Stable free-radical complexing reagents in applications of electron spin resonance to the determination of metals: Part 2. Spin-labelled iminooxime [1]

Possibilities for the determination of metals by means of the intensity of the e.s.r. signal of the chelate-fonning reagent, spin-labelled iminomonoxime — 4-oximinomethyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl, have been studied. The dissociation constant of the oxime group (pK^T_a = 9.36 ± 0.08) and the reagent partition constant in the chloroform—water system (log K_D = 0.80 ± 0.11) are reported. The reagent extracts copper, cobalt and nickel into chloroform. Copper is extracted as its CuA₂, chelate (log K_D = 0.91 ± 0.03; log K_ex = -3.35 ± 0.09; log β₂, = 15.8 ± 0.2). Several properties of the spin-labelled and conventional oximes are compared. It is confirmed that a radical-containing substituent produces a strong electron-acceptor effect. Unusual extractive and e.s.r.- spectroscopic behaviour of cobalt is indicated; an adduct of the spin-labelled chelate with atmospheric oxygen seems to be formed. Methods for the determination of cobalt and nickel based on the extraction with spin-labelled oxime into chloroform and subsequent separation of the excess of reagent on a chromatographic column are described. The detection limits are 3 × 10^-7 M for cobalt and 10^-6 M for nickel.     

Kinetische und mechanistische untersuchungen von übergansmetallkomplex-reaktionen: XXI. Einfluss von zentralmetall,trans-X-ligand und carbinsubstituent auf die MCO-dissoziation in carbin-komplexen des typs trans-X(CO)4MCR

The influence of the central metal atom, the trans-X ligand, and the carbyne substituent R on the MCO dissociation step of seventeen different carbyne complexes, trans-(CO)₄MCR (X = Cl, Br, I, SePh; M = Cr, W; R = Me, aryl, NEt₂), in 1,1,2-trichloroethane was studied by means of the substitution of one CO ligand by PPh₃. All complexes react with PPh₃ according to the first-order rate equation: — d[complex]/dt = k[complex]. The activation enthalpies ΔH³ are in the range 97–116 kJ mol⁻¹, the activation entropies ΔS³ are 34 to 72 J mol⁻¹ K⁻¹. The reaction rate, (i) is virtually independent of the electronic properties of R, (ii) decreases slightly with increasing steric requirements of R, (iii) increases strongly in the series trans-X = I, Br, Cl, SePh, and (iv) is faster for chromium complexes than for analogous tungsten compounds by a factor of ca. 30 to 50. There is no general correlation between the rate constants k and the CO force constants k(CO). The variation in the reaction rate is essentially determined by the different levels of stabilization of energy in the transition state. The thermolysis of carbyne complexes is also initiated by CO dissociation. The rate of thermolysis when [CO] = 0 is equal to the rate of CO/PPh₃ substitution; it decreases rapidly with increasing CO concentration in the solution; and when [CO] = constant it increases significantly with increasing concentration of the complex. A mechanistic scheme is proposed for the thermolysis which involves three different reaction pathways for the coordinatively unsaturated fragment X(CO)₃MCR formed by CO dissociation from trans-X(CO)₄MCR: readdition of CO, monomolecular decomposition, and reaction with trans-X(CO)₄MCR.     

Relative reactivities of heteroaromatic cations towards reduction by 1,4-dihydronicotinamides

