Double quantum modulation NMR spectroscopy on spins with I = 1 in solids

NMR experiments with amplitude modulated rf pulses are introduced for the detection of double quantum coherences from spin I = 1 nuclei with large quadrupolar frequencies v_Q in solids. rf pulses of intensity v₁ and with modulation frequency v_m create effective irradiation fields of intensity $\text{1}\text{4}$v²₁/(v_Q-v_m) on the double quantum transition when v₁<¦v_Q-v_m¦?v_Q+v_m. ²D-NMR measurements on an oriented single crystal of deuterated malonic acid are presented.     

Theoretical treatment of intermediate electrolysis electrochemical detectors

A simple approach for deriving expressions for the limiting steady-state response of the open tubular electrode, under conditions of intermediate electrolytic yields, is described. This approach couples the principles of laminar fluid dynamics with the theory of the porous electrode reactor. The dependence of the limiting current, I₁, on flow rate, V_f, has the form of I₁ α V^m_f , with m ? $\text{1}\text{3}$, depending upon the electrolytic yield. The effects of electroactive species depletion upon the detector response are discussed. Experimental results are incorporated to support the theoretical conclusions. For a tubular electrode (4-cm long) the degree of conversion decreases from 0.21 to 0.03 and m decreases from 0.42 to 0.32 as the flow rate increases from 0.15 to 3.5 ml min^-1.     

Nephelauxetic effect in some lanthanide(III) complexes with 2-pyridineamidoxime

Diffuse reflectance spectra of tris-(2-pyridineamidoximato) lanthanide(III) chlorides, [Ln(PAO)₃] Cl₃, Ln = Pr, Nd, Sm, Eu, Dy and Ho, in the visible region have been recorded for the first time. Shifts (100–150 cm^?1) of their f ? f transitions have been observed towards lower wave numbers in relation to the lanthanide aquoions. These data have been used for evaluation of the nephelauxetic ratio β′ and the covalency parameters b^{$\text{1}\text{2}$}. Sublevels with J = 0 and J = $\text{1}\text{2}$ as well as hypersensitive bands, obeying the selection rules|ΔJ|?2,|ΔL|?2, have been considered. The results have been discussed in terms of weak covalent bonding between the lanthanide ion and the nitrogen atoms of the ligands.     

Determination of optical properties of hexagonal lithium iodate crystal by use of NQR and IR spectroscopy

The NQR Zeeman effect of ¹²⁷I (± $\text{1}\text{2}$ ←→ ± $\text{3}\text{2}$ transition) for the LiIO₃ crystal of hexagonal modification has been investigated, and the EFTG asymmetry parameter for nuclei of ¹²⁷I determined. Measurements of optical properties of the z-cut crystal in polarized light within the region of stretching vibrations and their overtones for IO^?₃ revealed that transmission (reflection) depends on the direction of the incident light wave electric vector. The results obtained indicate that crystals of LiIO₃ grown from aqueous solutions show anomalous biaxiality.     

Gradient expansion of the atomic kinetic energy functional

It is demonstrated that the ground-state atomic kinetic energy functional T[?], where ? is the electron density, can be computed to surprising accuracy from the truncated gradient expansion: T[?] = + T₂[?] + T₄[?], with T_o[?] = $\text{3}\text{10}$(3π²)$\text{2}\text{3}$ ∫ ?$\text{5}\text{3}$ d_τ, T₂ [?] = $\text{1}\text{72}$ ∫ (??)²?^?1 d_τ, and T₄ [?] given by the formula of Hodges. Calculations of T₀, T₂ and T₄ are reported for He with ? both the Hartree—Fock and a very accurate density, and for Ne, Ar and Kr with ? the Hartree—Fock density. For Kr, T₀ + T₂ + T₄ is within 0.3% of the exact Hartree—Fock T, with T₂/T₀ = 0.05, T₄/T₂ = 0.17.     

The enthalpies of formation of CH3Mn(CO)5 and of CH3Re(CO)5, and the strengths of the CH3Mn and CH3Re bonds

From measurements of the heats of iodination of CH₃Mn(CO)₅ and CH₃Re(CO)₅ at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔH^o_f[CH₃Mn(CO)₅, c] = ?189.0 ± 2 kcal mol^?1 (?790.8 ± 8 kJ mol^?1), ΔH^o_f[Ch₃Re(CO)₅,c] = ?198.0 ± kcal mol^?1 (?828.4 ± 8 kJ mo^?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn₂(CO)₁₀ and Re₂(CO)₁₀, values are derived for the dissociation energies: D(CH₃Mn(CO)₅) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol^?1 and D(CH₃Re(CO)₅) = 53.2 ± 2.5 kcal mol^?1. In general, irrespective of the value accepted for D(MM) in M₂(CO)₁₀, the present results require that, D(CH₃Mn) = $\text{1}\text{2}$D(MnMn) + 18.5 kcal mol^?1 and D(CH₃Re) = $\text{1}\text{2}$D(ReRe) + 30.8 kcal mol^?1.     

