Franco Cristiani

Charge transfer complexes of benzoxazole-2(3H)-thione and benzoxazole-2(3H)-selone with diiodine: X-ray crystal structure of benzoxazole-2(3H)-thione bis(diiodine)

Abstract Solids of stoichiometry 1·I2 (C7H5I2NOS; I), 1·2I2 (C7H5I4NOS; II), 2·I2 (C7H5I2NOSe; III) and 2·2I2 (C7H5I4NOSe; IV) have been obtained by reacting respectively benzoxazole-2(3H)-thione (1) and benzoxazole-2(3H)-selone (2) with molecular diiodine in a 1:1 or 1:2 molar ratio in CH2Cl2 solution. Crystals suitable for X-ray structure determination have been obtained only for II and contain units formed by one diiodine molecule bonded almost linearly [178.44(4)°] to the thionic sulphur atom of 1 and another diiodine molecule weakly interacting with the former. The FT-Raman spectrum in the characteristics v(I-I) region shows two bands for compound II at 176 and 159 cm−1, in accordance with the presence of two differently perturbed diiodine molecules [ I (1)– I (2) = 2.769(1) A , I (3)– I (4) = 2.729(1) A ] . The FT-IR and FT-Raman spectra of compounds I, III and IV are discussed in comparison with the spectrum of II and with those reported for similar charge transfer complexes.

Copper(II) and nickel(II) uptake from aqueous solutions by cork wastes: a NMR and potentiometric study

Due to the increasing interest in the use of biomasses from agriculture as removing agents for heavy metals in waste effluents, we present here a joint potentiometric and 13C MAS and cross polarization-magic angle spinning NMR (CP-MAS NMR) study on cork interaction with Cu(II) and Ni(II). Through potentiometry we were able to distinguish two kind of interactions, a stronger one which involves protonated sites on cork and a second that allows hydroxide precipitation of the bound metal ion into the cork structure. NMR signal analysis suggests a specific metal complexation on the carbohydrate moieties of polymeric cork matrix. The 13C MAS NMR suggests that the dynamics in the MHz range and the overall arrangement of polymeric matrix is not affected by metal binding; and the spin relaxation times T1ρ(1H) and T1ρ(13C) show that no significant difference of relaxation processes in the KHz range is introduced by metal coordination.

A POTENTIOMETRIC, SPECTROPHOTOMETRIC AND 1H NMR STUDY ON THE INTERACTION OF CIMETIDINE, FAMOTIDINE AND RANITIDINE WITH PLATINUM(II) AND PALLADIUM(II) METAL IONS

Abstract Spectrophotometric, potentiometric and 1H NMR results on the M-L systems [M = PdII or PtII and L = cimetidine, famotidine or ranitidine] are clearly indicative of the strong chelating ability of these antiulcerative drugs towares metal ions. In view of the great biological interest in these two metals, their coordination to such drugs should have significant implications.

Characterization of the ionization and spectral properties of sulfonephthalein indicators. Correlation with substituent effects and structural features.

The pK values of the second ionization of a set of substituted sulfonephthaleins are studied by spectrophotometry and (13)C NMR spectroscopy. A study of the correlation between equilibrium and spectral data on the one hand and the substituent effects on the other is presented, using the dual substituent analysis of Swain and Lupton. This shows a complete dependence of pK values on the F field variable, and of the wavelengths of the bands of basic forms on the R resonance variable.

REACTIVITY OF 1,3,5-TRITHIACYCLOHEXANE AND 1,3,5-TRISELENACYCLOHEXANE TOWARDS MOLECULAR DIIODINE. CRYSTAL STRUCTURES OF THE DIIODINE ADDUCTS

Abstract The reactions between I2 and the donors (D) 1,3,5-trithiacyclohexane (1) and 1,3,5-triselenacyclohexane (2), in methylene chloride and hot benzene respectively (1:1 I2:D molar ratio) give the solid adducts 1·I2 (I) and 2 · I2 (II) whose structures have been solved by X-ray diffraction. The use of an excess of diiodine up to the molar ratio 2:1 always gives II from 2, and 1·2I2 (III) from 1. Compound I consists of polymeric chains in which each diiodine bridges between different 1 molecules, while II consists of discrete molecular units. The Raman ν(II) frequency and II bond distance in I fits well with the previously found linear correlation. This correlation suggests two different II bond distances for III. The comparison of the FTIR and FT-Raman spectra for II is consistent with the three-body model for SeII. The association constant between 1 and I2 in methylene chloride has been also studied both by UV-visible and 13C NMR spectroscopy, giving K values at 21°C in good agreement.

Characterization of the ionization and spectral properties of mercapto-carboxylic acids Correlation with substituents and structural features.

The ionization constants in aqueous solutions of meso- and dl-dimercaptosuccinic acid and of monomethyl and dimethyl meso-succinates were carefully determined by potentiometric and spectrophotometric methods as a result of the increasing interest in these molecules as heavy metal chelators. In order to explain the influence of various substituents on ionization and (13)C NMR properties, the study was extended to the related oxygen derivatives of succinic acid and to simpler ethanoic derivatives. With the Swain-Lupton dual substituent treatment it was possible to clarify the influence of substituents on both spectral and equilibrium parameters. The differences in pK due to conformation are also discussed.

NH stretching vibrations of 5,5-dimethylimidazolidines with O,S or Se at C-2 and C-4☆

Abstract The i.r. spectra of the title compounds have been recorded in the region 3500-3150 cm −1 in CH 2 Cl 2 and CH 2 Cl 2 /DMSO solutions. In the region of the free NH stretching vibrations, the spectra show an envelope of bands which have been deconvoluted in order to separate the two ν (NH) contributions. The peak due to ν (NH) of N-3 decreases on increasing the DMSO concentration, thus indicating that this hydrogen is mainly involved in the interaction with DMSO in accordance with its higher acidity. The influence of the exo-chalcogen atoms on these frequencies has been discussed. A good empirical correlation has been found between the ν (NH)s and the charge densities (calculated by CNDO/S) on the hydrogen and nitrogen atoms.

HYDANTOIN DERIVATIVES. SYNTHESES AND INFRARED SPECTRA OF 5,5-DIMETHYLIMIDAZOLIDINES HAVING O, S OR SE ATOMS AT C-2 AND C-4

Abstract The syntheses of a complete series of 5,5-dimethylimidazolidines 2,4-disubstituted with chalcogen atoms (O, S and Se) are reported. Their infrared spectra (4000–250 cm−1) are discussed on the basis of the selenation effect and the bands arising from [sbnd]HN[sbnd]CX[sbnd]NH[sbnd]CY[sbnd] (X, Y=O, S, Se) groups are tentatively assigned.

Zinc(II), cadmium(II) and mercury(II) halide pyrrolidine-2-thione complexes

SummaryWhite crystalline complexes of general formula ML2X2, where M = Zn, Cd, Hg; X = Cl, 13r, I and L = pyrrolidine-2-thione, were prepared and studied by i.r. spectroscopy in the 4000-200 cm−1 range. Evidence for coordination of the ligand to the metal through sulphur was found in each case. The previous assignment of the band present in the ligand at 1110 cm−1 to theν(CS) fundamental is discussed.

An 1H NMR and potentiometric study of the interaction between platinum(II) and cimetidine

Abstract The platinum(II)-cimetidine system was studied in aqueous solutions by potentiometric and 1H NMR methods. Evidence is given of the formation of 1:1 and 1:2 platinum(II)-ligand complexes, with different degrees of protonation. A bonding scheme is proposed on the basis of NMR spectra.