Kinetic data are reported for the equilibration of the 1-methyl-3-nitropyridinium cation with its pseudobase (hydroxide adduct) and for the reduction of this cation by 1-benzyl-1, 4-dihydronicotinamide. The C-2 hydroxide adduct is the kinetically controlled product (pK_R+ = 11.6) when this pyridinium cation is mixed with aqueous base, however, this species rearranges to the C-4 adduct as the themodynamically more stable product (pK_R+ = 9.42). The pH-dependence of this equilibration may be analysed to give k_OH = 1600 M^-1s^-1 for hydroxide ion attack at C-4 of this cation. Reduction of this pyridinium cation by 1-benzyl-1, 4-dihydronicotinamide appears to occur exclusively at C-4 with second-order rate constant k₂ = 0.72 M^-1s^-1 and k₂ ^H/k₂^D = 2.0 in 20% CH₃CN - 80% H₂O, ionic strength 1.0, 25°C.The reactivities of pyridinium, quinolinium, isoquinolinium, acridinium and phenanthridinium cations of pK_R+ = 10.0 towards both hydroxide ion and 1-benzyl-1, 4-dihydronicotinamide are evaluated. Relative reactivities (K₂/K_OH) for these two processes are shown to be acridinium : quinolinium (C-4) : pyridinium (C-4) : quinolinium (C-2) : isoquinolinium : phenanthridinium = 1.6×10⁵ : 3400 : 80 : (4 : 1.0 : 0.7 for predominantly aqueous reaction media. These data support the hypothesis that formation of 1, 2-dihydropyridine systems upon reduction of heteroaromatic cations by 1, 4-dihydronicotinamides occurs via direct one step hydride transfer, while formation of 1,4-dihydro-pyridines in such processes occurs preferentially by a mechanistica11y more complex process involving electron transfer.     

Gleichgewichte der Protonenaddition an 1, 1-Bis-(4′, 4″-dimethylaminophenyl)-äthylen in Methanol und in Dimethylsulfoxid

The first and second proton addition equilibrium constants of 1,1-bis-(4′, 4″-dimethylaminophenyl)-ethylene ( 1 ) have been measured by the spectrophotometric method in methanol and in dimethylsulfoxide. Defined as acid dissociation constants of the mono- and diprotonated adduct they are: K₁ (CH₃OH) = 8.3 (± 0.9) · 10^?6M, K₂ (CH₃OH) = 1.22 (± 0.06) · 10^?4M, K₁ (DMSO) = 2.3 (± 0.9) · 10^?3M, K₂ (DMSO) ≥ 1M. The evaluation of the electronic and the NMR. spectra demonstrates that the equilibrium of the two monoprotonated tautomers 2 (methyl-carbenium ion) and 3 (ammonium ion) is, in methanol to about 96% on the side of the ammonium ion (tautomeric equilibrium constant K₂₃ = [3]/[2] ? 23). The tautomer 2 cannot be detected in dimethylsulfoxide. The possible causes of these solvent effects are discussed.     

Thermodynamics and kinetics of complexation of iron(III) ion by picolinic and dipicolinic acids

The complexation reactions of iron(III) with 2-pyridine carboxylic acia (picolinic acid) and 2,6-pyridine dicarboxylic acid (dipicolinic acid) in aqueous solutions have been studied by spectrophotometric and stopped flow techniques. Equilibrium constants were determined for the 1 : 1 complexes at temperatures between 25 and 80°C. The values obtained are: Picolinic Acid (HL): Fe³⁺+ H₂L⁺? FeHL³⁺+H+(K₁ = 2.8,ΔH = 2 kcal mole^?1 at 25°C, μ = 2.67 M) Dipicolinic Acid (H₂D): Fe³⁺+H₂D? FeD⁺+2H⁺(K₁K_1A= 227 M, ΔH = 3.4 kcal mole^?1 at 25°C,μ = 1.0 M). The rate constants for the formation of these complexes are also given. The results are used to evaluate the effects of these two acids upon the rate of dissolution of iron(III) from its oxides.     

The vanadium monophosphates AVOPO4: Synthesis of a second form β-KVOPO4 and structural relationships in the series

A new form of potassium vanadophosphate β-KVOPO₄ has been synthesized using hydrothermal technique which showed the role of the extra adduct, here W or WO₃. The structure of this phase, isotypic to Rb and Cs monophosphates, has been determined from a single crystal X-ray study. Structural relationships between the different monophosphates of the AVOPO₄ series with A = Li, Na, K, Rb, Cs, NH₄ are presented in which K⁺ appears as a boundary cation: with cations smaller than K⁺ the vanadium(IV) is octahedral and pyramidal with larger ones, both coordinations existing with K⁺.     

