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Three series of phosphine chalcogenide complexes of the antimony(III) halides Sb[X.sub.3] (X = F, Cl, Br, or I) have been synthesized and characterized by spectroscopic and crystallographic methods. Complexes of the generic formulae ([Cy.sub.3]PO)Sb[X.sub.3] (X = F (1a), Cl (1b), or Br (1c)), [([Cy.sub.3]PO).sub.2]Sb[X.sub.3] (X = F (2a), Cl (2b), or Br (2c)), and ([Cy.sub.3]PS)Sb[X.sub.3] (X = Cl (3b), Br (3c), or I (3d)) were synthesized via the treatment of solutions of Sb[X.sub.3] with OP[Cy.sub.3] and SP[Cy.sub.3], respectively. Derivatives of ([Cy.sub.3]PO)Sb[X.sub.3] were characterized by single crystal X-ray diffraction for 1a and 1b and crystallize as dimers through symmetry related intermolecular Sb- X interactions, providing the first structurally characterized examples of this class of complex. Derivatives of ([Cy.sub.3]PS)Sb[X.sub.3] (3b-3c) adopt analogous dimeric structures in the solid state. The solid-state structure of [([Cy.sub.3]PO).sub.2]Sb[Cl.sub.3] (2b) is consistent with the previously reported structures of bis-phosphine oxide complexes of antimony(III), with a square pyramidal Sb center and cis-configured OP[Cy.sub.3] ligands. The phosphine chalcogenide complexes of Sb[X.sub.3] display configurations that are consistent with the perceived trans-labilizing properties of the ligands/substituents. Key words: antimony, coordination chemistry, chalcogens, Lewis acid. Nous avons synthetise trois series de complexes formes a partir de chalcogenures de phosphine et d'halogenures d'antimoine(III), Sb[X.sub.3] (X = F, Cl, Br ou I), et les avons caracterises a l'aide de methodes spectroscopiques et cristallographiques. Les complexes de formules generiques ([Cy.sub.3]PO)Sb[X.sub.3] (X = F (1a), Cl (1b), ou Br (1c)), [([Cy.sub.3]PO).sub.2]Sb[X.sub.3] (X = F (2a), Cl (2b), ou Br (2c)) et ([Cy.sub.3]PS)Sb[X.sub.3] (X = Cl (3b), Br (3c), ou I (3d)) ont ete prepares par traitement de solutions de Sb[X.sub.3] avec OP[Cy.sub.3] et SP[Cy.sub.3], respectivement. Les derives de type ([Cy.sub.3]PO)Sb[X.sub.3] ont ete caracterises par diffraction des rayons X d'un cristal unique des complexes 1a et 1b, lesquels se cristallisent sous forme de dimeres en raison d'interactions intermoleculaires Sb-X attribuables a la symetrie, ce qui en fait les premiers exemples structurellement caracterises de cette classe de complexes. Les derives de type ([Cy.sub.3]PS)Sb[X.sub.3], les complexes 3b-3c, adoptent a l'etat solide des structures dimeriques analogues. La structure a l'etat solide du complexe [([Cy.sub.3]PO).sub.2]Sb[Cl.sub.3] (2b) correspond aux structures de complexes formes d'oxyde de bis-phosphine et d'antimoine(III) qui ont ete decrites precedemment dans la litterature et se caracterise par un atome central d'antimoine a geometrie pyramidale a base carree et des ligands OP[Cy.sub.3] de configuration cis. Les complexes formes de chalcogenures de phosphine et de Sb[X.sub.3] presentent des configurations qui sont compatibles avec l'effet<>que l'on attribue aux ligands ou aux substituants. [Traduit par la Redaction] Mots-cles: antimoine, chimie de coordination, chalcogenes, acide de Lewis., Introduction Antimony(III) halides, Sb[X.sub.3], offer a diverse structural and reaction (1,2) chemistry due in part to their potential to behave as both Lewis bases, by virtue of a lone pair [...]

