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A computational investigation about the Lewis acid-base adducts between bases [Cp.sub.2]M[H.sub.2] (M = Mo, W) and acids B[X.sub.3] (X = F, Cl) and [Al([CH.sub.3].sub.3] is presented. Density functional methods based on pure and hybrid correlation-exchange functionals and relativistic corrections based on the zero order relativistic approximation (ZORA) have been applied. A comparison with experimental data has been addressed to give insights about the nature of the acid-base interaction with the aim to evaluate the role of the transition metal in charge donation toward the acid centre. In this respect, the likelihood of proposed criteria for recognizing the presence of transition-metal direct charge donation has been discussed. Key words: metallocenes, Lewis basicity, density functional theory (DFT), atoms in molecules (AIM), zero order relativistic approximation (ZORA). On a effectue une etude theorique des adduits acide-base de Lewis entre les bases [Cp.sub.2]M[H.sub.2] (M = Mo, W) et les acides B[X.sub.3] (X = F, Cl) et [Al([CH.sub.3].sub.3]. On a utilise les methodes de la fonctionnelle de la densite en faisant appel a des fonctionnelles de correlation-echange pures ainsi qu'hybrides et on a applique des corrections relativistes basees sur l'approximation relativiste d'ordre zero (AROZ). Une comparaison avec les donnees experimentales a ete realisee afin d'obtenir des informations sur la nature de l'interaction acide-base qui permettraient d'evaluer le role du metal de transition dans le transfert de charge vers le centre acide. Dans cette optique, on discute du potentiel d'utilite des criteres proposes pour reconnay tre la presence d'un transfert de charge direct de la part du metal de transition. Mots-cles : metallocenes, basicite de Lewis, theorie de la fonctionnelle de la densite (TFD), atomes dans une molecule << AIM >>, approximation relativiste d'ordre zero (AROZ). [Traduit par la Redaction], Introduction The acid-base adduct between bis(cyclopentadienyl)dihydridotungsten ([Cp.sub.2]W[H.sub.2]) and B[F.sub.3] was firstly communicated by Shriver (1) in 1963. It represented one of the first (and representative) examples of Lewis base behaviour [...]

The synthesis and the full spectroscopic characterization (FT-IR, FT- Raman, [sup.31]P CP MAS NMR) of trans-bis[O-ethyl-phenylphosphonodithioato][Ni.sup.II] (3) are reported. On the basis of hybrid-Density Functional Theory (DFT) calculations and Extended Huckel Theory (EHT) calculations, performed on the simpler trans-bis[O-methyl-phenylphosphonodithioato][Ni.sup.II] (2) model complex, the electronic structures of phosphonodithioato complexes in their ground states are fully described, and in particular the vibrational features are deeply analyzed, allowing an unprecedented insight into the vibrational features of trans-bis-O-methyl-phenylphosphono- and trans-bis(isopropylamidophosphono)-dithioato complexes of nickel(II), palladium(II), and platinum(II). Key words: phosphonodithioato complexes, IR, Raman, DFT calculation.

The syntheses of the first examples of selenoparabanic acid derivatives (dialkylimidazolidine-2-selone-4,5-dione, [3e.sup.R], R = Me, Et, Bu) are presented along with the X-ray crystal structure determination of 3[e.sup.Et]. To gain an insight in the properties of parabanic acid derivatives on the basis of their electronic structures, we report the results of comparative hybrid-DFT calculations performed on parabanic, thioparabanic, and selenoparabanic acids ([3a.sup.H], [3b.sup.H], and [3e.sup.H] and on their N,N'-dimethyl derivatives [3a.sup.Me], [3b.sup.Me], and [3e.sup.Me]. Calculations show that the different nature of the frontier orbitals of [3a.sup.R] compared to those of [3b.sup.R] and [3e.sup.R], might account for the different reactivities of these compounds. Moreover, the weak donor character of [3b.sup.R] and [3e.sup.R] towards molecular di-iodine, estimated by FT-Raman measurements is in agreement with the calculated NBO-charge distribution. Key words: selenation, selenoparabanic derivatives, crystal structure, DFT calculations.