Stability constants of D(−)-ribose complexes with calcium in diluted aqueous and methanolic solutions

The study of D(?)-ribose complexing with calcium in aqueous solutions less than 1.64 × 10^?1M by potentiometric measurements with a calcium selective electrode afforded the value of K₁ = 1.70 liters × mole^?1 (SD = 1.05 × 10^?3). Numerical analysis indicated that complex species with 1:1 and 1:2 calcium to D(-)-ribose ratios are present simultaneously: k₁ = 1.13 liters × mole^?1 and K₂ = 8.47 liters × mole^?1 (SD = 0.95 × 10^?3).In methanolic medium 1.24 × 10^?2M with regard to calcium chloride both stoichiometric proportions were evidenced. A large error accompanying the stability constant K₁ = 28 kg × mole^?1 (RSD = 82%) renders unreasonable the K₂ value obtained from the product K₁ × K₂ = 96.5 kg² × mole^?2.The results are discussed with respect to the data published for more concentrated (1.27 M) aqueous solutions obtained on the basis of ₁H-NMR spectroscopic investigations.     

Ammonium (18-Crown-6)(Triphenylphosphine Oxide) Perchlorate: Synthesis and Crystal Structure

A new compound, ammonium (18-crown-6)(triphenylphosphine oxide) perchlorate (I), is synthesized, and its crystal structure is studied using X-ray diffraction analysis (space group R3m, a = 14.432 Å, c = 14.034 Å, Z = 3, direct method, full-matrix least-squares method in the anisotropic approximation, R = 0.064 for 1945 independent reflections, CAD4 automated diffractometer, λMoKα radiation). In the structure, the NH ₄ ⁺ cation resides in the 18-crown-6 macrocycle cavity and is hydrogen-bonded with three symmetrically equivalent O atoms of the 18-crown-6 molecule and with the phosphoryl O atom of the Ph₃PO molecule. The P=O H-N and Cl atoms occupy the partial position 3m. The oxygen atoms of the ClO ₄ ^? anion are disordered over the 3m position.     

The photolysis of acylphosphine oxides: III: Laser flash photolysis studies with pivaloyl compounds

Argon-saturated dilute solutions of pivaloyldiphenylphosphine oxide (PDPO), dimethylpivaloyl phosphonate (PDME) and diethylpivaloyl phosphonate (PDEE) in various solvents were irradiated with 20 ns flashes of 347 nm light. All compounds underwent α scission from excited singlet states: Φ(α) ≈ 1 (PDPO) and Φ(α) ≈ 0.3 (PDME and PDEE). The singlet lifetimes (determined by single-photon counting) are 30 ns for PDPO and 11 ± 3 ns for PDME and PDEE. In the case of PDPO, singlet deactivation occurs predominantly via α scission. In the case of the phosphonates, triplets are also formed (Φ(T) = 0.6; τ = 30 ns) as revealed from quenching with naphthalene. Dimethoxyphosphonyl and diethoxyphosphonyl radicals reacted very effectively with styrene (k_R.+St = 2 × 10⁸ M⁻¹ s⁻¹), as was indicated by the formation of the chracteristic absorption of adduct styryl radicals at 322 nm. In the case of diphenylphosphonyl radicals k_R.+St is about three times lower, which is thought to result from the rather flattened tetrahedral structure of this radical as compared with the pronounced tetrahedral structure of O=Ṗ(OR)₂ radicals. In the case of the phosphonates, the optical absorption spectra of three transients with different lifetimes were recorded which were tentatively assigned to biradicals, phosphonyl radicals and pivaloyl radicals. The extinction coefficient ϵ_{260 nm} of pivaloyl radicals is 2.8 × 10³ M⁻¹ cm⁻¹.     

Affinity capillary electrophoretic study of K+/Na+ selectivity of hexaarylbenzene-based polyaromatic receptor

Affinity capillary electrophoretic (ACE) study has proved the selectivity of hexaarylbenzene-based polyaromatic receptor (R) for K⁺ ion over Na⁺ ion. The apparent binding constants of the R complexes with K⁺ and Na⁺ ions were determined from the dependence of effective electrophoretic mobility of R on the concentration of the above alkali metal ions in the background electrolyte using a non-linear regression analysis. The apparent binding constants (K_b) of the K-R⁺ and Na–R⁺ complexes in methanolic medium were evaluated as log K_b = 3.20 ± 0.22 for the K–R⁺ complex, and log K_b??0.7 for the Na–R⁺ complex.     