Titanium dioxide (Ti[O.sub.2]) nanowires with two different dimensions (i.e., < 100 nm and ~200 nm in diameter) were synthesized and studied under high pressure up to 37 GPa by Raman spectroscopy and synchrotron X-ray diffraction. Direct anatase to baddeleyite phase transitions were observed in both samples upon compression, but with different onset pressures. The observed phase transitions are in contrast to bulk Ti[O.sub.2], where the anatase phase transforms to α-Pb[O.sub.2] phase and then the baddeleyite phase. Compressibility of the anatase and baddeleyite phases was found different than both nanocrystals and the corresponding bulk materials. Our comparative study demonstrated not only that the morphology of Ti[O.sub.2] nanowire substantially influences the high pressure behaviors, but dimensions play a determining role in terms of transformation pressures, phase stability regions, and compressibility. Key words: high pressure, Ti[O.sub.2] nanowires, phase transformation, Raman spectroscopy, synchrotron radiation. Resume: Des nanofils de dioxyde de titane (Ti[O.sub.2]) de deux dimensions differentes (c.-a-d. de diametres < 100 nm et ~200 nm) ontete synthetises et analyses sous de hautes pressions allant jusqu'a 37 GPa par spectroscopie Raman et diffraction des rayons X synchrotron. Des transitions de phase directes anatase-baddeleyite ont ete observees dans les deux echantillons sous l'effet d'une compression, mais avec une pression exercee differente pour chaque echantillon. Les transitions de phase observees contrastent avec celles du Ti[O.sub.2] brut avec lequel la phase anatase se transforme en une phase α-Pb[O.sub.2] puis en une phase baddeleyite. La compressibilite des phases anatase et baddeleyite s'est averee differente de celle des deux nanocristaux et des materiaux bruts correspondants. Notre etude comparative a montre que non seulement la morphologie du nanofil de Ti[O.sub.2] influe grandement sur les comportements a haute pression mais egalement que leurs dimensions joue un role determinant en ce qui concerne les pressions de transformation, les domaines de stabilite des phases et la compressibilite. [Traduit par la Redaction] Mots-cles: haute pression, nanofils de Ti[O.sub.2], transformation de phase, spectroscopie Raman, rayonnement synchrotron., Introduction Titanium dioxide (Ti[O.sub.2]), or titania, is a well-known semiconductor with a wide band gap. Ti[O.sub.2] exhibits a rich phase diagram including more than seven polymorphs. The most abundant forms, [...]

Zwitterionic dicoordinate phosphorus(I) compounds (1 and 2), formally a charge neutral triphosphenium ion or phosphanide, are shown to coordinate to a variety of late transition metals. The reaction of the phosphanide proligands with [{Rh(COD)Cl}.sub.2] results in an equilibrium process that varies as a function of temperature or reaction stoichiometry. Palladium(II) compounds have a tendency to chlorinate the borate backbone while giving dimeric coordination compounds (1Pd) and also a decomposition product (3) where the P(I) atom was replaced. Both 'lone pairs' of electrons on phosphorus are utilized simultaneously in the dominant product from the reaction of 1 and [[Pt[Me.sub.2](pμS[Me.sub.2])].sub.2], while each platinum center ortho-metallated a phenyl substituent on the flanking phosphorus atoms (1Pt). Stable, isolable, and fully characterized dimeric mercury complexes (1Hg and 2Hg) are produced nearly quantitatively from the reaction of the phosphanide proligand with Hg[Cl.sub.2]. All compounds described were structurally characterized using single crystal X-ray diffraction and represent a growing series of zwitterionic P(I) coordination compounds that cannot be isolated when a cationic triphosphenium ion is used. Key words: phosphorus, zwitterions, coordination chemistry, main group chemistry. Resume: Les composes zwitterioniques bis-coordonnes de phosphore(I) (1 et 2), qui sont en fait des ions triphosphenium neutres ou des phosphanures, se sont reveles capables de se coordonner a divers metaux de transition de fin de serie. La reaction des proligands phosphanures avec le complexe [[Rh(COD)Cl].sub.2] entraine un processus d'equilibre qui varie en fonction de la temperature ou de la strechiometrie de la reaction. Les composes de palladium(II) ont tendance a chlorer la chaine principale boratee et a donner, pour leur part, les composes de coordination dimeriques (1Pd) ainsi que le produit de decomposition (3) dans lequel l'atome de P(I) a ete remplace. Les deux doublets non liants des electrons du phosphore sont engages simultanement dans le produit majoritaire provenant de la reaction entre le compose 1 et le complexe [[Pt[Me.sub.2](μ-S[Me.sub.2])].sub.2]. Quant aux noyaux de platine, chacun d'eux s'est insere en position ortho de l'un des substituants phenyles de l'atome de phosphore voisin (1Pt). Des complexes dimeriques de mercure (1Hg et 2Hg) stables, isolables et entierement caracterises sont produits de facon quasi quantitative par la reaction du proligand phosphanure avec le Hg[Cl.sub.2]. Tous les composes decrits ont ete structurellement caracterises par diffraction des rayons X d'un cristal unique et representent une serie en expansion de composes zwitterioniques de coordination P(I) ne pouvant pas etre isoles lorsqu'un cation triphosphenium est utilise. [Traduit par la Redaction] Mots-cles: phosphore, zwitterions, chimie de coordination, chimie des elements du groupe principal., Introduction Tertiary phosphines and N-heterocyclic carbenes are ubiquitous two-electron donor ligands that have been shown to form stable coordination compounds to essentially every transition metal or main group element spanning [...]

