Ternary metal complexes of anionic and neutral pyridoxine (vitamin B6) with 2,2'-bipyridine. Syntheses and x-ray structures of (pyridoxinato)bis(2,2'-bipyridyl)cobalt(III) perchlorate and chloro(2,2'-bipyridyl)(pyridoxine)copper(II) perchlorate hydrate

Ternary metal complexes involving vitamin B6 with formulas [CO",(PN-H)](anCdI [OC)'(bpy)(PN)Cl]C10(.bpHy 0 = 2,2'-bipyridine, PN = neutral pyridoxine, PN-H = anionic pyridoxine) have been prepared for the first time and characterized by means of magnetic and spectroscopic measurements. The crystal structures of the compounds have also been determined. [CO(PN-H)](CcryIsOta,l)lize s in the space group P2,/c with a = 18.900 (3) A, b = 8.764 (1) A, c = 20.041 (2) A,p = 116.05 (l)', and Z = 4 and [Cu(bpy)(PN)C1]C104-H20in the space group Pi with a = 12.136 (5) A, b = 13.283 (4) A,c = 7.195 (2) A, a = 96.91 (Z)', 0 = 91.25 (3)', y = 71.63 (3)', and Z = 2. The structures were solved by the heavy-atom method and refined by least-squares techniques to R values of 0.080 and 0.042 for 3401 and 2094 independent reflections, respectively. Both structures consist of monomeric units. The geometry around Co(II1) is octahedral and around Cu(I1) is distorted square pyramidal. In [CO(PN-H)]t(wCo IoxOy~ge)n~s ,fro m phenolic and 4-(hydroxymethyl) groups of PN-H and two nitrogens from each of two bpy's form the coordination sphere. In [Cu(bpy)(PN)C1]C104.H20o ne PN and one bpy, with the same donor sites, act as bidentate chelates in the basal plane, with a chloride ion occupying the apical position. In both structures PN and PN-H exist in the tautomeric form wherein pyridine N is protonated and phenolic 0 is deprotonated. However, a novel feature of the cobalt compound is that PN-H is anionic due to the deprotonation of the 4-(hydroxymethyl) group. The packing in both structures is governed by hydrogen bonds, and in the copper compound partial stacking of bpy's at a distance of -3.55 also adds to the stability of the system. Infrared, NMR, and ligand field spectroscopic results and magnetic measurements are interpreted in light of the structures.

Heats of reaction between aniline and formaldehyde by solution calorimetry: Reaction in neutral medium

The enthalpies of reaction between aniline and HCHO at various molar proportions under neutral conditions were determined by solution calorimetry. These measurements are new in the field of aniline and HCHO condensation polymers. The specific heats of the products formed were determined by differential scanning calorimetry and were used in the enthalpy calculations. Plots of enthalpy of reaction calculated with respect to aniline and HCHO vs. different A/F molar ratios were made. From the enthalpy data it appears that the reactions between different A/F molar ratios yield different products.

Self-assembly of a Pd-II neutral molecular rectangle via a new organometallic Pd-2(II) molecular clip and oxygen donor linker

Two components self-assembly of a Pd-4 neutral molecular rectangle driven by Pd-O bond coordination has been achieved and this pi-electron rich rectangle shows fluorescence quenching in presence of nitroaromatics, which are the chemical signatures of many explosives.

Growth of ionization currents in nitrogen

Townsend's primary and secondary ionization coefficients α/p and γ were determined in nitrogen over a wide range of E/p (100-1000 V cm−1 Torr−1) and p (0·4 to 12 Torr at 0 °C) using the pressure variation technique. This technique, along with the Gosseries method of evaluation of ionization coefficients, seems to be more suitable at higher values of E/p, since the errors in these coefficients could be minimized by a suitable selection of p and d, thus eliminating the non-equilibrium ionization condition.