Spectrophotometric determination of vanadium in petroleum crudes and derivatives

The spectrophotometric study of the complexation reaction between 5,5′methylenedisalicylhydroxamic acid and V(V) shows that two complexes are formed, the 1:1 (? = 5100 liters mol^?1 cm^?1 at 490 nm, log K_est = 5.8 ± 0.1) and the 1:2 (L:V) (? = 6250 liters mol^?1 cm^?1 at 600 nm, log K_est = 6.1 ± 0.1). A spectrophotometric method is developed for the determination of vanadium (2–9 ppm) at 2 N HCl and 495 nm, which allows its determination in petroleum crude oils with a series of advantages over the ASTM D-1548-63 method.     

Potassium halide adducts as reagent ions in infrared laser desorption/ionization fourier transform ion cyclotron resonance mass spectrometry

Potassium halide adducts of the form K₂X⁺ (X = F, CI, Br, and I) desorbed from neutral salts by high power, pulsed, infrared laser radiation are detected in abundance by Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry. FT-ICR detection of the K₂X⁺ adduct is favored at increased laser power densities (> 10⁸ W/cm²) and at trapping potentials below 3 V, independent of X. In contrast, detection of K⁺ is promoted at laser power densities below 10⁸ W/cm² or at higher trapping potentials, with a threshold for trapping that is strongly dependent on X. When laser desorption/ionization (LDI)/FT-ICR is performed on 1:1 mixtures of KX and organic molecules, ejection pulses applied continuously at the cyclotron resonance frequency of K₂X⁺ inhibit formation of the cation-attached product, [M + K]⁺. Conversely, resonance ejection of K⁺ enhances [M + K]⁺, apparently by reducing the matrix ion population trapped in the cell. In evaluating higher molecular weight adducts, only K₃F ₂ ⁺ formed in abundance by laser desorption of KF is found through double resonance experiments to contribute significantly to formation of [M + K]⁺. Finally, among the potassium halides, KI generates the highest ratio of detected K₂X⁺ to K⁺ at low trapping potentials and is therefore best suited for cation-transfer reactions in infrared LDI/FT-ICR experiments performed at power densities in the 10⁸ W/cm² range.     

Synthesis,structure and ethylene polymerization of group 4 complexes with phosphinoamide ligands

Group 4 complexes containing diphosphinoamide ligands [Ph₂PNR]₂MCl₂ (3: R = ^tBu, M = Ti; 4: R = ^tBu, M = Zr; 5: R = Ph, M = Ti; 6: R = Ph, M = Zr) were prepared by the reaction of MCl₄ (M = Ti; Zr) with the corresponding lithium phosphinoamides in ether or THF. The structure of [Ph₂PN^tBu]₂TiCl₂ (3) was determined by X‐ray crystallography. The phosphinoamides functioned as η²‐coordination ligands in the solid state and the Ti? N bond length suggests it is a simple single bond. In the presence of modified methylaluminoxane or i‐Bu₃Al/Ph₃BC(C₆F₅)₄, catalytic activity of up to 59.5 kg PE/mol cat h bar was observed. Copyright © 2005 John Wiley & Sons, Ltd.     

Phase equilibria in the systems Rb2MoO4-R2(MoO4)3-Hf(MoO4)2 (R = Al, In, Sc, Fe(III)) and the crystal structure of double molybdate RbFe(MoO4)2

The systems Rb₂MoO₄-R₂(MoO₄)₃-Hf(MoO₄)₂ have been investigated in the subsolidus region by X-ray powder diffraction, DTA, and IR spectroscopy. Triple molybdates of the composition 5: 1: 2 are formed in the systems with R = Al, In, Sc, and Fe. Molybdates of composition 5: 1: 3 and 1: 1: 1 are found in the iron(III)-containing system in addition to the 5: 1: 2 molybdate. Single crystals of the double molybdate RbFe(MoO₄)₂, which is formed in the Rb₂MoO₄-Fe₂(MoO₄)₃ system, have been grown. The structure of this double molybdate has been refined using X-ray diffraction data (X8 APEX automated diffractometer, MoK _α radiation, 373 F(hkl), R = 0.0287). The trigonal unit cell parameters are the following: a = b = 5.6655(2) Å, c = 7.5061(4) Å, V = 208.65(1) ų, Z = 1, ρ_calc = 3.670 g/cm³, space group R3m1. The structure is formed by layers of FeO₆ octahedra sharing corners with MoO₄ tetrahedra and RbO₁₂ icosahedra.     

