Reactivity of the tetrathiomolybdate(VI) anion towards hard and soft base chelating agents

Summary The interaction of hard base chelating agents (LH) such as 8-quinolinol (oxH), salicylaldehyde (salH) andN-nitrosophenylhydroxylamine (NphaH) with ammonium tetrathiomolybdate(VI), (1), in aqueous solution yields disulphidomolybdenum(VI) complexes, [MoS₂L₂]. The i.r. absorptions at 540 and 510 cm^–1 are assigned tov(Mo-S), which indicate that the two sulphido-groups arecis to each other, The interaction of (1) with soft base chelating agents (SS), such as dithiocarbamates (dtc), dithiophosphate (dtp) and xanthates (xan) yields dimeric sulphido-bridged sulphidomolybdenum(V) complexes, [Mo₂S₄(SS)₂] and with potassium ethylthioxanthate (KEttxan) yields a molybdenum(IV) complex, [Mo(Ettxan)₄]. The [Mo₂S₄(R₂dtc)₂] complexes were also obtained by the interaction of [MoO₂(R₂dtc)₂] with phosphorus pentasulphide in xylene. It was concluded that tetrathiomolybdate(VI) undergoes facile reduction when compared with tetraoxomolybdate(VI).     

Resonances and chaos in the collinear collision system (He,H 2 + ) and its isotopic variants

The collinear atom-diatom collision system provides one of the simplest instances of chaotic or irregular scattering. Classically, irregular scattering is manifest in the sensitive dependence of post-collision variables on initial conditions, and quantally, in the appearance of a dense spectrum of dynamical resonances. We examine the influence of kinematic factors on such dynamical resonances in collinear (He, H ₂ ⁺ ) collisions by computing the transition state spectra for collinear (He, HD⁺) and (He, DH⁺) collisions using the time-dependent quantum mechanical approach. The nearest neighbor spacing distributionP(s) and the spectral rigidity Δ₃(L) for these resonances suggest that the dynamics is predominantlyirregular for collinear (He, HD⁺) and predominantlyregular for collinear (He, DH⁺). These findings are reinforced by a significantly larger “correlation hole” in ensemble averaged survival probability ≪P(t)≫ values for collinear (He, HD⁺) than for collinear (He,DH⁺). In addition we have also examined measures of classical chaos through the dependence of the final vibrational action,n _f, on the initial vibrational phaseφ _i of the diatom, and Poincaré surfaces-of-section. They show that (He, HD⁺) collisions are partly chaotic over the entire energy range (0–2.78 eV) while (He, DH⁺) collisions, in contrast, are highly regular at collision energies below the classical threshold for reaction. Above the threshold, the scattering remains regular for initial vibrational statesv=0 and 1 of DH⁺.     

Ultrafast intermolecular hydrogen bond dynamics in the excited state of fluorenone

Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time domain have been used to investigate the dynamics of hydrogen bond in the excited singlet (S(1)) state of fluorenone in alcoholic solvents. A comparison of the features of the steady-state fluorescence spectra of fluorenone in various kinds of media demonstrates that two spectroscopically distinct forms of fluorenone in the S(1) state, namely the non-hydrogen-bonded (or free) molecule as well as the hydrogen-bonded complex, are responsible for the dual-fluorescence behavior of fluorenone in solutions of normal alcoholic solvents at room temperature (298 K). However, in 2,2,2-trifluoroethanol (TFE), a strong hydrogen bond donating solvent, emission from only the hydrogen-bonded complex is observed. Significant differences have also been observed in the temporal evolution of the absorption spectroscopic properties of the S(1) state of fluorenone in protic and aprotic solvents following photoexcitation using 400 nm laser pulses. An ultrafast component representing the solvent-induced vibrational energy relaxation (VER) process has been associated with the dynamics of the S(1) state of fluorenone in all kinds of solvents. However, in protic solvents, in addition to the VER process, further evolution of the spectroscopic and dynamical properties of the S(1) state have been observed because of repositioning of the hydrogen bonds around the carbonyl group. In normal alcohols, two different kinds of hydrogen-bonded complex of the fluorenone-alcohol system with different orientations of the hydrogen bond with respect to the carbonyl group and the molecular plane of fluorenone have been predicted. On the other hand, in TFE, formation of only one kind of hydrogen-bonded complex has been observed. These observations have been supported by theoretical calculations of the geometries of the hydrogen-bonded complexes in the ground and the excited states of fluorenone. Linear correlation between the lifetimes of the equilibration process occurring because of repositioning of the hydrogen bonds and Debye or longitudinal relaxation times of the normal alcoholic solvents establish the fact that, in weakly hydrogen bond donating solvents, the hydrogen bond dynamics can be described as merely a solvation process. Whereas, in TFE, hydrogen bond dynamics is better described by a process of conversion between two distinct excited states, namely, the non-hydrogen-bonded form and the hydrogen-bonded complex.     