Frequency response to liquid density of a piezoelectric quartz crystal sensor with longitudinal wave

Elimination of longitudinal wave effect is an important aspect in the detection cell design, although such consideration is ignored in most of references. Three detection cells were designed to investigate the influence of longitudinal wave effect on the frequency response of a piezoelectric quartz crystal (PQC) to liquid density. In the cell with horizontally mounted quartz crystal, the air/liquid interface acts the reflection surface for the longitudinal wave. The variation in liquid height by regent addition or solvent evaporation can result in fluctuation in the oscillating frequency of the PQC. The influence of the longitudinal wave is more obvious in a test liquid of lower density. In the cell with perpendicularly mounted quartz crystal, the longitudinal wave is mainly reflected back by the inner wall body. The fine structure of plotting of frequency shift (Δf) versus (ρη)^1/2 shows a wave shape, which is different from the well-known linear relationship between of Δf and (ρη)^1/2, where ρ and η are the density and viscosity of the liquid, respectively. And wave-shaped frequency-temperature curves were observed. The longitudinal wave was a kind of potential error source in the PQC measurements. The longitudinal wave effect can be efficiently eliminated by using a rough reflection surface. After eliminating the influence of reflected longitudinal wave, the stability of the sensor PQC was much improved.     

Alkali metal solutions. Effect of cryptands on solubility and spectra in tetrahydrofuran,dioxane and toluene

By use of alkali cation complexing agents of the cryptand type, alkalimetals solutions can be prepared which contain different species depending on the nature of the solvent. In THF, in the presence of cryptand, M^? and E^?_solv have been observed, and quantitative values of the molar extinction coefficients, the temperature coefficients ($\text{dν}\text{d}\text{t}$, $\text{d?}\text{d}\text{t}$) and the oscillator strength (f) have been determined. In dioxane alone, only cesium gives a blue solution (Cs^?); in the presence of cryptand, Na, K, Rb and Cs dissolve well, but only the M^? absorption is observed.In toluene, the metals are normally insoluble and a cation complexing agent is required to dissolve them; in all the examined cases the addition of cryptand tended to give an aromatic radical anion. Blue solutions are obtained only for Na; in that case the solution exhibits ESR and optical behavior which indicates the presence of both anion radical and M^?.     

Gas phase oxidative-addition reactions of alkyl radicals at complexed cobalt(II) centres

Negative chemical ionisation mass spectrometry is used as a probe to identify reactions between hydrocarbon radicals and cornplexed cobalt(II) centres in the gas phase. Methane NCI mass spectra of a series of cobalt(II) complexes containing O₄, O₂N₂ and N₄ donor atom sets are characterised by adduct ions of the form [M + C_nH_2n+1]^? at m/z values above the molecular ion, [M]^?. Formation of such ionic species has been rationalised in terms of a one-electron oxidative-addition mechanism involving attack by hydrocarbon plasma-derived alkyl radicals at the metal centre prior to electron capture: Co^IIL_n + R^? → RCo^IIIL_n$\text{e}{}^{\mathrm{?}}$ [Co^IL_n]^?. The competing resonance electron attachment reaction: Co^IIL_n$\text{e}{}^{\mathrm{?}}$ also occurs within the ion source.     

Electrochemical study and polarographic determination of ranitidine

In the polarographic reduction of ranitidine, an H₂-antagonist of histamine, three waves are observed; their half-wave potentials and limiting currents depend strongly on the pH of the solution. The first and second waves are due to reduction of teh protonated, CHNO₂H⁺, and unprotonated, CHNO₂, nitroethene group of ranitidine, respectively; the origin of the third wave is unknown. The characteristics of the second and third waves are studied in acetic acid/acetate buffer at pH 5.5; the first wave does not appear at this pH. The second wave (E_{$\text{1}\text{2}$} = ?0.90 V, vs. Ag/AgCl) is useful for determining ranitidine in the range 2.4–4.9 × 10^?4 M by direct current polarography and in the range 2.5 × 10^?7?2.05 × 10^?5 M by differential pulse polarography.     

Electrochemical studies on monomeric ruthenium complexes.

Voltammetric studies on monomeric Ru(II) and Ru(III) complexes establish $\text{inter}$$\text{alia}$ reversible one-electron reduction and irreversible oxidation of [RuCl₃L₃] in contrast to [RuCl₄L₂]^?, and reversible one-electron oxidation of [RuCl₂(CO)_xL_4?x] (X = 1,2) for L = a variety of neutral ligands.     