Spectkophotometric determination of the dissociation constants of n,n'-bis(3-hydroxypropyl)dithiooxamide and n,n'-bis(2-hydroxypropyl)dithiooxamide

The dissociation constants of N,N'-bis(3-hydroxypropyl)dithiooxamide and N,N'-bis(2-hydroxypropyl)dithiooxamide were determined by a spectrophotometric method using a weighted least squares technique for the calculations. For N,N'-bis(3-hydroxypropyl) dithiooxamide a thermodynamic constant pK₁^T of 11.37 was found. At ionic strength μ = 1, pK₁ = 11.27 and pK₂ = 14.29. For N,N'-bis-(2-hydroxypropyl) dithiooxamide, these values were respectively: pK₁^T = 11.11; pK₁ = 10.99 and pK₂ = 13.75.     

Properties of the Magnesium(II) and Calcium(II) Complexes of 5‐ and 6‐Uracilmethylphosphonate (5 Umpa2– and 6 Umpa2–) in Aqueous Solution

The stability constants of the 1 : 1 complexes formed between Mg²⁺ or Ca²⁺ and 5 Umpa^2– or 6 Umpa^2– were determined by potentiometric pH titrations in aqueous solution (25 °C; I = 0.1 M, NaNO₃). Based on previously established log K^M_M(R‐PO3) versus pK^H_H(R‐PO3) straight‐line plots (M²⁺ = Mg²⁺ or Ca²⁺; R‐PO₃^2– = simple phosphate monoester or phosphonate ligands where R is a non‐interacting residue), it is shown that the Mg(5 Umpa), Ca(5 Umpa), Mg(6 Umpa) and Ca(6 Umpa) complexes have the stability expected on the basis of the basicity of the phosphonate group in 5 Umpa^2– and 6 Umpa^2–. This means, these ligands may be considered as simple analogues of nucleotides, e. g. of uridine 5′‐monophosphate. In the higher pH range deprotonation of the uracil residue in the M(5 Umpa) and M(6 Umpa) complexes occurs and this leads to the negatively charged M(5 Umpa–H)^– and M(6 Umpa–H)^– species. Based on the comparison of various acidity constants it is shown that the M(5 Umpa) complexes are especially acidic; or to say it differently, the M(5 Umpa–H)^– species are especially stable. This increased stability is attributed to the formation of a seven‐membered chelate involving next to the phosphonate group also the carbonyl oxygen atom at C4 (after deprotonation of the (N3)H site). The formation degree of this chelated isomer reaches about 45% for the Mg(5 Umpa–H)^– and Ca(5 Umpa–H)^– species. No indication for chelate formation was observed for the M(6 Umpa–H)^– complexes.     

Synthesis and crystal structure of ternary molybdate compound K<Subscript>5</Subscript>Pb<Subscript>0.5</Subscript>Hf<Subscript>1.5</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>6</Subscript>

Single crystals of triple molybdate of composition 5:1:3 K₅Pb_0.5Hf_1.5(MoO₄)₆ have been grown and their crystal structure has been solved from X-ray diffraction data (an automated diffractometer X8 APEX, MoK _α -radiation, 2173 F(hkl), R = 0.0321). Trigonal unit cell parameters are: a = b = 10.739(2) Å, c = 37.933(9) Å; V = 3789(1) ų, Z = 6, ρ_calc = 4.014 g/cm³, space group \(R\bar 3\). Three-dimensional mixed framework of the structure is formed by two types of MoO₄ tetrahedra and Pb and Hf octahedra linking via common O-vertices. Potassium atoms of three types occupy large vacancies in the framework.     

