Effect of preparation on Hg−Ba−Ca−Cu−O superconductors

Some main features of the non-linear synthesis process are described by theoretical considerations. Results of typical preparation methods are compared to each other and to those obtained by the experiments designed specially for the study of the effect of synthesis on the superconducting properties of Hg−Ba−Ca−Cu−O compounds. As is shown, the controlled Hg-vapour pressure method, the sealed tube with phase formation procedure, the high-pressure synthesis and the freeze-drying method seem to be unambiguously reliable to provide high-quality samples. Significant deviations from these fundamental synthesis routes can lead to significant deviations of superconducting parameters.     

Effect of preparation on Hg−Ba−Ca−Cu−O superconductors

Some main features of the non-linear synthesis process are described by theoretical considerations. Results of typical preparation methods are compared to each other and to those obtained by the experiments designed specially for the study of the effect of synthesis on the superconducting properties of Hg?Ba?Ca?Cu?O compounds. As is shown, the controlled Hg-vapour pressure method, the sealed tube with phase formation procedure, the high-pressure synthesis and the freeze-drying method seem to be unambiguously reliable to provide high-quality samples. Significant deviations from these fundamental synthesis routes can lead to significant deviations of superconducting parameters.     

Generalized contraction mapping principles in probabilistic metric spaces

We give an improvement of Theorem 1 from [2] with a quite different approach, which enable us to prove that the fixed point is also globally attractive. In Theorem 2.11 a further generalization is obtained for a complete Menger space (S,F,T), where T belongs to a more general class of continuous t-norms than in the previous case where T=T _M (=min). Theorem 3.2 is a generalization of Theorem 2 from [2]. Thereafter the notion of a generalized C-contraction of Krasnoselski's type is introduced and a fixed point theorem for such mappings is proved. An application in the space S(Ω, K, P) is given.     

A characterization of graphs without long induced paths

In a connected graph define the k-center as the set of vertices whose distance from any other vertex is at most k. We say that a vertex set S d-dominates G if for every vertex x there is a y ∈ S whose distance from x is at most d. Call a graph P_t-free if it does not contain a path on t vertices as an induced subgraph. We prove that a connected graph is P_2k-1-free (P_2k-free) if and only if each of its connected induced subgraphs H satisfy the following property: The k-center of H (k - 1)-dominates ((k - 2)-dominates) H. Moreover, we show that the subgraph induced by the (t - 3)-center in any P_t-free connected graph is again connected and has diameter at most t - 3.     

Photoelectron spectroscopy and thermochemistry of tert-butylisocyanide-substituted cobalt tricarbonyl nitrosyl

A new organometallic complex, Co(CO)2NOtBuNC, was synthesized and investigated by photoelectron spectroscopy (PES) and threshold photoelectron photoion coincidence (TPEPICO) spectrometry in order to determine its ionization energy as well as the bond energies in the ionic forms. The assignment of the nine peaks in the PES was based on Kohn-Sham molecular orbital energies, and an adiabatic ionization energy of 7.30 +/- 0.05 eV was determined. In the TPEPICO experiment, the following 0 K onsets were determined for the various fragment ions: CoCONOtBuNC+ (8.17 +/- 0.05 eV); CoNOtBuNC+ (9.01 +/- 0.05 eV); and CotBuNC+ (10.42 +/- 0.05 eV). Because the photon source did not extend above 14 eV, we could not observe the bare Co+ ion in the experiment. The heat of formation of the CotBuNC+ ion was estimated by ab initio and DFT calculations of the CoL+ + tBuNC --> CotBuNC+ + L (L = CO, NO, NH3, H2O, PMe3) substitution enthalpies.     

Preparation of Polymer‐Metal Composites via In Situ Decomposition of Metal Salts by Frontal Polymerization

Composites containing powdered zinc, and zinc/lead acetate were prepared via frontal polymerization. In the case of the acetates, elemental metal was formed in an in situ decomposition process. The local area function was used to demonstrate the distribution of fillers, and the uniformity of the area fraction for the quantitative characterization of the distribution. With the use of metal acetates, composites of uniform metal distribution can be produced, unlike in systems with metal powder, where the metal particles are enriched at the margin of the sample. It can be established that the specific direct‐current resistance significantly decreases in AA‐TGDMA composites by the addition of zinc acetate, compared to that of the initial monomer mixture. On heating, the unreacted zinc acetate decomposes further, which results in the further decrease in electrical resistance.