Growth of ionization currents in nitrogen

Townsend's primary and secondary ionization coefficients α/p and γ were determined in nitrogen over a wide range of E/p (100-1000 V cm−1 Torr−1) and p (0·4 to 12 Torr at 0 °C) using the pressure variation technique. This technique, along with the Gosseries method of evaluation of ionization coefficients, seems to be more suitable at higher values of E/p, since the errors in these coefficients could be minimized by a suitable selection of p and d, thus eliminating the non-equilibrium ionization condition.

Charge transfer complexes of crown ethers with neutral organic gyama-acceptor, 2-dicyanoethylene 1,3-indane dione

The interaction of benzo-15-crown-5, dibenzo-18-crown-6 and dibenzo-24-crown-8 with 2-dicyanoethylene 1,3-indane dione in CH2Cl2 has been described in terms of the formation of 1 : 1 molecular complexes. The magnitude of association constants and thermodynamic parameters indicate cooperative interactions of oxygens with the acceptors. The 1H and 13C NMR spectra of the complexes show that gyama-gyama interactions are a major source of ground state stabilization in these complexes.

Electronic Structure and Bonding in Neutral and Dianionic Boradiphospholes: R ' BC2P2R2 (R=H, tBu, R '=H, Ph)

Classical and non-classical isomers of both neutral and dianionic BC2P2H3 species, which are isolobal to Cp+ and Cp-, are studied at both B3LYP/6-311++G(d,p) and G3B3 levels of theory. The global minimum structure given by B3LYP/6-311+ + G(d,p) for BC2P2H3 is based on a vinylcyclopropenyl-type structure, whereas BC2P2H32- has a planar aromatic cyclopentadienyl-ion-like structure. However, at the G3B3 level, there are three low-energy isomers for BC2P2H3: 1)tricyclopentane, 2) nido and 3) vinylcyclopropenyl-type structures, all within 1.7 kcal mol(-1) of each other. On the contrary, for the dianionic species the cyclic planar structure is still the minimum. In comparison to the isolobal Cp+ and HnCnP5-n+ isomers, BC2P2H3 shows a competition between pi-delocalised vinylcyclopropenyl- and cluster-type structures (nido and tricyclopentane). Substitution of H on C by tBu, and H on B by Ph, in BC2P2H3 increases the energy difference between the low-lying isomers, giving the lowest energy structure as a tricyclopentane type. Similar substitution in BC2P2H32- merely favours different positional isomers of the cyclic planar geometry, as observed in 1) isoelectronic neutral heterodiphospholes EtBu2C2P2 (E=S, Se, Te), 2) monoanionic heterophospholyl rings EtBu2C2P2 (E=P-, As-, Sb-) and 3) polyphospholyl rings anions tBu(5-n)C(n)P(5-n) (n=0-5). The principal factors that affect the stability of three-, four-, and five-membered ring and acyclic geometrical and positional isomers of neutral and dianionic BC2P2H3 isomers appear to be: 1) relative bond strengths, 2) availability of electrons for the empty 2p boron orbital and 3) steric effects of the tBu groups in the HBC(2)P(2)tBu(2) systems.

Investigations on voltages and currents in the lightning protection system of the Indian satellite launch pad-I during a stroke interception

A reliable protection against direct lightning hit is very essential for satellite launch pads. In view of this, suitable protection systems are generally employed. The evaluation of efficacy of the lightning protection schemes among others requires an accurate knowledge of the consequential potential rise at the struck point and the current injected into soil at the earth termination. The present work has made a detailed effort to deduce these quantities for the lightning protection scheme of the Indian satellite launch pad-I. A reduced scale model of the system with a frequency domain approach is employed for the experimental study. For further validation of the experimental approach, numerical simulations using numerical electromagnetic code-2 are also carried out on schemes involving single tower. The study results on the protection system show that the present design is quite safe with regard to top potential rise. It is shown that by connecting ground wires to the tower, its base current and, hence, the soil potential rise can be reduced. An evaluation of an alternate design philosophy involving insulated mast scheme is also made. The potential rise in that design is quantified and the possibility of a flashover to supporting tower is briefly looked into. The supporting tower is shown to have significant induced currents.

