Bis(η-pentamethylcyclopentadienyl)-and(ηcyclopentadienyl) (η-pentamethylcyclopentadienyl)-platinium dications: Pt(IV) metallocenes

Reaction of [Pt₂(η⁵-C₅Me₅)₂(η-Br)₃]³⁺(Br⁻)₃ with C₅R₅H (R = H,Me) in the presence of AgBF₄ gives the first platinocenium dications, [Pt(η⁵-C₅Me₅)(η⁵-C₅R₅)]²⁺(BF₄⁻ )₂. On electrochemical reduction, [pt(η⁵-C₅Me₅)₂]²⁺ yields [Pt(η⁴-C₅Me₅H)(η²-C₅Me₅)]+ BF₄⁻. kw]Cyclopentadienyl; Metallocenes; Platinum; Electrochemistry     

Synthesis and some heterocyclisation reactions of CF2H- and CF2Cl-substituted 1,1-dicyanoethylenes

New CF₂X-analogues of 1,1-dicyano-2,2-bis(trifluoromethyl)ethylene (1) (X=H, Cl) were synthesised by the condensation of polyfluoroketones with malononitrile followed by dehydration using thionyl chloride (or phosphorus pentoxide). The heterocyclisation reactions of new CF₂X-analogues of 1,1-dicyano-2,2-bis(trifluoromethyl)ethylene with amidines, 5-aminopyrazoles and 3-methyl-2-pyrazolin-5-ones were systematically investigated.     

Approaches to understanding the searching behavior of CrossFire users

Due to the high costs of purchasing, supporting and training users of desktop chemical information systems, it is important to understand users' behavior in order that deficiencies in their search efficiency and effectiveness can be identified and addressed. CrossFire generates comprehensive log files that can be examined to determine the nature of search activity. At GSK (GlaxoSmithKline) a Log File Parser, CrossParse, has been developed in Visual Basic that enables analysis by individual user name, groups of users or the whole user population. Log files can be analyzed for occasions when specific structural features are built, specific types of search are done and how the results are manipulated. CrossParse produces output that can be saved and analyzed within Microsoft Excel. It also allows determination of numbers of active concurrent users on the CrossFire system. CrossParse has been used at GSK (ex-SmithKline Beecham sites) to examine the search behavior of medicinal and synthetic chemists. Additionally, it has been used by MIMAS (Manchester Information and Associated Services) to compare the search behavior of trained and untrained users in the higher education community and to identify any areas where improvements to training can be made. Use of CrossParse in both organizations has allowed identification of areas where users may have difficulties using CrossFire. This will provide valuable feedback to MDL Inc., the authors of the CrossFire application, and guide them in enhancing CrossFire.     

Synthesis and properties of 1,5-diaminotetrazole

An effective method was developed for preparation of 1,5-diamino tetrazole from thiosemicarbazide and sodium azide in the presence of lead(II) oxide and ammonium chloride in DMFA. Its physical properties and certain reactions were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1683–1686, December, 1984.     

Structure of ions [ZnNCR]+ and [Zn(NCR)2]+ (R = H,CH3) in the gas phase

Structures of [ZnNCR]⁺ and [Zn(NCR)₂]⁺ ions (R = H, Me), which are abundant in the mass spectra of many types of coordination compounds, were studied by the MNDO method. In all cases the most stable isomers correspond to the zinc ion coordinated with the nitrogen(s) of the nitrile ligand. For [Zn(NCR)₂]⁺, the N-Zn-N angles are ～108°.     

Photoinduced electron transfer in self-assembled monolayers of porphyrin-fullerene dyads on ITO

Two porphyrin-fullerene dyads were synthesized to form self-assembled monolayers (SAMs) on indium-tin oxide (ITO) electrode, with either ITO-porphyrin-fullerene or ITO-fullerene-porphyrin orientations. The dyads contain two linkers for connecting the porphyrin and fullerene moieties and enforcing them essentially to similar geometries of the donor-acceptor pair, and two linkers to ensure the attachment of the dyads to the ITO surface with two desired opposite orientations. The transient photovoltage responses (Maxwell displacement charge) were measured for the dyad films covered by insulating LB films, thus ensuring that the dyads interact only with the ITO electrode. The direction of the electron transfer was from the photoexcited dyad to ITO independent of the dyad orientation. The response amplitude for the ITO-fullerene-porphyrin structure, where the primary intramolecular electron-transfer direction coincides with the direction of the final electron transfer from the dyad to ITO, was 25 times stronger than that for the opposite ITO-porphyrin-fullerene orientation of the dyad. Static photocurrent measurements in a liquid electrochemical cell, however, show only a minor orientation effect, indicating that the photocurrent generation is controlled by the processes at the SAM-liquid interface.     