     

Dissociation dynamics of sequential ionic reactions: heats of formation of tri-, di-, and monoethylphosphine

The sequential ethene (C2H4) loss channels of energy-selected ethylphosphine ions have been studied using threshold photoelectron photoion coincidence (TPEPICO) spectroscopy in which ion time-of-flight (TOF) distributions are recorded as a function of the photon energy. The ion TOF distributions and breakdown diagrams have been modeled in terms of the statistical RRKM theory for unimolecular reactions, providing 0 K dissociation onsets, E0, for the ethene loss channels. Three RRKM curves were used to model the five measurements, since two of the reactions differ only by the internal energy of the parent ion. This series of dissociations provides a detailed check of the calculation of the product energy distribution for sequential reactions. From the determined E0's, the heats of formation of several ethylphosphine neutrals and ions have been determined: Delta(f)H degrees 298K[P(C(2)H(5))3] = -152.7 +/- 2.8 kJ/mol, Delta(f)H degrees 298K[P(C(2)H(5))3+] = 571.6 +/- 4.0 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2] = -89.6 +/- 2.1 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2+] = 669.9 +/- 2.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)] = -36.5 +/- 1.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)+] = 784.0 +/- 1.9 kJ/mol. These values have been supported by G2 and G3 calculations using isodesmic reactions. Coupled cluster calculations have been used to show that the C2H4 loss channel, which involves a hydrogen transfer step, proceeds without a reverse energy barrier.     

Application of inductively coupled plasma sector field mass spectrometry for low-level environmental americium-241 analysis

An improved and novel sample preparation method for ²⁴¹Am analysis by inductively coupled plasma sector field mass spectrometry has been developed. The procedure involves a selective CaF₂ pre-concentration followed by an extraction chromatographic separation using TRU™ resin. The achieved absolute detection limit of 0.86 fg (0.11 mBq) is comparable to that of alpha spectrometry (0.1 mBq) and suitable for low-level environmental measurements. Analysis of different kinds of environmental standard reference materials (IAEA-384 - Fangataufa lagoon sediment, IAEA-385 - Irish Sea sediment and IAEA-308 - Mixed seaweed from the Mediterranean Sea) and alpha spectrometry were used to validate the procedure. The chemical recovery of sample preparation ranged between 72 and 94%. The results obtained are in good agreement with reference values and those measured by alpha spectrometry. The proposed method offers a rapid and less labor-intensive possibility for environmental ²⁴¹Am analysis than the conventionally applied radioanalytical techniques.     

Dimerization processes of square planar [PtII(tbpy)(dithiolato*)]+ radicals

The preparation and structural characterization of the neutral, square planar complexes [PtII(tbpy)(A)] (1), [PtII(tbpy)(B)] (2), and [PtII(PPh3)2(B)] (3) have been accomplished, where (tbpy) = 4,4'-di-tert-butylpyridine, (A)2- = 3,6-bis(trimethylsilyl)-1,2-benzenedithiolate(2-), and (B)2- = 1,2-bis(4-tert-butylphenyl)ethylene-1,2-dithiolate(2-) and (A*)1- and (B*)1- represent the corresponding monoanionic radicals. Electrochemical and chemical one-electron oxidation of 1 and 2 in CH2Cl2 solution affords the monomeric monocations [PtII(tbpy)(A*)]+ (1a) and [PtII(tbpy)(B*)]+ (2a), both of which possess an S = 1/2 ground state. The corresponding spin doublet monocationic dimers [PtII2(tbpy)2(A)(A*)]+ (1b) and [PtII2(tbpy)2(B)(B*)]+ (2b) were electrochemically generated in solution (50% oxidation) and identified by X-band EPR spectroscopy. Complete one-electron oxidation of 1 and 2 yielded the diamagnetic dimers [PtII2(tbpy)2(A*)2]2+ (1c) and [PtII2(tbpy)2(B*)2]2+ (2c) which are in equilibrium with the corresponding paramagnetic monomers 1a and 2a in solution. The crystal structure of [PtII2(tbpy)2(B*)2](PF6)2.3CH2Cl2 (2c) revealed a centrosymmetric, lateral dimer whose bridging part is a PtII2(mu2-S)2 rhomb; the metal ions possess a square based pyramidal geometry. Solid-state sulfur K-edge X-ray absorption spectra of 1, 2, 2a, 2c, and [PtII(B*)2]0 (4) have been recorded, which clearly show that a sulfur-centered radical (B*)1- is present in 2a, 2c, and 4. The absence of ligand-based radicals in 1 and 2 is also clearly established. One-electron oxidation of [Pt(PPh3)2(B)] (3) afforded only the spin doublet species [PtII(PPh3)2(B*)]+ (3a); no dimer formation was detected. Synthesis and crystal structure of square planar [PtII(B*)2]0.thf are also reported.     

