 9 x 10(-3) M(-1) s(-1) at 22 degrees C). Computer simulations of the catalyzed Ti(II)-Co(III) reaction in perchlorate-triflate media yield relative rates for reduction by the proposed active [Ti(II)(H2O)(n-1)]2+ intermediate; k(Br)/k(I) = 8.     

Separation and determination of trace amounts of beryllium(II), aluminium(III) and chromium(III) with chromotrope 2C chelates by RP-HPLC

A reversed-phase high-performance liquid chromatographic separation and determination of beryllium(II), aluminium(III) and chromium(III) with chromotrope 2C chelates on a C18-bonded stationary phase is reported. Methanol-water (45:55 v/v) containing 6 x 10(-3)M tetra-n-butylammonium bromide (TBAB) and 2 x 10(-2)M acetate buffer solution (pH 6.0) as mobile phase and with spectrophotometric detection at 530 nm was applied. The method has high sensitivity, the detection limits being 0.2 ppb for beryllium(I), 1 ppb for aluminium(III) and 2 ppb for chromium(III). Under the optimum conditions, most other metal ions did not interfere, e.g. up to 2 mg of Hg(II), Sn(II, IV), Pb(II), Bi(III), Ag(I), Zn(II), Cd(II), Cu(II), 1.5 mg of Fe(II), Co(II), Ni(II), 1.2 mg of Ca(II), Mg(II), Sr(II), Ba(II), 1 mg of Ga(III), In(III), 0.5 mg of Fe(III), 1 mg of Ga(III), In(III), 0.5 mg of Fe(III), 0.4 mg of Th(IV), Zr(IV). The method can be applied to the simultaneous determination of trace amounts of beryllium(II), aluminium(III) and chromium(III), in water, rice, flour and human hair samples.     

Fe3(CO)12与P(NEt2)2Cl的反应--两核和三核铁羰基簇合衍生物的合成和晶体结构

Fe_3(CO)_(12)与配位基前体P(NEt_2)_2Cl反应,给出4个新的两核和三核铁羰基簇合衍生物:Fe_2(CO)_6(μ-Cl)[μ-P(NEt_2)_2](Ⅰ),Fe_2(CO)_6[μ-P(NEt_2)_2]_2(Ⅱ),Fe_3(CO)_9(μ-CO)(μ_3-PNEt_2)(Ⅲ)和Fe_3(CO)_9(μ_3-PNEt_2)[P(NEt_2)_3](Ⅳ)。在反应期间,配前体分子中的P-Cl和P-N键劈开,形成的分子片Cl、PNEt_2、P(NEt_2)_2和P(NEt_2)_3作为配体与铁羰合物重新组建成上述簇合物。利用X射线衍射法测定了它们的晶体结构。Ⅰ属三斜晶系,P1空间群,晶胞参数a=0.8745(6)nm,b=0.9601(7)nm,c=1.3996(10)nm,α=74.131(11)°,β=79.480(12)°,γ=69.727(12)°,V=1.0553(13)nm~3,D_c=1.543g·cm~(-3),Z=2,R=0.0443,wR=0.0831。Ⅱ属正交晶系,Pbcn空间群,晶胞参数a=1.0153(3)nm,b=1.7543(5)nm,c=1.6860(5)nm,V=3.0031(15)nm~3,D_c=1.394g·cm~(-3),Z=4,R=0.0519,wR=0.1035。Ⅲ属单斜晶系,P2_1/c空间群,晶胞参数a=1.0280(5)nm,b=1.2113(5)nm,c=1.9192(7)nm,β=93.560(7)°,V=2.1366(16)nm~3,D_c=1.712g·cm~(-3),Z=4。Ⅳ属单斜晶系,Cc空间群,晶胞参数a=1.5875(7)nm,b=1.0359(5)nm,C=2.1919(9)nm,β=101.266(8)°,V=3.535(3)nm~3,Dc=1.443g·cm~(-3),Z=4。Ⅰ和Ⅱ为两核铁簇,其簇骨架Fe_2PCl和Fe_2P_2呈蝶状。Ⅲ和Ⅳ     