Recent advances in Au-thiolate nanocluster synthesis have allowed the total structural determination of several nanoclusters by X-ray crystallography. The high-precision structural information of these nanoclusters enables atomic site-specific analysis of local structure and electronic character. In this work, a site-specific comparative study of [Au.sub.102][(SR).sub.44] and [Au.sub.25][(SR).sub.18] was conducted to elucidate the size and site effects on the local environment and electronic character of their common surface structural unit, the -SR-Au-SR-Au-SR- 'double-staple' motif. Simulation of the pseudo-radial distribution function from extended X-ray absorption fine structure (EXAFS) shows a significant difference in their local environments despite their identical geometric shape. Local density of states (l-DOS) calculations consistently reveal the difference in their electronic characters for gold d-electron density and d-DOS position. These differences are then related to the unique aurophilic interactions and size--or site-dependent electronic character of Au atoms in the double-staple motif. The differing local structure and electronic behaviour of the 'double-staple' motif in [Au.sub.102][(SR).sub.44] and [Au.sub.25][(SR).sub.18] highlight the significance of both size and site effects on the surface structure and electronic property of Au-thiolate nanoclusters. The theoretical results may also be useful in the interpretation of future experimental XAFS and X-ray photoelectron spectroscopy (XPS) data of these nanoclusters. Key words: gold nanoclusters, thiolate, [Au.sub.25], [Au.sub.102], X-ray absorption fine structure, local density of states. De recents progres dans la synthese de nanoagregats d'or-thiolate ont permis de determiner l'ensemble de la structure de plusieurs nanoagregats par radiocristallographie. L'information structurelle en haute definition de ces nanoagregats permet une analyse localisee a l'echelle atomique de la structure et des proprietes electroniques locales d'un point particulier. Dans le cadre de ces travaux, une etude comparative d'un point particulier sur les nanoagregats [Au.sub.102][(SR).sub.44] et [Au.sub.25][(SR).sub.18] a ete menee pour determiner les effets de la taille et de la position sur l'environnement structurel et electronique local de leur unite structurelle commune de surface, le motif en << double agrafe >> -SR-Au-SR-Au-SR-. La simulation de la fonction de distribution pseudo-radiale obtenue par spectroscopie EXAFS (extended X-ray absorption fine structure) montre d'importantes differences entre leurs environnements locaux malgre leur forme geometrique identique. Les calculs de la densite d'etats locale (l-DOS) ont revele une difference systematique entre leurs proprietes electroniques sur les plans de la densite des electrons d de l'or et de la position de la densite d'etats des electrons d. Ces differences ont ensuite ete reliees aux interactions aurophiles uniques et aux proprietes electroniques qui dependent de la taille et de la position des atomes d'or dans le motif en double agrafe. Les divergences locales de structure et de comportement electronique du motif en double agrafe entre les nanoagregats [Au.sub.102][(SR).sub.44] et [Au.sub.25][(SR).sub.18] font ressortir l'importance tant des effets lies a la taille et a la position sur la structure de la surface que des proprietes electroniques des nanoagregats d'or-thiolate. Les resultats theoriques pourraient servir a interpreter des donnees futures de spectroscopie EXAFS et de spectroscopie de photoelectrons X. [Traduit par la Redaction] Mots-cles: nanoagregats d'or, thiolate, [Au.sub.25], [Au.sub.102], spectroscopie EXAFS, densite d'etats locale., Introduction Small Au-thiolate nanoclusters with precisely controlled composition are of interest because of their unique atomic structure and quantum-size-effect dominated properties. (1, 2) The electronic properties of these nanoclusters are [...]