Molecular and electronic structure of square-planar gold complexes containing two 1,2-Di(4-tert-butylphenyl)ethylene-1,2-dithiolato ligands: [Au(2L)2]1+/0/1-/2-. A combined experimental and computational study

From the reaction of in situ generated 1,2-di(4-tert-butylphenyl)ethylene-1,2-dithiol, 2LH2, and Na[AuCl4].2H2O in 1,4-dioxane, green brown crystals of diamagnetic [N(n-Bu)4][AuIII(2L)2] (1) were obtained. As shown by cyclic voltammetry, 1 is a member of an electron-transfer series comprising the dianion [AuII(2L)2]2-, the monoanion [AuIII(2L)2]-, the neutral species [AuIII(2L*)(2L)]0 <--> [AuIII(2L)(2L*)]0, and the monocation [AuIII(2L*)2]+. (2L*)1- represents the pi radical anion (Srad = 1/2) of the one-electron oxidized closed-shell dianion (2L)2-. Oxidation of 1 in CH2Cl2 with ferrocenium hexafluorophosphate affords green, paramagnetic microcrystals of [AuIII(2L*)(2L)] <--> [AuIII(2L)(2L*)] (2) (S = 1/2). Complexes 1 and 2 have been characterized by X-ray crystallography. Both species possess square-planar monoanions and neutral molecules, respectively. From the oxidation reaction of 1 or [N(n-Bu)4][AuIII(3L)2] with 2-3 equiv of [NO]BF4 in CH2Cl2, a green solution of [AuIII(2L*)2]+ and green microcrystals of [AuIII(3L*)2]BF4 (3) were obtained, respectively; (3L)2- represents the dianion 1,2-di(4-diphenyl)ethylene-1,2-dithiolate, and (3L*)1- is its pi radical monoanion. The electronic structures of this series of gold species have been elucidated by UV-vis, EPR spectroscopies, and DFT calculations. It is shown computationally by density functional theoretical (DFT) methods that the electronic structure of [AuIII(1L*)2]+ is best described as a singlet diradical (St = 0); the ligand mixed valency in the neutral species 2 is of class (III) (delocalized); the monoanion in 1 contains a AuIII ion and two closed-shell dianionic ligands; and the corresponding dianions [Au(L)2]2- are best described as an intermediate AuII/AuIII species with a metal-ligand delocalized SOMO (25% Au 5d, 75% 3p of four S atoms). (1L)2- is the dianion 1,2-di(phenyl)ethylene-1,2-dithiolate, and (1L*)1- is the pi radical monoanion. The neutral species [PdII(2L*)2] (4) has also been synthesized and characterized by X-ray crystallography. Its electronic structure is the same as described for [AuIII(1L*)2]+ (singlet diradical), whereas that of the monoanion [PdII(2L*)(2L)]- <--> [Pd(2L)(2L*)]- corresponds to that of the neutral gold complex 2. Anodic oxidation of the analogous monoanion [AuIII(mnt)2]-, where mnt = maleonitriledithiolate, gave the neutral complex [Au(mnt)(mnt*)] (E1/2 = 0.91 V vs Fc+/Fc). The optical and EPR spectroscopies of [Au(mnt)(mnt*)] were consistent with those observed for the corresponding di(tert-butylphenyl)ethylenedithiolate complex 2.