Preparation and characterization of Co(II), Ni(II) and Cu(II) complexes of a ligand containing 1,3,4-thiadiazole groups

(1R,2R)-1,2-bis-(5-amino-1,3,4-thiadiazole-2-yl)ethane-1,2-diol (L) has been prepared by the reaction of thiosemicarbazide with (2R,3R)-(+)-tartaric acid (I) and phosphorous oxychloride, and its complexes with Co(II), Ni(II) and Cu(II) have been obtained. The structures of the ligand and its complexes have been established by i. r., ¹H- and ¹³C-n.m.r. spectra, u.v.–vis–nir spectroscopy, elemental analyses, T.g.-D.t.a. and magnetic susceptibility measurements.     

The effect of thermal pretreatment on the electrochemical response for palladium in aqueous media

Previous work on the electrochemistry of palladium in aqueous acid solution demonstrated the existence of two multilayer hydrous oxide reduction peaks, one at ca. 0.24 V and another at ca. 0.55 V vs. RHE, plus the presence of a reversible active surface state transition at ca. 0.24 V. In the present work with thermally activated palladium it was observed that, in agreement with the hydrous oxide reduction behaviour of the system, there is a second active state transition at E≥ca. 0.45 V. In most of its reactions in aqueous acid solution, apart from its unusual capacity to absorb hydrogen, palladium exhibits properties very similar to those of platinum; however, palladium seems to be more prone to dissolution and subsurface oxygen formation. Also the premonolayer oxidation responses of these two metals are often different as the more active state of the palladium surface is not as readily generated as that of platinum. The electrocatalytic properties of palladium, as reported earlier, correlate quite well with the hydrous oxide and premonolayer oxidation behaviour of this electrode system. Electronic Publication     

Tetranuclear Pt<Subscript>2</Subscript>Cu<Subscript>2</Subscript> Complex with a Staircase-Shaped Chain Aggregate in the Solid State

The reaction of the tetranuclear cyanide aquo complex [{Pt(CN)₄Cu(bipy)(H₂O)}₂]· 2H₂O with aqueous ammonia produces the new tetranuclear ammino-containing product [{Pt(CN)₄Cu(bipy)(NH₃)}₂] (1), with terminal cyanide groups and with NH₃ coordinated to the Cu atom. The distorted trigonal bipyramidal coordination about copper in 1 differs from the square-pyramidal coordination present in the starting material. The bipyridine ligand in 1 is nearly perpendicular to the tetranuclear core of the molecule, as opposed to its coplanar disposition in the aquo complex. The two platinum atoms of the tetranuclear core in 1 form Pt···Pt interactions of 3. 2390(8) Å with platinum atoms of neighboring molecules, producing an echelon-shaped supramolecular chain held together by staggered (CN)₄Pt···Pt(CN)₄ linkages, an aggregate structure which does not have a precedent in chemistry derived from the Pt(CN)₄ building block.     

Adventages and limits on usage of thermal methods in complex systems

In order to increase the nutrition value of bread, one of the most commonly used foodstuff all over the world, different additives are used in bread processing. In this paper we describe the thermal changes in bread and that of with 0.5% crude soybean lecithin additive. Their thermal stability has been investigated by TG, DSC and EGD methods. The thermal changes were also followed of soy products, lecithin and lysine, ingredients used as bread additives in order to check if they may suffer any thermal degradation during the baking process. The data obtained can be of use only for qualitative conclusions. According to the obtained data at the usual bread baking temperature only the additives in crust may partly decompose while in the crumb, at lower temperatures the additives, due to baking, are not damaged. The thermal methods give a possibility for rapid estimation of processes induced by heat effects in additives during the baking, and they are suitable to detect the changes during the bread-making procedure. However, they are neither suitable to provide any quantitative data on these changes nor facts affecting the nutrition value and of the bread.     

Local structure and photoluminescent characteristics of Eu<Superscript>3+</Superscript> in ZnO–SiO<Subscript>2</Subscript> glasses

The photoluminescence properties of xZnO–(100−x)SiO₂ (x = 0, 5, 10, 20) containing 1% Eu₂O₃ prepared by a sol–gel method were systematically investigated. The results indicated that the relative proportion of f–f transitions to charge transfer (CT) absorption decreased with the increase of ZnO concentration. The intensity of ⁵D₀–⁷F_J transitions of Eu³⁺ ions was enhanced with the increase of ZnO content due to local structure changes and decreased quantities of Eu³⁺ ions clusters. The results of fluorescence line narrow (FLN) spectra indicated that Eu³⁺ ions occupied one site in SiO₂ glass and two sites in ZnO–SiO₂ glasses. The second-order crystal field parameters were calculated. B₂₀ and B₂₂ for site 1 increased with excitation energy, while ones hardly changed for site 2.     

Ruthenium Carbonyl Cluster Complexes with Phenylgermyl Ligands from the Reactions of Ph<Subscript>3</Subscript>GeH with Ru(CO)<Subscript>5</Subscript> and Ru<Subscript>3</Subscript>(CO)<Subscript>12</Subscript>