Friedlander synthesis of highly functionalized isoxazolyl quinoline libraries via addition of C(sp3)–H bond to aldehydes

A novel protocol for ionic liquid (IL)-mediated C(sp³)–H bond functionalization of 3,5-dimethyl-4-nitroisoxazoles 4 to substituted o-amino benzaldehydes 5 was developed in excellent yields. Isoxazolyl aryl ethanones 7 have been synthesized from isoxazolyl aryl ethanol synthon 6. Furthermore, utilizing the later as synthons for IL promoted Friedlander synthesis of highly functionalized isoxazole substituted quinoline libraries 9. The merit of this synthesis is easily available and economical starting materials, effective utilization of all the reactants, and simple workup procedure. It is noteworthy that ionic liquid used in C(sp³)–H bond functionalization and Friedlander synthesis reactions can be recycled and reused five times without significant decrease in activity.     

Estimation of fluorine in microgramme quantities a modified procedure

A procedure is described for the estimation of fluorine in microgramme quantities by the steam-distillation of the samples with sulphuric or phosphoric acid. Traces of the acid carried over are precipitated from the distillate as silver or barium salts, in order to eliminate their interference in the subsequent titration of fluorine. The results obtained compare favourably with those of the conventional perchloric acid method. By avoiding the latter, the present method offers the advantage of both safety and simplicity.     

Exchange interactions in bis(diethyldithiocarbamato)copper(II), Cu(detc)2

The exchange coupling constant J in bis(diethyldithiocarbamato)copper(II) has been derived through analysis of the EPR g values and linewidth as a function of orientation, frequency and temperature. The single line in the ac* plane is due to the averaging of the fine-structure splitting by interdimer exchange for which a lower limit of 0.02 cm^?1 has been obtained. Analysis of the spectra in the bc plane gives an estimate of 0.008 cm^?1 for the intersite exchange.     

A reinvestigation of the reaction between titanium(iv) and salicylic acid in concentrated sulphuric acid

It is shown that the coloured species formed between TiO(2+) and salicylic acid in concentrated sulphuric acid may be a pi-complex rather than a chelate. Similar species are formed by other hydroxybenzoic acids where chelating sites for TiO(2+) are not available. The ultraviolet and NMR spectral characteristics of hydroxybenzoic acids in water, concentrated sulphuric acid and deuterochloroform are presented as evidence for the pi-complex formation. The reaction of VO(2+) with salicylic acid in concentrated sulphuric acid is shown to be due to increasing electron-donation in the pi-component of the V-O bond of VO(H(2)O)(5)(2+) as the concentration of sulphuric acid is increased, and not to the presence of salicylic acid.     

Radiation-induced copolymerization of hydrophilic monomers with vinyl acetate: Synthesis and thermal properties

Radiation-induced copolymerization of hydrophili+ monomers, viz., 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA), and N-vinyl-2-pyrrolidone (NVP) with vinyl acetate (VAc) was carried out in bulk at 25°C. The copolymer composition was determined from the acetoxy content. The copolymerization parameters were determined by a graphical method and compared with those determined by the Yezrielev, Brokhina, and Roskin (YBR) method. Thermal properties of copolymers were studied by GC-MS. Probable mechanisms were suggested from the products obtained.     

Synthesis of binaphthols over mesoporous molecular sieves

Mesoporous aluminosilicates (Al-containing NaMCM-41) were applied as catalyst supports for oxidative coupling of β-naphthol and substituted β-naphthols due to their remarkable features such as surface area, ordered mesopores and high thermal stability. The NaMCM-41 supported copper catalysts prepared by impregnation method, and Cu-NaMCM-41 was prepared by incorporating copper during synthesis. Oxidative coupling of β-naphthol reaction was studied using molecular oxygen as oxidant. The copper supported NaMCM-41 catalysts were prepared with different Si/Al ratios and calcined from 120 to 420 °C were observed to show varied product selectivity. The NaMCM-41 supported copper catalysts and Cu-NaMCM-41 were more active than the corresponding Cu/Fe supported on NaY zeolite. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), UV–DRS, ICPMS and BET surface area techniques and the reaction products were confirmed by ¹H-NMR, FTIR and HRMS. An attempt has been made to explain the product selectivity of the catalysts discussed with the above techniques. The high dispersion of Cu⁺² species observed in the catalysts having high Si/Al ratios in NaMCM-41 support and catalysts that are calcined at low temperatures, i.e. less than 420 °C, yielded an unexpected product perylene diol. A comparatively low dispersion of Cu⁺² species, noticed in catalysts having low Si/Al ratios and calcined at high temperatures, yielded binapthol as the coupled product. The effect of the variation of catalyst and the solvent are also studied.     

Kinetics of dissociation of tris-1,10-phenanthroline-iron(II) complex cation in aqueous acetic acid solutions

The reaction under study is first order in the complex ion over the entire composition range of the mixed solvent. A minimum amount of mineral acid is needed for completion of the reaction (formation of colorless products), but the rate is practically acid-independent. The influence of solvent composition and some common ions on the reaction rate have been examined. A reaction mechanism consistent with the rate behavior is proposed where water is shown as an active participant in the dissociation process. A plausible explanation for the retardation effect of HSO₄ ⁻ as against the accelerating effect of Cl⁻ under water-scarce conditions is provided.