The form of 8-hydroxyquinoline in different solvents is examined by using spectroscopic and computational methods. The results have shown that 8-hydroxyquinoline has displayed a clear preference for the cis conformation, but a small fraction of the trans conformation is present in water solutions.

The synthesis, characterization and photoreactivity of a series of new heteroaryl imines form the coupling between 2-benzothienyldiphenylmethyliminophosphorane and heterocyclic aldehydes are described. The reaction at 60 degree Celsius gave the formation of only the trans isomer while at high temperature cis isomer was obtained and only the cis isomers showed a photochemical reactivity to give corresponding condensed pyridine derivative.

Nonrelativistic and relativistic time-dependent density functional calculations are performed on the excited states of the [M(H2timdt)(sub 2)] (M = Ni, Pd, Pt) compounds. In all members of the series, the excited state at the lowest energy corresponds to a HOMO -> LUMO excitation and indicates that a large number of the transitions have an intraligand character.

Research has been conducted on 2,3-epoxy alcohols. The authors describe their study of the role of metal ions in regioselective opening of these alcohols carried out via hybrid density functional theory method.

Density functional theory and time-dependent density functional theory were applied to describe the ground and excited states and the spectral characteristics of the meridianal and facial isomers of aluminum tris(quinolin-8-oclate) (Alq3). Experimental meridinal Alq3 absorption band locations were well reproduced by the computations, which allowed easy assignment of the absorption bands.

Density functional theory (DFT) calculations on the geometry and bonding energy of the X - - - I intermolecular interaction of CF3I and (CH3)(sub n)X and (CH3)(sub n)XO are reported. All the adducts with the oxides as donors show a weaker interaction with CF3I than the relative donor without oxygen except the CF3I - - - ON(CH3) adduct, which has a stronger interaction.

A computational investigation about the Lewis acid–base adducts between bases Cp2MH2 (M = Mo, W) and acids BX3 (X = F, Cl) and Al(CH3)3 is presented. Density functional methods based on pure and hybrid correlation-exchange functionals and relativistic corrections based on the zero order relativistic approximation (ZORA) have been applied. A comparison with experimental data has been addressed to give insights about the nature of the acid–base interaction with the aim to evaluate the role of the transition metal in charge donation toward the acid centre. In this respect, the likelihood of proposed criteria for recognizing the presence of transition-metal direct charge donation has been discussed. [ABSTRACT FROM AUTHOR]

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The synthesis and the full spectroscopic characterization (FT-IR, FT-Raman, [sup 31] P CP MAS NMR) of trans-bis[O-ethyl-phenylphosphonodithioato]Ni[sup II] (3) are reported. On the basis of hybrid-Density Functional Theory (DFT) calculations and Extended Hückel Theory (EHT) calculations, performed on the simpler trans-bis[O-methyl-phenyl phos phono dithioato]Ni[sup II] (2) model complex, the electronic structures of phosphonodithioato complexes in their ground states are fully described, and in particular the vibrational features are deeply analyzed, allowing an unprecedented insight into the vibrational features of trans-bis-O-methyl-phenylphosphono- and trans-bis(isopropylamidophosphono)-dithioato complexes of nickel(II), palladium(II), and platinum(II).Key words: phosphonodithioato complexes, IR, Raman, DFT calculation.On rapporte la synthèse et la caractérisation spectroscopique complète (FT-IR, FT-Raman, [sup 31] P CP MAS RMN) du trans-bis[O-éthyl-phénylphosphonodithioato]Ni[sup II] (3). Sur la base de calculs de densité fonctionnelle hybride (DFT) et de calculs de Hückel étendus effectués (EHT) sur le complexe modèle plus simple, trans-bis-[O-méthyl-phénylphosphonodithioato]Ni[sup II] (2), on présente une description complète des structures électroniques des complexes phosphonodithioato dans leurs états fondamentaux et, en particulier, on a analysé en détail les caractéristiques vibrationnelles ce qui permet d'obtenir une vue sans précédent des caractéristiques vibrationnelles des complexes trans-bis-O-méthyl-phénylphosphono- et trans-bis(isopropylamidophosphono)-dithioato du nickel(II), du palladium(II) et du platine(II).Mots clés : complexes phosphonodithioato, IR, Raman, calculs DFT.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]