Quantum chemical study of the reaction of NH4+ with alkylmercury halides in the gas phase

Calculations on the thermochemistry of reactions between NH₄⁺ ions and EtHgX molecules (X = Cl, Br, I) were performed by the MNDO method. The calculations showed the possible existence of two stable isomers of composition [EtHgX, NH₄]⁺ namely [EtHgX…?HNH₃]⁺ and [EtHg(NH₃)XH]⁺. Protonation of EtHgX and of CH₂?CHHgX by NH₄⁺ is characterized by high exothermicity.     

Transformation of the Photoacoustic Signal after Treatment of Barley Leaves with Methylviologen or High Temperatures

Abstract— The photoacoustic (PA) signal at the modulation frequency of 35 Hz was studied in MV-treated barley leaves or leaves preheated at different temperatures. Saturating illumination enhanced the magnitude of the PA signal in MV-treated leaves in contrast with the opposite result usually found in untreated intact leaves where saturating illumination abolishes the photobaric component of the PA signal due to oxygen evolution and thus decreases the total PA signal. A linear relationship was found between the changes induced by continuous background light in the negative response of PA signal to saturating light in intact leaves and in the positive response in MV-treated leaves. A linear relationship was also observed in MV-treated leaves between the positive changes in the PA signal and the changes in the rate of electron transport through photosystem II (PSII) calculated from chlorophyll fluorescence data. The conclusion was drawn that only the thermal component contributes to the PA signal measured at low modulated frequency in MV-treated leaves because the enhanced O2 uptake provides a zero net oxygen exchange by superimposing with O2 evolution. The leaves preheated at temperatures above 43°C demonstrated the positive response of the PA signal to saturating light at 35 Hz. In leaves preheated at 41.5°C, the first and second saturating pulses induced the enhancement of PA signal, whereas other pulses decreased the PA signal due to onset of oxygen evolution. The energy storage activity measured in the absence of oxygen evolution in heat-treated leaves is proposed to be associated with cyclic electron transport activities around PSII and PSI.     

Crystal and molecular structure of 9-methyl-9-phenyl-9,10-dihydro-9-sila-3-azaanthrone

The crystal and molecular structure of 9-methyl-9-phenyl-9,10-dihydro-9-sila-3-azaanthrone has been determined from three-dimensional X-ray diffraction data. The title compound crystals are monoclinic, space group P2₁/b, a = 12.818(2), b = 16.508(2), c = 7.694(1) Å,γ = 105°, 34′(2), Z = 4 and D_cal = 1.278 g cm^?3. The structure was determined by direct methods and refined by full-matrix least-squares calculations in the block-diagonal anisotropic approximation for non-hydrogen atoms to R = 0.043 for 2190 independent reflections, registered at room temperature. This is the first crystal structure determination of a Si-dihydroanthracene derivative with two heterocycles and a planar carbon atom in the C10-position. The tricyclic fragment takes up a planar configuration, the silicon atom having a tetrahedral surrounding, with an endocyclic angle of 103.7(1)° and average bond length SiC, 1.862(1) Å. The CO, 1.220(2) Å, bond length in the carbonylic group exactly corresponds with the double bond length. Average distance NC is 1.335(3) Å, angle CNC, 116.5(2)°.     

Analysis of hot D2O emission using spectroscopically determined potentials

Fourier transform emission spectra of D2O vapor were recorded at a temperature of 1500 degrees C in the wavenumber range 380-1880 cm(-1). 15 346 lines were measured, of which the majority were identified as belonging to D2O. The spectrum was analyzed using variational nuclear motion calculations based on spectroscopically determined potential-energy surfaces. Initial assignments were made using a potential surface obtained by fitting a high accuracy ab initio potential. The new assignments were used to refine the potential surface, resulting in additional assignments. A total of 6400 D2O transitions were assigned and 2144 new D2O energy levels were obtained. Transitions involving the 4nu2 and 5nu2 bending states, with band origins of 4589.30 (+/-0.02) and 5679.6 (+/-0.1) cm(-1), respectively, were assigned for the first time.