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ABSTRACT: The enthalpies of solution, Delta(sol)H(m), for 5,10,15,20-tetraphenylporphine (CA registry number 917-23-7, TPP), 5,10,15,20-tetraphenylporphine of Co(II), Ni(II), Cu(II), and Zn(II) (to be written as CoTPP, NiTPP, CuTPP, and ZnTPP) in chloroform, were calorimetrically measured at T = 298 K in the concentration ranging from 3.5 x 10(-5) to 2.8 x 10(-4) mol.kg(-1). Through the linear extrapolation of the experimental data, corresponding values at infinite dilution were determined as: Delta(sol)H(m) (ZnTPP) = (55.5 +/- 0.2) kJ x mol(-1), Delta(sol)H(m) (CoTPP) = (36.9 +/- 0.2) kJ x mol(-1), Delta(sol)H(m) (TPP) = (25.7 +/- 0.6) kJ x mol(-1), Delta(sol)H(m) (NiTPP) = (15.6 +/- 0.1) kJ x mol(-1), and Delta(sol)H(m) (CuTPP) = (15.6 +/- 0.1) kJ x mol(-1). The enthalpies of solvation for the five compounds were also determined using the previously published values for the enthalpy of sublimation, as well as complementary data from the literature. The values obtained are as follows: Delta(solv)H(m)(TPP) = -(158.3 +/- 2.1) kJ x mol(-1), Delta(solv)H(m)(CoTPP) = -(154.1 +/- 2.0) kJ x mol(-1), Delta(solv)H(m)(CuTPP) = -(149.4 +/- 5.0) kJ x mol(-1) Delta(solv)H(m)(NiTPP) = -(141.4 +/- 4.0) kJ x mol(-1), and Delta(solv)H(m)(ZnTPP) = -(140.5 +/- 3.0) kJ x mol(-1). The results are analyzed in relation to several molecular properties such as ionic radius, electronic spectra, and Connolly surface. An explanation of the observed trends for solvation enthalpies is proposed.
Inorganic Chemistry 12/2009; 49(2):659-64. · 4.60 Impact Factor
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ABSTRACT: The compound, 5,10,15,20-tetrakis(4-methoxyphenyl)porphine zinc(II) (ZnTMPP), was prepared, and its thermochemical properties were experimentally established. The standard molar energy of combustion (Delta(c)U degrees m) was determined from oxygen rotating-bomb combustion calorimetry experiments. The standard molar enthalpies of combustion (Delta(c)H degrees m) and formation (Delta(f)H degrees m) were derived. The enthalpy of sublimation (Delta(cr)(g)H degrees m) was determined by Knudsen effusion at high temperatures. With these results, the standard molar enthalpies of formation and atomization (Delta(at)H degrees m) in the gas state were calculated. A summary of the results at T = 298.15 K (p degrees = 0.1 MPa) is shown in Table 1. Using these results and those previously obtained for the free ligand, 5,10,15,20-tetrakis(4-methoxyphenyl)porphine, the mean dissociation enthalpy for the Zn-N coordination bond is obtained as D(Zn-N) = (160 +/- 9) kJ.mol-1. This value is consistent with the results obtained using the same experimental approach in a similar system (5,10,15,20-tetraphenylporphine, TPP/ZnTPP) reported elsewhere. A discussion of the strength for the Zn-N coordination bond is made in terms of the structural and electronic features of the molecules involved.
Inorganic Chemistry 11/2007; 46(22):9332-6. · 4.60 Impact Factor
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ABSTRACT: The values of the molar standard enthalpies of formation, Delta(f)H(o)(m)(C(76), cr) = (2705.6 +/- 37.7) kJ x mol(-1), Delta(f)H(o)(m)(C(78), cr) = (2766.5 +/- 36.7) kJ x mol(-1), and Delta(f)H(o)(m)(C(84), cr) = (2826.6 +/- 42.6) kJ x mol(-1), were determined from the energies of combustion, measured by microcombustion calorimetry on a high-purity sample of the D(2) isomer of fullerene C(76), as well as on a mixture of the two most abundant constitutional isomers of C(78) (C(2nu)-C(78) and D(3)-C(78)) and C(84) (D(2)-C(84), and D(2d)-C(84). These values, combined with the published data on the enthalpies of sublimation of each cluster, lead to the gas-phase enthalpies of formation, Delta(f)H(o)(m)(C(76), g) = (2911.6 +/- 37.9) kJ x mol(-1); Delta(f)H(o)(m)(C(78), g) = (2979.3 +/- 37.2) kJ x mol(-1), and Delta(f)H(o)(m)(C(84), (g)) = (3051.6 +/- 43.0) kJ x mol(-1), results that were found to compare well with those reported from density functional theory calculations. Values of enthalpies of atomization, strain energies, and the average C-C bond energy were also derived for each fullerene. A decreasing trend in the gas-phase enthalpy of formation and strain energy per carbon atom as the size of the cluster increases is found. This is the first experimental evidence that these fullerenes become more stable as they become larger. The derived experimental average C-C bond energy E(C-C) = 461.04 kJ x mol(-1) for fullerenes is close to the average bond energy E(C-C) = 462.8 kJ x mol(-1) for polycyclic aromatic hydrocarbons (PAHs).
The Journal of Physical Chemistry B 09/2007; 111(30):9031-5. · 3.70 Impact Factor
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ABSTRACT: The enthalpic contribution to the anomeric effect in r-2-carboethoxy-trans-4,trans-6- and r-2-carboethoxy-cis-4,cis-6-dimethyl-1,3-dithianes was determined by reaction–solution calorimetry. The enthalpy of solution of both isomers in pure p-dioxane and the enthalpy of solution and isomerization in the same solvent and in the presence of trifluoroacetic acid were experimentally measured. From these results the corresponding enthalpies of isomerization in solution were calculated, and were found to be ΔHax→eq = −0·16 ± 0·04 kcal mol−1 (−0·67 ± 0·18 kJ mol−1) and ΔSax→eq = −2·68 ± 0·1 cal K−1 mol−1 (−11·2 ± 0·4 J K−1 mol−1). The slightly negative ΔH term nevertheless reflects a substantial anomeric effect owing to the countervailing steric effects in the axial isomer. The significant entropy loss in the equatorial isomer was explained in terms of intramolecular electrostatic effects. The results are in agreement with those obtained from NMR studies of the conformational behaviour of 2-carboethoxy-5-methyl-5-aza-1,3-dithiacyclohexane.
Journal of Physical Organic Chemistry 10/2004; 7(10):561 - 566. · 1.96 Impact Factor