A voltage-sensorless control method to balance the input currents of a three-wire boost rectifier under unbalanced input voltages condition

This paper proposes a control method that can balance the input currents of the three-phase three-wire boost rectifier under unbalanced input voltage condition. The control objective is to operate the rectifier in the high-power-factor mode under balanced input voltage condition but to give overriding priority to the current balance function in case of unbalance in the input voltage. The control structure has been divided into two major functional blocks. The inner loop current-mode controller implements resistor emulation to achieve high-power-factor operation on each of the two orthogonal axes of the stationary reference frame. The outer control loop performs magnitude scaling and phase-shifting operations on current of one of the axes to make it balanced with the current on the other axis. The coefficients of scaling and shifting functions are determined by two closed-loop prportional-integral (PI) controllers that impose the conditions of input current balance as PI references. The control algorithm is simple and high performing. It does not require input voltage sensing and transformation of the control variables into a rotating reference frame. The simulation results on a MATLAB-SIMULINK platform validate the proposed control strategy. In implementation Texas Instrument's digital signal processor TMS320F24OF is used as the digital controller. The control algorithm for high-power-factor operation is tested on a prototype boost rectifier under nominal and unbalanced input voltage conditions.

Neutral-point balancing of neutral-point-clamped three-level inverter with a front end switched rectifier DC source for the full modulationn range

A switched rectifier DC voltage source three-level neutral-point-clamped (NPC) converter topology is proposed here to alleviate the inverter from capacitor voltage balancing in three-level drive systems. The proposed configuration requires only one DC link with a voltage of half of that needed in a conventional NPC inverter. To obtain a rated DC link voltage, the rectifier DC source is alternately connected in parallel to one of the two series capacitors using two switches and two diodes with device voltage ratings of half the total DC bus voltage. The frequency at which the voltage source is switched is independent of the inverter and will not affect its operation since the switched voltage source in this configuration balances the capacitors automatically. The proposed configuration can also be used as a conventional two-level inverter in the lower modulation index range, thereby increasing the reliability of the drivesystem. A space-vector-based PWM scheme is used to verify this proposed topology on a laboratory system.

Frequency characteristics of very fast transient currents in a 245-kV GIS

The conducted as well as the induced voltages on control cables and control circuits due to transient electromagnetic (EM) fields generated during switching operations in a gas-insulated substation (GIS) depend on the waveshape of the very fast transient overvoltages and the associated very-fast transient currents (VFTCs). The aim of this paper is to build a basis for characterizing the VFTC generated in gas-insulated switchgear and the,associated equipment during switching operations for the study of transient coupling phenomena. The peak magnitudes of VFTC and their dominant frequency content at various locations have been computed in a 245-kV GIS for different switching operations as well as substation configurations. Finally, the influence of the substation layout on the frequency spectrum, dominant frequencies, and the highest possible frequency component of the VFTC at various distances from the switch have been reported.

Growth of ionization currents in dry air at high values of E/N

Uniform field steady-state ionization currents were measured in dry air as a function of N at constant E/N (E is the electric field strength and N the gas number density) and constant electrode separation d for 14·13 × 10-16 less-than-or-eq, slant E/N less-than-or-eq, slant 282·5 × 10-16 V cm2. Uniform field sparking potentials were also measured for Nd range 1·24 × 1016 less-than-or-eq, slant Nd less-than-or-eq, slant 245 × 1016 cm-2. The ratio of the Townsend primary ionization coefficient α to N, α/N, was found to depend on E/N only. The secondary coefficients were also evaluated for aluminium and gold-plated electrodes for the above range of E/N. Measurements of the sparking potentials showed that Paschen's law is not obeyed in air at values of Nd near and below the Paschen minimum.