High-valent nonheme iron. Two distinct iron(IV) species derived from a common iron(II) precursor

The reaction of [Fe(II)(beta-BPMCN)(OTf)2] (1, BPMCN = N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane) with tBuOOH at low-temperature yields alkylperoxoiron(III) intermediates 2 in CH2Cl2 and 2-NCMe in CH3CN. At -45 degrees C and above, 2-NCMe converts to a pale green species 3 (lambda(max) = 753 nm, epsilon = 280 M(-1) cm(-1)) in 90% yield, identified as [Fe(IV)(O)(BPMCN)(NCCH3)]2+ by comparison to other nonheme [Fe(IV)(O)(L)]2+ complexes. Below -55 degrees C in CH2Cl2, 2 decays instead to form deep turquoise 4 (lambda(max) = 656, 845 nm; epsilon = 4000, 3600 M(-1) cm(-1)), formulated to be an unprecedented alkylperoxoiron(IV) complex [Fe(IV)(BPMCN)(OH)(OOtBu)]2+ on the basis of M?ssbauer, EXAFS, resonance Raman, NMR, and mass spectral evidence. The reactivity of 1 with tBuOOH in the two solvents reveals an unexpectedly rich iron(IV) chemistry that can be supported by the BPMCN ligand.     

Reactions of halofluorocarbons with group 6 complexes M(C(5)H(5))(2)L (M = Mo, W; L = C(2)H(4), CO). Fluoroalkylation at molybdenum and tungsten, and at cyclopentadienyl or ethylene ligands.

The molybdenum(II) and tungsten(II) complexes [MCp(2)L] (Cp = eta(5)-cyclopentadienyl; L = C(2)H(4), CO) react with perfluoroalkyl iodides to give a variety of products. The Mo(II) complex [MoCp(2)(C(2)H(4))] reacts with perfluoro-n-butyl iodide or perfluorobenzyl iodide with loss of ethylene to give the first examples of fluoroalkyl complexes of Mo(IV), MoCp(2)(CF(2)CF(2)CF(2)CF(3))I (8) and MoCp(2)(CF(2)C(6)F(5))I (9), one of which (8) has been crystallographically characterized. In contrast, the CO analogue [MoCp(2)(CO)] reacts with perfluorobenzyl iodide without loss of CO to give the crystallographically characterized salt, [MoCp(2)(CF(2)C(6)F(5))(CO)](+)I(-) (10), and the W(II) ethylene precursor [WCp(2)(C(2)H(4))] reacts with perfluorobenzyl iodide without loss of ethylene to afford the salt [WCp(2)(CF(2)C(6)F(5))(C(2)H(4))](+)I(-) (11). These observations demonstrate that the metal-carbon bond is formed first. In further contrast the tungsten precursor [WCp(2)(C(2)H(4))] reacts with perfluoro-n-butyl iodide, perfluoro-iso-propyl iodide, and pentafluorophenyl iodide to give fluoroalkyl- and fluorophenyl-substituted cyclopentadienyl complexes WCp(eta(5)-C(5)H(4)R(F))(H)I (12, R(F) = CF(2)CF(2)CF(2)CF(3); 15, R(F) = CF(CF(3))(2); 16, R(F) = C(6)F(5)); the Mo analogue MoCp(eta(5)-C(5)H(4)R(F))(H)I (14, R(F) = CF(CF(3))(2)) is obtained in similar fashion. The tungsten(IV) hydrido compounds react with iodoform to afford the corresponding diiodides WCp(eta(5)-C(5)H(4)R(F))I(2) (13, R(F) = CF(2)CF(2)CF(2)CF(3); 18, R(F) = CF(CF(3))(2); 19, R(F) = C(6)F(5)), two of which (13 and 19) have been crystallographically characterized. The carbonyl precursors [MCp(2)(CO)] each react with perfluoro-iso-propyl iodide without loss of CO, to afford the exo-fluoroalkylated cyclopentadiene M(II) complexes MCp(eta(4)-C(5)H(5)R(F))(CO)I (21, M = Mo; 22, M = W); the exo-stereochemistry for the fluoroalkyl group is confirmed by an X-ray structural study of 22. The ethylene analogues [MCp(2)(C(2)H(4))] react with perfluoro-tert-butyl iodide to yield the products MCp(2)[(CH(2)CH(2)C(CF(3))(3)]I (25, M = Mo; 26, M = W) resulting from fluoroalkylation at the ethylene ligand. Attempts to provide positive evidence for fluoroalkyl radicals as intermediates in reactions of primary and benzylic substrates were unsuccessful, but trapping experiments with CH(3)OD (to give R(F)D, not R(F)H) indicate that fluoroalkyl anions are the intermediates responsible for ring and ethylene fluoroalkylation in the reactions of secondary and tertiary fluoroalkyl substrates.     

