Volume 114, Issue 2
April 2002, pages 93-162
pp 93-105 April 2002
A new iron fluorophosphate of the composition, [C6N4H21] [Fe2F2(HPO4)3][H2PO4]·2H2O,I has been prepared by the hydrothermal route. This compound contains iron fluorophosphate layers and the H2PO4- anions are present in the interlayer space along with the protonated amine and water molecules. The compound crystallizes in the monoclinic space group P21/c.(a = 13.4422(10) Å,b = 9.7320(10) Å, c = 18.3123(3) Å, β= 92.1480°,V= 2393.92(5) Å3, Z = 4,M = 719.92,dcalc. = 1.997 g cm-3, R1 = 0.03 andwR2= 0.09).
pp 107-114 April 2002
The compound (NH4)7[ VvO4W10VIV2VIO36]·ca.22H2O (1) has been synthesized from an aqueous ammonium acetate buffer (pH 4) containing sodium vanadate, sodium rungstate_and sodium dithionite. Compound (1) crystallizes in a cubic space groupFm — 3, witha = 22.2001(6) Å and Z = 8. The anion [VvO4W10VIV2IVO36]7- is a typical Keggin type structure with VVO4 as the central tetrahedron. (1) has further been characterized by elemental analyses, redox titration, IR, EPR, and electronic spectroscopy and room temperature magnetic moment measurement.
pp 115-124 April 2002
Equilibrium and solution structural study of mixed-metal-mixed-ligand complexes of Cu(II), Ni(II) and Zn(II) with L-cysteine, L-threonine and imidazole are conducted in aqueous solution by potentiometry and spectrophotometry. Stability constants of the binary, ternary and quaternary complexes are determined at 25 ±1°C and in I= 0.1 M NaClO4. The results of these two methods are made selfconsistent, then rationalized assuming an equilibrium model including the species H3A, H2A, A, BH, B, M(OH), M(OH)2, M(A), MA(OH), M(B), M(A)(B), M2(A)2(B), M2(A)2(B-H), M1M2(A)2(B) and M1M2(A)2(B-H) (where the charges of the species have been ignored for the sake of simplicity) (A = L-cysteine, L-threonine, salicylglycine, salicylvaline and BH = imidazole). Evidence of the deprotonation of BH ligand is available at alkalinepH. N1H deprotonation of the bidentate coordinated imidazole ligand in the binuclear species atpH > 70 is evident from spectral measurements. Stability constants of binary M(A), M(B) and ternary M(A)(B) complexes follow the Irving-Williams order.
pp 125-136 April 2002
New biheterocyclic compound was synthesized as starting material to prepare new photosensitizers mono-, tri-, substituted tri-, azadimethine and mixed cyanine dyes. Absorption-structure relationship of the synthesized cyanine dyes were determined by studying their electronic spectral behaviour in ethanol. The structure of the compounds were identified by elemental analysis, IR and1HNMR spectral data.
pp 137-148 April 2002
The oxidation of 34 organic sulphides hy 2,2′-hipyridinium chlorochromate (BPCC) resulted in the formation of the corresponding sulphoxides. The reaction is first order with respect to both BPCC and the sulphide, and is catalysed by hydrogen ions. The hydrogen-ion dependence has the form:kobs = a+b[H+]. The oxidation was studied in 19 different organic solvents. An analysis of the solvent effect by Swain’s equation showed that the both cation-and anion-solvating powers of the solvents play important roles. The rates of oxidation meta- andp-substituted phenyl methyl sulphides were correlated with Charton’s LDR equation. The rates of theo-compounds showed excellent correlation with the LDRS equation. Oxidation of thep-compounds is more susceptible to the delocalizationeffect. Oxidation of themcompounds exhibited a greater dependence on the field effect. In the oxidation of theo-compounds, the contribution of delocalized effect is slightly more than that of the field effect. The oxidation of alkyl phenyl sulphides is subject to both polar and steric effects of the alkyl groups. Polar reaction constants are negative, indicating an electron-deficient sulphur centre in the rate-determining step. A mechanism involving formation of a sulphurane intermediate in the slow step has been proposed.
pp 149-154 April 2002
Rates of oxidation of dimethyl sulphoxide (DMSO) by HOBr producedin situ from sodium bromate-sodium bisulphite reagent have been studied iodometrically in aqueous medium. The order in [DMSO] is one when [DMSO] < 001 mol dm-3, fractional when [DMSO] is between 0.01 and 0.5mol dm-3 and zero when (DMSO) > 0.5 mol dm-3. Different rate laws are operative under these three conditions though HOBr is the effective oxidizing species in all the cases. A mechanism involving an intermediate four-membered cyclic transition state between DMSO and HOBr (formation constantK), which decomposes in a slow step with a rate constant(k) has been proposed. Thermodynamic parameters for the adduct formation step and activation parameters for the first-order decomposition of the adduct step have been evaluated in the temperature range 308–323 K. Activation parameters have also been determined while the orders in [DMSO] are unity and zero. The reaction product has been identified as dimethyl sulphone (DMSO2).
pp 155-162 April 2002
An attempt has heen made to investigate the effect of temperature on the conductivity of polypyrrole conducting polymer films prepared by an electrochemical method in an aqueous medium using camphor sulfonate as the dopant. The polymer was grown from aqueous solutions employing a range of temperatures (l–60°C). It was found that with increase in temperature the conductivity decreased and the optimum temperature was found to be between 10 and 30°C. The results showthatthe polymer formed at low temperature has higher conductivity and is stronger than that formed at higher temperatures. Characterization by X-ray scattering shows that interlayer distance, dBragg (Å), increases with increasing temperature. The morphology of the films formed was studied by using a scanning electron microscope (SEM). The changes in conductivity and physical appearance were interpreted as being due to compactness in the molecular packing and formation ofαβ linkages in the film.
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