Synthesis and selective silylation of ω-hydroxy functionalized (η-alkenyl)carbene complexes of chromium(0) and tungsten(0) Part 11. The chemistry of metallacyclic alkenylcarbene complexes

Tungsten(0) carbene complexes of the type (OC)₅WC(NMeCH₂CHCHCH₂OH)R 2 (R=Me: 2a; R=Ph: 2b) were generated by aminolysis of (OC)₅WC(OMe)R with cis-NHMeCH₂CHCHCH₂OH. Like their Cr-congeners 1, complexes 2 exist at room temperature as mixtures of Z- and E-isomers with regard to the C-N bond. The metallacyclic complexes (OC)₄WC(η²-NMeCH₂CHCHCH₂OH)R (4) were obtained in good yields upon photo-decarbonylation of 2. Deprotonation/silylation of the complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)Me (M=Cr: 3a; M=W: 4a) with one equivalent of ⁿBuLi/Me₃SiCl gave (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₃ (M=Cr: 5; M=W: 6), whereas with two equivalents of ⁿBuLi/Me₃SiCl complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₂SiMe₃ (M=Cr: 7; M=W: 8) were formed. Hydrolysis of the latter yielded selectively (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)CH₂SiMe₃ (M=Cr: 9; M=W: 10). The complexes 1-10 were analyzed in solution by one- and two-dimensional NMR spectroscopy (¹H, ¹³C, ²⁹Si, ¹H/¹H COSY, ¹H/¹H NOESY, ¹³C/¹H HETCOR).     

Complexation of Osmium(IV) with 3-Methyl-2,6-Dimercapto-1-Thiopyrone-4 and Its Catalytic Application

The reaction of osmium(IV) with 3-methyl-2,6-dimercapto-1-thiopyrone-4 was studied by spectrometry, amperometry, and potentiometry. In a pH range of 2–4 M HCl (2 M H₂SO₄), insoluble osmium methyl thiopyrone dimercaptides formed with a metal-to-ligand ratio of 1 : 1, 1 : 2, 1 : 3, 1 : 4, and 1 : 6 in HCl solutions and of 1 : 1, 1 : 2, 1 : 3, and 1 : 5 in H₂SO₄ solutions. Conditional stability constants and molar absorption coefficients were determined for the products formed in the presence of excess reagent (n = 3, P = 0.95): logβ = 24.42 ± 0.02 and ε = (2.95 α 0.01) × 10⁴ for the 1 : 5 complex and logβ = 30.24 ± 0.10 and ε = (2.92 ± 0.01) × 10⁴ for the 1 : 6 complex. It was shown that the reagent can be used for the potentiometric titration of osmium(IV). Conditions were determined for the successive titration of components of the osmium(IV)-ruthenium(IV) mixture.     

Das erste Oxoferrat(I): Zur Konstitution von K3[FeO2] und K3[NiO2]

The First Oxoferrate(I): On the Constitution of K₃[FeO₂] and K₃[NiO₂] Garnet-red single crystals of K₃[FeO₂] were obtained for the first time by heating intimate mixtures of K₆[CdO₄] and CdO (molar ratio 1:1.16) in closed Fe-cylinders at 450°C during 40 d. The same way of preparation via “reaction with the cylinder surface” was applied to prepare similarly coloured single crystals of K₃[NiO₂] (K₆CdO₄ in closed Ni-cylinders at 500°C during 49 d). The structure determination by four circle diffractometer data (MoKα , K₃[FeO₂]: 731 out of 731 I_o(hkl), R = 5.76%, R_w = 5.33%, K₃[NiO₂]: 755 out of 755 I_o(hkl), R = 8.70%, R_w = 4.25%) confirms the space groups P 4₁2₁2 and P 4₃2₁2, respectively. K₃[FeO₂]: a = 604.2(2) pm, c = 1 402.7(3) pm, Z = 4 K₃[NiO₂]: a = 603.6(1) pm, c = 1 405.2(2) pm, Z = 4. (powder data, standard deviations in parentheses) Essential feature of the structure are the dumb-bell-like anions [O? M? O]^3? (M = Fe, Ni). Their arrangement corresponds to a stuffed derivative of the KrF₂-type. Magnetic properties of K₃[FeO₂] were determined and cover the monovalence of Fe. MAPLE-calculations reveal the strong coincidence of monovalent VIIIb-cations.