Non-extraction batchwise and FIA determination of cationic and nonionic surfactants using Cu(II)-chromazurol S-surfactant complexes

Batchwise and FIA determinations have been developed for cationic and nonionic surfactants, based on the formation of ternary Cu(II)-chromazurol S-surfactant compounds. Optimum reaction conditions have been found (pH 8.0, lambda=590 and 630 nm, respectively). For the batchwise measurement, the molar absorption coefficient values epsilon(590)=5.1-5.7x10(4) l mol(-1) cm(-1) for cationic surfactants, epsilon(630)=0.7-1.5x10(4) l mol(-1) cm(-1) for nonionic surfactants. A factorial design has been carried out to determine the optimum flow conditions. Calibration curves were constructed and statistically evaluated for both the batchwise and FIA determination. For example, the linear concentration ranges for batch determination of the cationic surfactant cetyltrimethylammonium bromide and nonionic surfactant Marlophen NP 10 are 0-15 mug ml(-1) (R=0.9996, R.S.D.=6.62-0.64%) and 13-53 mug ml(-1) (R=0.9993, R.S.D.=4.48-1.40%), respectively; the respective detection limits are 0.02 and 4.0 mug ml(-1). For FIA determination of the same surfactants, the linear concentration ranges are 0-13 mug ml(-1) (R=0.9995, R.S.D.=4.44-0.49%) and 66-397 mug ml(-1) (R=0.9994, R.S.D.=8.92-1.12%), respectively, detection limits are 0.08 and 38 mug ml(-1), respectively.     

Synthesis and reactivity of bis(imido) uranium(VI) cyclopentadienyl complexes

The bis(imido) uranium(VI)-C(5)H(5) and -C(5)Me(5) complexes (C(5)H(5))(2)U(N(t)Bu)(2), (C(5)Me(5))(2)U(N(t)Bu)(2), (C(5)H(5))U(N(t)Bu)(2)(I)(dmpe), and (C(5)H(5))(2)U(N(t)Bu)(2)(dmpe) can be synthesized from reactions between U(N(t)Bu)(2)(I)(2)(L)(x) (L=THF, x=2; L=dmpe, x=1) and Na(C(5)R(5)) (R=H, Me); these complexes represent the first structurally characterized C(5)H(5)-compounds of uranium(VI) and they further highlight the differences between UO(2)(2+) and the bis(imido) fragment.     

Palladium(II) and platinum(II) complexes with tridentate iminophosphine ligands; synthesis and structural studies

The previously synthesised Schiff-base ligands 2-(2-Ph(2)PC(6)H(4)N[double bond, length as m-dash]CH)-R'-C(6)H(3)OH (R'= 3-OCH(3), HL(1); 5-OCH(3), HL(2); 5-Br, HL(3); 5-Cl, HL(4)) were prepared by a faster, more efficient route involving a microwave assisted co-condensation of 2-(diphenylphosphino)aniline with the appropriate substituted salicylaldehyde. HL(1-4) react directly with M(II)Cl(2)(M = Pd, Pt) or Pt(II)I(2)(cod) affording neutral square-planar complexes of general formula [M(II)Cl(eta(3)-L(1-4))](M = Pd, Pt, 1-8) and [Pt(II)I(eta(3)-L(1-4))](M = Pd, Pt, 9-12). Reaction of complexes 1-4 with the triarylphosphines PR(3)(R = Ph, p-tolyl) gave the novel ionic complexes [Pd(II)(PR(3))(eta(3)-L(1-4))]ClO(4)(13-20). Substituted platinum complexes of the type [Pt(II)(PR(3))(eta(3)-L(1-4))]ClO(4)(R = P(CH(2)CH(2)CN)(3)21-24) and [Pt(II)(P(p-tolyl)(3))(eta(3)-L(3,4))]ClO(4)( 25 and 26 ) were synthesised from the appropriate [Pt(II)Cl(eta(3)-L(1-4))] complex (5-8) and PR(3). The complexes are characterised by microanalytical and spectroscopic techniques. The crystal structures of 3, 6, 10, 15, 20 and 26 were determined and revealed the metal to be in a square-planar four-coordinate environment containing a planar tridentate ligand with an O,N,P donor set together with one further atom which is trans to the central nitrogen atom.     

