S. Nunziante Cesaro

Thermodynamic study of the vaporization of uracil

Abstract The vapour pressure of uracil was measured in the temperature range 452–587 K using different techniques and the pressure—temperature equation log P (kPa) = 12.13 ± 0.50 — (6823 ± 210)/ T was derived. The thermodynamic functions of gaseous and solid uracil were also evaluated through spectroscopic and calorimetric measurements. The sublimation enthalpy of uracil, Δ H 0 298 = 131 ± 5 kJ mole −1 , was derived from second and third law treatment of the vapour data.

Matrix and ab initio infrared spectra of thiourea and thiourea-d4

Abstract The FTIR spectrum of thiourea and thiourea-d 4 isolated in argon and nitrogen matrices are presented for the first time and discussed in terms of normal modes predicted by ab initio calculations. Vibrational frequencies, IR intensities and isotopic shifts obtained from the density functional B3-LYP/6-31+G(2d,p) calculations show the most satisfactory agreement with experiments. In contrast with previous results, the present theoretical study indicates non-planarity of the molecule. The lowest energy structure has C 2 symmetry and the less stable isomers has C s symmetry. Experimental data clearly indicate the presence of a single isomer in the vapor. The decomposition of thiourea for vaporization temperature over 410 K is also discussed.

Coordination compounds of biological interest: thermal properties of some compounds of saccharin (o-benzoic sulfimide) with divalent metal ions

The thermal properties of cobalt(II) and copper(II) complexes of saccharin (sacc) (o-benzoic sulfimide) have been studied, and are compared with those of ternary complexes of cobalt(II) and copper(II) having both saccharin and pyridine as ligands. The thermal behaviour is discussed in terms of the bonds between the central ion and the ligands. The frequency shifts of the carbonyl and sulfonyl groups support the hypotheses derived from the thermal data. The thermal stability scale CO(II) /s> Cu(II) is always obtained while the stability constant scale is CO(II) < Cu(II).

FTIR matrix isolation study on gaseous calcium dihalide molecules

Abstract FTIR measurements were carried out on matrix-isolated calcium dihalide vapours. CaF 2 , CaCl 2 , CaBr 2 and CaI 2 samples were vaporized at temperatures ranging from 1100 K to 1700 K and the vapours were trapped in argon and krypton matrices. Bands of monomers, dimers and in one case of a more complex aggregate were observed. The spectra were interpreted on the basis of polarizable ion model calculations. Regarding the structure of the dimer molecule, D 2h symmetry was established from the experimental measurements and theoretical results. A trimer molecule was found for CaF 2 and a D 2d symmetry structure is suggested for it.

Stabilization of Carbonate Hydroxyapatite by Isomorphic Substitutions of Sodium for Calcium

Carbonate hydroxyapatite (CHA) is an analogue of the mineral component of bone tissue. Synthetic CHA is thermally unstable: it readily decomposes with carbon oxide evolution when sintered to ceramics. Its thermal stability has been studied as affected by partial isomorphic substitution of sodium for calcium intended to compensate a possible charge imbalance induced by CO32− groups. Investigative tools were thermogravimetry and FTIR spectroscopy of the condensed vapor produced by heating CHA samples doped with 0.4 and 0.8 wt % sodium. Sodium does not improve the thermal stability of CHA: weight loss on heating increases with increasing sodium level; evolution of carbon oxides occurs at lower temperatures and more intensively. Sodium enhances the generation of B-type defects (CO32− → PO43− substitutions); these defects are thermodynamically less stable than AB-type defects (2CO32− → PO43−, OH− substitutions), which are characteristic of sodium-free CHA.

Infrared matrix isolation of, and bonding in, the oxides of group vib elements: O3, SO2, SeO2, and TeO2

Abstract Vibrational frequencies, force constants and geometrical parameters of the oxides of group VIB elements in rare gas matrices are compared with those in the gas phase. Bonding in these species is discussed.

Effects of intermolecular hydrogen bonding on the molecular structure and vibrational spectrum of diacetamide

Abstract Structures, vibrational spectra and methyl rotational barriers of diacetamide, CH 3 CONHCOCH 3 , and of hydrogen-bonded dimers have been determined by ab initio methods. The HF/4–31G * geometry of the isolated molecule reveals a planar configuration of the amide groups and a tendency of the CH 3 group to eclipse the CO bond; MP2/6–31G * //HF/4–31G * calculations indicate the E, Z configuration of diacetamide as the most stable isomer. The structural changes induced by dimerization of E,Z -diacetamide have been determined at the HF/6–31G level for two CO⋯HN hydrogen-bonding models and are more remarkable for the cyclic than for the open structure dimer. Hydrogen bonding effects on the vibrational spectrum of diacetamide have been investigated by comparing monomer and dimer IR spectra. The Fourier transform infrared (FT-IR) spectra of diacetamide and of the N-deuterated species, CH 3 CONDCOCH 3 , measured in Ar and N 2 low-temperature matrices, have been assigned on the basis of HF/4–31G * calculations. The vibrational spectrum of the monomer has been compared with the IR spectra of concentrated matrices, where CH 3 CONHCOCH 3 undergoes appreciable self association by CO⋯HN hydrogen bonds to form structurally disordered dimers, and with the IR crystal spectra, where the strongest association gives rise to well defined cyclic dimers.

Vibrational spectra of cyclopentadienyl chlorides of titanium, zirconium and hafnium. internal rotation and thermodynamic functions

Abstract The infrared and Raman spectra of some cyclopentadienyl compounds of the transition metals, namely Ti(C5H5)Cl3 and M(C5H5)2Cl2 (M = Ti, Zr and Hf), are reported and discussed. The infrared spectra of the gaseous species isolated in argon matrices at 10 K provide structural information about the single molecules. Particular attention has been paid to the low-frequency region in order to achieve more reliable assignments for the internal-rotation modes. The structural data and the fundamental frequencies derived from the spectra are employed in a calculation of the thermodynamic functions for these compounds in the ideal gas state.

Experimental and computational study of the new gaseous molecules OMnF and OMnF2

The new gaseous species OMnF and OMnF2 were identified and studied by high-temperature Knudsen Cell Mass Spectrometry. Their thermochemical atomization energies were derived through the study of several all-gas equilibria in the temperature range 1735–1913 K. FTIR matrix isolation experiments together with ab initio and density functional calculations were performed to determine the molecular parameters, bond distances, and vibrational frequencies of OMnF(g) and OMnF2(g). The results allowed us to evaluate a set of thermal functions for the new species that were used in the evaluation of the equilibrium data. The proposed atomization energies and enthalpies of formation are ΔaH0∘(OMnF,g)=(903±5) kJ mol−1, ΔfH298.15∘(OMnF,g)=(−297±5)kJ mol−1, and ΔaH0∘(OMnF2,g)=(1470±70) kJ mol−1, ΔfH298.15∘(OMnF2,g)=(−789±70)kJ mol−1.

Far IR and Raman spectra of some gaseous titanium, zirconium and hafnium cyclopentadienyl chlorides

Abstract The far IR and Raman spectra of gaseous (C5H5)TiCl3 and (C5H5)2MCl2 species (M = Ti, Zr and Hf) are reported. The results are compared to the previous vibrational analysis of the corresponding species in the solid and matrix isolated phases. The assignment of the metal skeletal vibrations is reexamined in further detail on the basis of the new spectroscopic measurements. The torsional frequencies and the related potential barriers are investigated.