Four new triphenylgermylruthenium carbonyl compounds HRu(CO)₄GePh₃, 14; Ru(CO)₄(GePh₃)₂, 15; Ru₂(CO)₈(GePh₃)₂, 16; and Ru₃(CO)₉(GePh₃)₃(μ-H)₃, 17 were obtained from the reaction of Ru(CO)₅ with Ph₃GeH in hexane solvent at reflux, 68 °C. The major product 14 was formed by loss of CO from the Ru(CO)₅ and an oxidative addition of the GeH bond of the Ph₃GeH to the metal atom. This six coordinate complex contains one terminal hydrido ligand. Compound 15 is formed from 14 and contains two trans-positioned GePh₃ ligands in the six coordinate complex. Compound 16 contains two Ru(CO)₄(GePh₃) fragments joined by an Ru–Ru single bond. Compound 17 contains a triangular cluster of three ruthenium atoms with three bridging hydrido ligands and one terminal GePh₃ ligand on each metal atom. When heated to 125 °C, 14 was converted to the new triruthenium compound Ru₃(CO)₁₀(μ-GePh₂)₂, 18. Compound 18 consists of a triangular tri-ruthenium cluster with two GePh₂ ligands bridging two different edges of the cluster and one bridging CO ligand. Ru₃(CO)₁₂ was found to react with Ph₃GeH at 97 °C to yield three products: 15, and two new compounds Ru₃(CO)₉(μ-GePh₂)₃, 19 and Ru₂(CO)₆(μ-GePh₂)₂(GePh₃)₂, 20 were obtained. Compound 19 is similar to 18 having a triangular tri-ruthenium cluster but has three bridging GePh₂ ligands, one on each Ru–Ru bond. Compound 20 contains only two ruthenium atoms joined by a single Ru–Ru bond that has two bridging GePh₂ ligands and a terminal GePh₃ ligand on each metal atom. All compounds were characterized by a combination of IR, ¹H NMR, single-crystal X-ray diffraction analyses. This report is dedicated to Professor Dieter Fenske on the occasion of his 65th birthday for his many pioneering contributions to the chemistry of metal chalcogenide cluster complexes.     

Monthly sea surface temperature records reconstructed by δ<Superscript>18</Superscript>O of reef-building coral in the east of Hainan Island,South China Sea

Stable oxygen isotopic compositions of a coral colony ofPorites lutea obtained on a core allowed the reconstruction of a 56-a (1943–1998) proxy record of the sea surface temperatures. This coral δ¹⁸O data are from the east of Hainan Island water (22°20’N, 110°39’E), South China Sea. The relationship between δ¹⁸O in the skeletal aragonite carbonate and the sea surface temperature (SST) is SST = -5.36 δ¹⁸O_PDB-3.51 (r = 0.73,n = 470), dδ¹⁸O/d(SST) = -0.187?/ °C; and the thermometer was set at monthly resolution. The 56-a (1943–1998) proxy record of the sea surface temperatures reflected the same change trend in the northern part of South China Sea as the air temperature change trend in China.     

2-[3-(Trifluoromethyl)phenyl]furo[3,2-b]pyrroles: synthesis and reactions

The synthesis and reactions of methyl 2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrole-5-carboxylate (1a) are described. Upon reaction with methyl iodide, benzyl chloride, or acetic anhydride, this compound gave N-substituted products 1b-d. By hydrolysis of compounds 1a-c, the corresponding acids 2a-c were formed, or by reaction with hydrazine-hydrate, the corresponding carbohydrazides 3a-c were formed. By heating 2-[3-(trifluoromethyl)phenly]-4H-furo[3,2-b]pyrrole-5-carboxylic acid (2a) in acetic anhydride, 4-acetyl-2-[3-(trifluoromethyl)phenyl]furo[3,2-b]pyrrole (4) was formed. By hydrolysis of 4, 2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrole (5a) was formed, and reactions with methyl iodide or benzyl chloride gave N-substituted products 5b-c. The reaction of 4 with dimethyl butynedioate gave substituted benzo[b]furan 6. Compound 3a reacted with triethyl orthoesters giving 7a-c, which afforded with phosphorus (V) sulphide the corresponding thiones 8a-c. The thiones 8a-c reacted with hydrazine hydrate to form hydrazine derivatives 9a-c. The reaction of triethyl orthoformiate with compounds 9a-c led to furo[2′,3′: 4,5]pyrrolo[1,2-d][1,2,4]triazolo[3,4-f][1,2,4]triazines 10a-c. Hydrazones 11a-c were formed from 3a-c and 5-[3-(trifluoromethyl)phenyl]furan-2-carboxaldehyde. The effect of microwave irradiation on some condensation reactions was compared with “classical” conditions. The results showed that microwave irradiation shortens the reaction time while affording comparable yields.     

Copper(II) ion sensor based on electropolymerized undoped conducting polymers

A solid state copper(II) ion sensor is reported based on the application of electropolymerized undoped (neutral) polycarbazole (PCz) and polyindole (PIn) modified electrodes. The new sensor shows high selectivity to Cu²⁺ ions with a detection limit of 10^–5 M. PCz and PIn are formed respectively by the anodic oxidation of 50 mM carbazole and 5 mM indole monomers in dichloromethane containing 0.1 M tetrabutylammonium perchlorate on a platinum electrode using a single compartment cell. Potentiostatic polymerization of both the monomers are carried out at 1.3 V and 1.0 V vs. Ag/AgCl, respectively. Perchlorate ions were electrochemically removed from the polymer films by applying – 0.2 V vs. Ag/AgCl. Polymer-coated electrodes are incubated in 1 M KCl solution for 8 h followed by incubation in distilled water for 2 h before using as a metal ion sensor. The undoped PCz and PIn electrodes were found to be highly selective and sensitive for Cu²⁺ ions with little selectivity for Pb²⁺ and negligible response towards Ag⁺, Hg²⁺, Cu⁺, Ni²⁺, Co²⁺, Fe²⁺, Fe³⁺ or Zn²⁺. Potentiometric responses for Cu²⁺ ions are recorded for both the sensor electrodes together with a double-junction Ag/AgCl reference electrode. Calibration curves for Cu²⁺ are reported for both ion sensors. The polymer-modified electrodes were found to be stable for several weeks. Electronic Publication