Probing the ruthenium-cumulene bonding interaction: synthesis and spectroscopic studies of vinylidene- and allenylidene-ruthenium complexes supported by tetradentate macrocyclic tertiary amine and comparisons with diphosphine analogues of ruthenium and osmium

The synthesis and spectroscopic properties of trans-[Cl(16-TMC)Ru[double bond]C[double bond]CHR]PF(6) (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, R = C(6)H(4)X-4, X = H (1), Cl (2), Me (3), OMe (4); R = CHPh(2) (5)), trans-[Cl(16-TMC)Ru[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (X = H (6), Cl (7), Me (8), OMe (9)), and trans-[Cl(dppm)(2)M[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (M = Ru, X = H (10), Cl (11), Me (12); M = Os, X = H (13), Cl (14), Me (15)) are described. The crystal structures of 1, 5, 6, and 8 show that the Ru-C(alpha) and C(alpha)-C(beta) distances of the allenylidene complexes fall between those of the vinylidene and acetylide relatives. Two reversible redox couples are observed by cyclic voltammetry for 6-9, with E(1/2) values ranging from -1.19 to -1.42 and 0.49 to 0.70 V vs Cp(2)Fe(+/0), and they are both 0.2-0.3 and 0.1-0.2 V more reducing than those for 10-12 and 13-15, respectively. The UV-vis spectra of the vinylidene complexes 1-4 are dominated by intense high-energy bands at lambda(max) < or = 310 nm (epsilon(max) > or = 10(4) dm(3) mol(-1) cm(-1)), while weak absorptions at lambda(max) > or = 400 nm (epsilon(max) < or = 10(2) dm(3) mol(-1) cm(-1)) are tentatively assigned to d-d transitions. The resonance Raman spectrum of 5 contains a nominal nu(C[double bond]C) stretch mode of the vinylidene ligand at 1629 cm(-1). The electronic absorption spectra of the allenylidene complexes 6-9 exhibit an intense absorption at lambda(max) = 479-513 nm (epsilon(max) = (2-3) x 10(4) dm(3) mol(-1) cm(-1)). Similar electronic absorption bands have been found for 10-12, but the lowest energy dipole-allowed transition is blue-shifted by 1530-1830 cm(-1) for the Os analogues 13-15. Ab initio calculations have been performed on the ground state of trans-[Cl(NH(3))(4)Ru[double bond]C[double bond]C[double bond]CPh(2)](+) at the MP2 level, and imply that the HOMO is not localized purely on the metal center or allenylidene ligand. The absorption band of 6 at lambda(max) = 479 nm has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal nu(C[double bond]C[double bond]C) stretch mode accounts for ca. 50% of the total vibrational reorganization energy, indicating that this absorption band is strongly coupled to the allenylidene moiety. The excited-state reorganization of the allenylidene ligand is accompanied by rearrangement of the Ru[double bond]C and Ru[bond]N (of 16-TMC) fragments, which supports the existence of bonding interaction between the metal and C[double bond]C[double bond]C unit in the electronic excited state.     