Electrode kinetics of the metal complexes with aminopolycarboxylic acids: Part II. Cadmium-ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complexes

The d.c. polarographic current-potential curves of Cd(II)-EDTA complexes were examined in the pH range 0.5–10.0, to elucidate the mechanism of their electrode processes and to determine the relevant electrochemical kinetic parameters. It was shown that the first wave observed below pH 3 at ?0.58 to ?0.65 V vs. SCE is the reversible reduction wave of Cd(II) aquo-ion with kinetically-controlled limiting current, and the second wave observed above pH 1.5 at ?0.75 to ?1.21 V vs. SCE corresponds to the simultaneous irreversible reduction of four complex species, CdH₃L⁺, CdH₂L, CdHL^? and CdL^2?, where CdH_pL^(p?2)+ and L^4? denote the protonated complex species with p protons and the unprotonated EDTA ion, respectively. Analysis of the dependence of limiting current on the hydrogen ion concentration led to the conclusion that the preceding reaction determining the behaviour of limiting current is CdH₃L⁺?Cd²⁺+H₃L^? with k₃^d=6.3×10² s^?1 and k₃^f=3.3×10⁶ s^?1M^?1, where k₃^d and k₃^f are the dissociation and formation rate constants, respectively. On the other hand, from analysis of the dependence of half-wave potentials of the second wave on the hydrogen ion concentration, the kinetic parameters of the four complex species were evaluated, and are given in Table 1. Further, it was shown that the cathodic rate constants of these four charge transfer processes at some reference potential together with those of Cd(II)-HEDTA complexes fulfil the linear free energy relationship.     

Mechanistic Aspects of Inorganic Reactions. ACS Symposium Series 198 : (Ed. D.B. Rorabacher and J.F. Endicott), American Chemical Society,Washington DC, 1982, x + 486 pages, $ 58.95 ($ 48.95, U.S.A. and Canada). ISBN 0-5412-0734-8.

Norbornadiene (NBD) is more easily displaced from PtMe₂ (NBD) by other ligands than is cyclooctadiene (COD) from PtMe₂ (COD). cis-PtMe₂L₂ (L = py, $\text{1}\text{2}$tmen, $\text{1}\text{2}$en, NH₃, DMSO) have been prepared in this way. cis-PtMe₂py₂ is very reactive toward oxidative addition. Pyridine can usually be removed from the platinum(IV) products using acid. NBD is even more readily displaced from Pt(CF₃)₂ (NBD), giving cis-Pt(CF₃)₂L₂ (L = py, $\text{1}\text{2}$tmen, $\text{1}\text{2}$en, NH₃, DMSO, NCR, DMF, CN^?, I^?, acac^?). cis-Pt(CF₃)₂py₂ with CF₂I gives fac-Pt(CF₃)₃py₂I.     

Thermal investigation of diamine complexes of Zn(II) in the solid state

The complexes [Zn(en)₃]X2·n H₂O, where en = ethylenediamine, X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 1 or 0.5, and [Zn(tn)₂]X₂·n H₂O, where tn=1,3-diaminopropane, X=Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 0 or 0.25, have been synthesized and their thermal investigations carried out. The complexes were characterized by elemental analysis and IR spectral data. These complexes have been observed to decompose through several isolable as well as non-isolable complex species as intermediates during heating. [Zn(tn)₂]SO₄ undergoes solid-state phase transition in the temperature range 126–145°C. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) have been synthesized pyrolytically in the solid state from their corresponding mother diamine complexes. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) complexes decompose through non-isolable hemidiamine species. ZnX₂ (X = Cl^? or Br^?) complexes of tn undergo melting after formation of the monodiamine species. In contrast, the corresponding en complexes undergo melting at non-stoichiometric composition. Diamine (en or tn) is found to be bridging in all monodiamine (en or tn) complexes; whilst their mother complexes possess chelated en or tn. The thermal stability sequence of en and tn complexes of Zn(II) is ZnCl₂ < ZnBr₂ < ZnSO₄. ΔH values are reported for some steps of decomposition. Possible mechanistic paths have been reported for each step of decomposition.     

Anomaly in dispersion intermolecular potential produced by intense radation field

It is predicted that a gap of 2μE/3^{$\text{1}\text{2}$} appears in the dispersion potential for a pair of ground-state (identical) atoms, or molecules, at distance R such that ?δ + (4π?₀)^?1($\text{μ}{}^2\text{3}\text{R}{}^3$)(1 ? 3 cos²θ) = 0, where μ is the electric dipole moment, E is the field strength of an intense radiation field and θ is the angle between the polarization direction of the field and R. The detuning term Δ is ω₀?ω where ω₀ is the transition frequency of the atom or molecule, and ω is that of the field. The gap is of the order of 10¹¹ Hz when the intensity of the radiation field is a few $\text{MW}\text{cm}{}^2$.     

