Publications

Abstract The standard (po = 0.1 MPa) molar enthalpy of formation, at the temperature 298.15 K, of crystalline bis(2,2,6,6-tetramethylheptane-3,5-dionato) dioxouranium(VI) {uranyl(VI) dipivaloylmethanate, UO2(DPM)2}, was determined by solution-reaction calorimetry as -(2169.9±7.6) kJ·mol-1. The vapour pressure of the crystal, as function of the temperature, was measured using the Knudsen mass-loss effusion technique and the standard molar enthalpy of sublimation, at the temperature 298.15 K, was derived as (156.9±1.9) kJ·mol-1. From these results, the standard molar enthalpy of formation of the complex, in the gaseous state, was derived and the mean uranium(VI)-oxygen bond-dissociation enthalpy for the binding of the ligand to the metal, 〈D〉(U-O), was calculated as (223±10) kJ·mol-1.

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion at the temperature T = 298.15 K were measured by static-bomb calorimetry for crystalline 2,2′,4,4′,6,6′-hexamethylazobenzene-N,N-dioxide (HHMABOO), 2,2′,6,6′-tetramethylazobenzene-N,N-dioxide (TMABOO), 2,4,6-trimethylnitrobenzene (NITME), and liquid 2,6-dimethylnitrobenzene (NITXY). The enthalpies of sublimation at the temperature 298.15 K of HMABOO and TMABOO were assessed from vapour-pressure measurements; the enthalpy of sublimation of NITME and the enthalpy of vaporization of NITXY were measured by microcalorimetry. The standard molar enthalpies of decomposition of the crystalline N,N -dioxides to the corresponding gaseous monomeric nitroso-compounds at T = 298.15 K were measured by microcalorimetry: for HMABOO, (181.1±2.5) kJ·mol-1, and for TMABOO, (179.2±2.2) kJ·mol-1. For HMABOO and TMABOO, D (N=N)/(kJ·mol-1) was derived as (74.1±12.2) and (72.2±12.2), and 〈D(N-O>〉/(kJ·mol-1) as (285.7±6.8) and (287.8±6.6), respectively. D (N-O)/(kJ·mol-1) in NITME and in NITXY was derived as (383.4±2.9) and (380.4±2.3), respectively.

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion at the temperature 298.15 K were measured by static-bomb calorimetry for p -azoxyanisole and p-azoxyphenetole, and the standard molar enthalpies of sublimation of the temperature 298.15 K were measured by microcalorimetry. [[formula]] From the standard the molar enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies of the N-O bonds were derived: D (N-O)/(kJ·mol-1): p-azoxyanisole, 317.2±5.7; p-azoxyphenetole, 320.4±4.9. Microcalorimetric measurements were made to derive the molar enthalpies of the transitions: crystal-to-liquid: for p-azoxyanisole, (29.3±0.8) kJ·mol-1, (1.0±0.5) kJ·mol-1; and for p-azoxyphenetole, (27.0±0.8) kJ·mol-1, (1.7±0.6) kJ·mol-1, respectively.

Abstract The variations observed in synchronous fluorescence spectra of fulvic acids have been characterised by principal component analysis and evolving factor analysis. Fulvic acids from coastal marine waters (mfua) were examined as a function of pH (between 2 and 7) and Cu(II) concentration. Fulvic acids from soil (sfua) were examined as a function of pH (between 2 and 7) and Cu(II), Co(II) and Ni(II) concentration. Fluorescence properties of sfua are characterised by a constant plus three varying components (defined by three individual spectra), corresponding to three acid-base equilibria with pK(a) values of 3.0, 4.6 and 6.4. For mfua, a constant plus two varying components (defined by three individual spectra) were detected, corresponding to two acid-base equilibria with pK(a) values of 3.1 and 5.3. The influence of the ions on the acid-base equilibrium diagrams is also quantified.

Abstract The standard (p-degrees = 0.1 M Pa) molar enthalpies of formation at 298.15 K in the gaseous state of some beta-ketoimines, RCOCH=C(CH3)NHR1, were determined from their enthalpies of combustion and of sublimation, DELTA(f)H(m)degrees(g)/kJ mol-1: R=CH3, {R1 = C6H5, -66.0 +/- 4.2; R1 = p-C6H4NO2, -98.9 +/- 5.0}: R = C6H5, {R1 = H, -48.7 +/- 3.5; R1 = CH3, -53.7 +/- 4.7; R1 = C6H5, 69.1 +/- 4.2). From these results it is shown that the increase in delocalization energy from R = CH3 to R = C6H5 matches the corresponding increase between acetylacetone and benzoylacetone. Crystal structures are reported for R = CH3, R1 = p-C6H4NO2, and R = C6H5 {R1 = H, R1 = CH3}, and show that those beta-ketoimines with R = C6H5 have a more delocalized structure in the -COCH=C(CH3)NH-moiety than those with R = CH3 in accord with the thermochemical results.

Abstract Partial molar heat capacities at infinite dilution, C(p,2)infinity, have been determined calorimetrically for D-mannitol and D-sorbitol in water, dimethyl sulfoxide and formamide, at 298.15 K. The C(p,2)infinity values obtained, which are similar for the three solvents, are much higher than the heat capacities for the pure compounds. The large DELTAC(p)infinity values for the dissolution process are believed to be partly due to the existence of several rotamers in solution. Sorbitol seems to be more sensitive than mannitol to specific solvent effects.

Abstract Potentials of zero charge, E(sigma=0), and the temperature coefficients of E(sigma=0) for stepped surfaces of sold single crystals (511), (533), (331) and (311) were obtained from the minimum of the differential capacity curve in dilute HClO4 solutions. The results are compared with those obtained for the low index faces and dilute in terms of the effect of the surface density of steps and the step orientation. The possible relevance of the effect of steps on the interaction of water with gold surfaces is discussed.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressure as a function of temperature for six halogen-substituted 8-hydroxyquinolines. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation Δg crHo m(Tm), at the mean temperature Tm of the experimental temperature range were derived, and the standard molar enthalpies of sublimation at T = 298.15 K were calculated. {A figure is presented}. The results obtained in this work together with the previously reported ones for other hydroxyquinolines, allowed us to find the correlation: Δcr g Hm o (T0.5 Pa) / (kJ {dot operator} mol- 1) = 0.313 (T0.5 Pa / K) - 3.68,. where T0.5 Pa is the temperature at which the equilibrium vapour pressure of each substance is 0.5 Pa.