Spectroscopic studies and structures of trans-ruthenium(II) and ruthenium(III) bis(cyanide) complexes supported by a tetradentate macrocyclic tertiary amine ligand

trans-[Ru(16-TMC)(C[triple bond]N)2] (1; 16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane) was prepared by the reaction of trans-[Ru(16-TMC)Cl2]Cl with KCN in the presence of zinc powder. The oxidation of 1 with bromine gave trans-[Ru(16-TMC)(CN)2]+ isolated as PF6 salt (2.PF6). The Ru-C/C-N distances are 2.061(4)/1.130(5) and 2.069(5)/1.140(7) A for 1 and 2, respectively. Both complexes show a Ru(III/II) couple at 0.10 V versus FeCp2+/0. The UV-vis absorption spectrum of 1 is dominated by an intense high-energy absorption at lambda(max) = 230 nm, which is mainly originated from dpi(RuII) --> pi*(N[triple bond]C-Ru-C[triple bond]N) charge-transfer transition. Complex 2 shows intense absorption bands at lambda(max) pi*(N[triple bond]C-Ru-C[triple bond]N) and sigma(-CN) --> d(RuIII) charge-transfer transition, respectively. Density functional theory and time-dependent density-functional theory calculations have been performed on trans-[(NH3)4Ru(C[triple bond]N)2] (1') and trans-[(NH3)4Ru(C[triple bond]N)2]+ (2') to examine the Ru-cyanide interaction and the nature of associated electronic transition(s). The 230 nm band of 1 has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal nuC[triple bond]N stretch mode accounts for ca. 66% of the total vibrational reorganization energy. A change of nominal bond order for the cyanide ligand from 3 to 2.5 is estimated upon the electronic excitation.     

4,4'-dithiodipyridine as a bridging ligand in osmium and ruthenium complexes: the electron conductor ability of the -S-S- bridge

The compounds [Ru(NH(3))(5)(dtdp)](TFMS)(3), [Os(NH(3))(5)(dtdp)](TFMS)(3), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](TFMS)(6), [(NH(3))(5)Os(dtdp)Ru(NH(3))(5)](TFMS)(3)(PF(6))(2), and [(NH(3))(5)Os(dtdp)Fe(CN)(5)] (dtdp = 4,4'-dithiodipyridine, TFMS = trifluoromethanesulfonate) have been synthesized and characterized by elemental analysis, cyclic voltammetry, electronic, vibrational, EPR, and (1)H NMR spectroscopies. Changes in the electronic and voltammetric spectra of the ion complex [Os(NH(3))(5)(dtdp)](3+) as a function of the solution pH enable us to calculate the pK(a) for the [Os(NH(3))(5)(dtdpH)](4+) and [Os(NH(3))(5)(dtdpH)](3+) acids as 3.5 and 5.5, respectively. The comparison of the above pK(a) data with that for the free ligand (pK(1) = 4.8) provides evidence for the -S-S- bridge efficiency as an electron conductor between the two pyridine rings. The symmetric complex, [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](6+), is found to exist in two geometric forms, and the most abundant form (most probably trans) has a strong conductivity through the -S-S- bridge, as is shown by EPR, which finds it to have an S = 1 spin state with a spin-spin interaction parameter of 150-200 G both in the solid sate and in frozen solution. Further the NMR of the same complex shows a large displacement of unpaired spin into the pi orbitals of the dttp ligand relative to that found in [Os(NH(3))(5)(dtdp)](3+). The comproportionation constant, K(c) = 2.0 x 10(5), for the equilibrium equation [Os(II)Os(II)] + [Os(III)Os(III)] right harpoon over left harpoon 2[Os(II)Os(III)] and the near-infrared band energy for the mixed-valence species (MMCT), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](5+) (lambda(MMCT) = 1665 nm, epsilon = 3.5 x 10(3) M(-)(1) cm(-)(1), deltanu(1/2) = 3.7 x 10(3) cm(-)(1), alpha = 0.13, and H(AB) = 7.8 x 10(2) cm(-)(1)), are quite indicative of strong electron delocalization between the two osmium centers. The electrochemical and spectroscopic data for the unsymmetrical binuclear complexes [(NH(3))(5)Os(III)(dtdp)Ru(II)(NH(3))(5)](5+) (lambda(MMCT) = 965 nm, epsilon = 2.2 x 10(2) M(-)(1) cm(-)(1), deltanu(1/2) = 3.0 x 10(3) cm(-)(1), and H(AB) = 2.2 x 10(2) cm(-)(1)) and [(NH(3))(5)Os(III)(dtdp)Fe(II)(CN)(5)] (lambda(MMCT) = 790 nm, epsilon = 7.5 x 10 M(-)(1) cm(-)(1), deltanu(1/2) = 5.4 x 10(3) cm(-)(1), and H(AB) = 2.0 x 10(2) cm(-)(1)) also suggest a considerable electron delocalization through the S-S bridge. As indicated by a comparison of K(c) and energy of the MMCT process in the iron, ruthenium, and osmium complexes, the electron delocalization between the two metal centers increases in the following order: Fe < Ru < Os.     