The enthalpies of formation of bis-(benzene)molybdenum and of bis-(toluene)tungsten

Microcalorimetric measurements at 520–523 K of the heats of thermal decomposition and of iodination of bis-(benzene)molybdenum and of bis-(toluene)tungsten have led to the values (kJ mol^?): ΔH^o_f[Mo(η-C₆H₆)₂, c] = (235.3 ± 8) and ΔH^o_f[W(η⁶-C₇H₈)₂, c] = (242.2 ± 8) for the standard enthalpies of formation at 25°C. The corresponding ΔH^o_f(g) values, using available and estimated enthalpies of sublimation, are (329.9 ± 11) and 352.2 ± 11) respectively, from which the metalligand mean bond-dissociation enthalpies, $\text{D}$(Mo—benzene) = (247.0 ± 6) and $\text{D}$(W—toluene) = (304.0 ± 6) kJ mol^?1, are derived.     

An improved absorption correction based on a Gaussian ionization distribution model for electron probe microanalysis

The electron range equation R, employed in a Gaussian absorption correction, is optimized making use of f(χ) values which were calculated from ionization distributions determined experimentally by Brown and Parobek. A new expression of R[R = $\text{(1 + 2}\text{h}\text{)}\text{(1 +}\text{h}$)2.59 × 10^?5(E^1.3₀ ?E^1.3_c)] g cm^?2 is proposed in this paper.The absorption correction using the new electron range equation R is applied to oxygen determination in several silicates and sulfates with greater accuracy than other methods. This equation also predicts one of the most accurate mean depths of ionization at an accelerating voltage of 25 kV for Zn and Cd tracers in Al, Cu, Ag and Au matrices.     

Extraction of indium(III) from chloride medium with 1-phenyl-3-methyl-4-acylpyrazol-5-ones. Synergic effect with high molecular weight ammonium salts.

The extraction of In(III) from 1M (Na,H)(Cl,ClO₄) media with 4-acylpyrazol-5-ones (HL) in toluene at 25°C is described by equilibria In ³⁺ + 3 $\text{HL}$ ? $\text{InL}{}_3$ + 3 H⁺ (log K = 1.48, 1.03, 0.87 with acyl = benzoyl, lauroyl, 2-thenoyl), InCl ²⁺ + 2 $\text{HL}$ ? $\text{InClL}{}_2$ + 2 H⁺ (log K = 0.26, ?0.45, ?0.35 respectively) and In³⁺ + m Cl^? ? InCl_m^(3-m)+ (log β_m available from literature). The extraction from 1M (Na,H)(Cl,NO₃) medium is enhanced by addition of aliquat (TOMA⁺,Cl^?) and the following synergic equilibrium takes place : $\text{InCl}{}_2$ + $\text{(TOMA}{}^{\mathrm{+}}$,Cl^?) ? $\text{(TOMA}{}^{\mathrm{+}}$, InCl₂L₂^? (log K = 5.49, 5.25, 5.21 respectively). Cl^? of (TOMA⁺,Cl^?) is exchanged by NO₃^? with the equilibrium constant log K = 1.50. If (TOMA⁺,Cl^?) is replaced by tri-n-octylammonium chloride, the synergic effect is largely reduced (log K = 4.17 with acyl = benzoyl). The extraction from chloride solutions containing ClO₄^? remains unchanged by addition of ammonium salts.     

Synthesis of homoleptic tris(organo-chelate)iridium(III) complexes by spontaneous ortho-metallation of electronrich olefin-derived N,N′-diarylcarbene ligands and the X-ray structures of fac-[Ir{CN(C6H4Me-p) (CH2)2NC6H3Me-p}3] and mer-Ir{CN(C6H4Me-p)(CH2)2NC6H3Me-p}2 {CN(C6H4Me-p)(CH2)2NC6H4Me-p}Cl (a product of HCl cleavage)

Treatment of [{Ir(COD)(μ-Cl)}₂] with excess of the electron-rich olefin [$\text{CN(Ar)(CH}{}_2\text{)}{}_2\text{N}$Ar]₂ (abbreviated as (L^Ar)₂, Ar = C₆H₄Me-p or C₆H₄OMe-p) affords the ortho-metallated tricycle [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₃], which for Ar = C₆H₄Me-p (Ia) with HCL yields [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₂(L^Ar)]Cl (IV); X-ray data show that in IV there is an unexpectedly close Ir?C(o-aryl) contact (2;52(1) Å) involving the “free” L^Ar which compares with an IrC(o-aryl) distance of 2.09(3) Å in Ia or 2.07(3) Å in the ortho-metallated L^Ar ligand of complex IV.