Extractive-spectrophotometric determination of molybdenum with 4-unsubstituted-5-pyrazolones

A fairly sensitive and selective method for rapid determination of tracer amounts of molybdenum(V) as mixed-ligand complexes with thiocyanate and 4-unsubstituted-5-pyrazolones is described. The red complexes are extractable into chloroform from 1-5M hydrochloric or perchloric acid or 1-3M sulphuric arid media. The molar absorptivities are in the range 1.72-2.15 x 10(4)l.mole(-1).cm(-1) at 455 nm (lambda(max)). The method has been applied to the estimation of molybdenum in various synthetic and alloy-steel samples. In presence of excess of the reagent, Cu(II), Co(II), Mn(II), Fe(II), Fe(III), Al(III), Cr(III), Cr(VI), Ti(III), Ti(IV), Zr(IV), Hf(IV), V(III), V(IV), V(V), Nb(V), Ta(V), W(VI) and U(VI) do not interfere.     

Determination of platinum(IV) by UV spectrophotometry

A simple, rapid and sensitive spectrophotometric procedure for the determination of platinum has been elaborated. Pt traces were determined in the form of the PtCl(6)(2-) complex in hydrochloric acid solution whose concentration varies from 0.01 to 2 mol L(-1) by measuring the absorbance at 260 nm. The detection limit is 4.7 x 10(-7) mol L(-1), the linearity range from 2 x 10(-6) mol L(-1) to 7 x 10(-6) mol L(-1), and the correlation coefficient is r=0.9990. No significant interferences were observed from a majority of the investigated ions, such as Zn(II), Pb(II), Mn(II), Cd(II), Co(II) and Ni(II) with the exception of Cu(II), Sb(III), Fe(III), Pd(II), Sn(II) and I(-) ions. The method was successfully applied for the determination of Pt traces in different solid samples and the recovery from inorganic materials was studied.     

Photochemical behavior of azobenzene-conjugated CoII, CoIII, and FeII bis(terpyridine) complexes

Azobenzene-conjugated mononuclear and dinuclear terpyridyl complexes of Co(II), Co(III), and Fe(II) were synthesized, and their photoisomerization behavior was investigated. Co(II) and Co(III) complexes, [tpyCo(tpy-AB)]X(n) and [(Cotpy)(2)(tpy-AB-tpy)]X(n) (tpy-AB = C(15)N(3)H(10)-C(6)H(4)-N=NC(6)H(5), tpy-AB-tpy = C(15)N(3)H(10)-C(6)H(4)-N=NC(6)H(4)-C(15)N(3)H(10), X = PF(6) or BPh(4)), exhibit trans-to-cis photoisomerization by irradiation at 366 nm, and this behavior is dependent on solvents and counterions. For the Co(II) complexes, BPh(4) salts undergo cis-to-trans isomerization in propylene carbonate by both photoirradiation with visible light (435 nm) and heat, indicating that reversible trans-cis isomerization has occurred. [Co(tpy-AB)(2)](BPh(4))(2) shows a two-step trans-to-cis isomerization process. The trans-cis isomerization behavior of Co(III) complexes was observed only in the solvents with a low donor number such as 1,2-dichloroethane. Fe(II) complexes, [tpyFe(tpy-AB)]X(n) (X = PF(6) or BPh(4)), exhibit slight trans-to-cis photoisomerization due to the energy transfer from the azobenzene moiety to Fe(tpy)(2) moieties.