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Full geometry optimization using the BP86 and B3LYP methods has been carried out for all of the low-energy isomers of half-sandwich [L.sub.3]M(Tphn) (Tphn = triphenylene, M = Ti-Ni, and [L.sub.3] = [(CO).sub.3], [Cp.sup.-]) and sandwich M[(Tphn).sub.2] (Tphn = triphenylene and M = Ti, Cr, Fe, Ni) structures. Depending on the electron richness of the molecule and the nature of the metal, a complete rationalization of the bonding in triphenylene complexes has been provided. The triphenylene adopts various hapticities from [η.sup.2] to [η.sup.6], some of them involving full or partial coordination of the [C.sub.6] ring and shown to be quite flexible with respect to the ground spin state. The triphenylene behavior remains dependent on the electron-withdrawing and electron-donor properties of the [(CO).sub.3]M and CpM fragments, respectively. For the sandwich complexes, both triphenylene ligands prefer to behave differently depending on the coordination mode to satisfy the metal electron demand. Key words: DFT method, orbital interactions, spin states, coordination chemistry, various hapticities, NBO analysis. A l'aide des methodes BP86 et B3LYP, nous avons effectue l'optimisation complete de la geometrie pour tous les isomeres de basse energie des structures en demi-sandwich [L.sub.3]M(Tphn) (Tphn = triphenylene, M = Ti-Ni et [L.sub.3] = [(CO).sub.3], [Cp.sup.-]) et en sandwich M[(Tphn).sub.2] (Tphn = triphenylene et M = Ti, Cr, Fe, Ni). Nous avons aussi effectue une rationalisation complete des liaisons dans les complexes de triphenylene en fonction de la richesse electronique de la molecule et de la nature du metal. Nous avons observe que triphenylene adopte diverses hapticites allant de [η.sup.2] a [η.sup.6], dont certaines font intervenir une coordination totale ou partielle du noyau C6 qui s'est revele passablement flexible par rapport a l'etat fondamental de spin. Le comportement du triphenylene demeure fonction des effets electroattracteurs et electrodonneurs propres aux fragments [(CO).sub.3]M et CpM, respectivement. Quant aux complexes en sandwich, afin de satisfaire la demande electronique du metal, les deux ligands triphenylene montrent une preference de comportement qui differe selon le mode de coordination. [Traduit par la Redaction] Mots-cles: methode DFT, interactions orbitaires, etats de spin, chimie de coordination, hapticites diverses, analyse des NBO., Introduction Polycyclic arenes known as polycyclic aromatic hydrocarbons (PAHs) constitute a large class of organic compounds (1) and have attracted a great deal of interest in material science due to [...]

The properties of metal-metal bonding for transition metal homonuclear diatomics from groups 10, 11 and 12 are studied within the framework of the quantum theory of atoms in molecules (QTAIM) at the coupled cluster CCSD and CCSD(T) levels of theory. A novel approximate method developed by Keith and Frisch is used to augment electron densities calculated with pseudopotentials with the missing relativistic core densities to obtain approximations to the total densities of the dimers. The calculated delocalization indices for group 10 dimers are: [Ni.sub.2] (1.6), [Pd.sub.2] (0.44, an outlier in the group), and [Pt.sub.2] (1.8); for group 11 dimers: [Cu.sub.2] and [Ag.sub.2] (1.01), and [Au.sub.2] (1.13), all covalent bonds; for group 12: [Zn.sub.2] (0.06), [Cd.sub.2] (0.08), and [Hg.sub.2] (0.09), all consistent with weak van der Waals complexes. The picture of bonding obtained by examining the values of the electron density at the bond critical points is consistent with the one obtained on the basis of these delocalization indices. A curious linear (instead of exponential) dependence of the delocalization index on the electron density at the bond critical point is presented here as an observation and will be investigated in more depth in later work. Several correlations between bond properties and bond dissociation energies are also explored. It is found that, with the exception of the [Ni.sub.2] dimer that exhibits considerable multi-reference character, there are correlations between the calculated bond dissociation energies of the studied diatomics and several bond critical point properties. These correlations are novel as they span a set of bonds between different pairs of elements, while traditionally these correlations were reported for bonds between the same pair or elements but with different substituents. Key words: topology of the electron density, chemical bonding in transition metals, quantum theory of atoms in molecules, QTAIM, metal-metal bonding. Resume : Les proprietes des liaisons metal-metal pour les dimeres homonucleaires des metaux de transition des groupes 10,11 et 12 sont etudies dans le cadre de la theorie quantique des atomes-dans-les-molecules (QTAIM) en faisant appel aux niveaux de theorie CCSD et CCSD (T). Une nouvelle methode developpee par Keith et Frisch est utilisee pour augmenter des densites electroniques calculees a l'entremise de pseudo potentiels avec les densites de cceur relativistes manquantes pour obtenir des approximations aux densites totales des dimeres. Les indices de delocalisation calcules pour les dimeres du groupe 10 : [Ni.sub.2] (1.6), [Pd.sub.2] (0.44, qui est en ecart du reste du groupe) et [Pt.sub.2] (1.8); pour les dimeres du groupe 11: [Cu.sub.2] et [Ag.sub.2] (1.01) et [Au.sub.2] (1.13), toutes les liaisons etant covalentes; et pour le groupe 12 : [Zn.sub.2] (0.06), [Cd.sub.2] (0.08) et [Hg.sub.2] (0.09) indiquant de faibles liaisons du type van der Waals. L'image qui emerge a propos de la nature de la liaison chimique obtenu en examinant les valeurs de la densite electronique aux points critiques est completement en accord avec celle obtenue sur la base des indices de delocalisation. Une curieuse dependance lineaire (au lieu d'exponentielle) de l'indice de delocalisation sur la densite electronique au point critique est presente ici comme une observation et sera enquete en plus de profondeur dans un travail future. Plusieurs correlations entre les proprietes des liaisons chimiques et les energies de leur dissociation sont aussi explorees. Il est constate que, a l'exception du dimer de [Ni.sub.2], dote d'un caractere multireferenciel considerable, il existe des correlations entre les energies de dissociation des dimeres etudies et plusieurs des proprietes de leur point critiques de liaisons. Ces correlations sont nouvelles car ils s'etendent sur un ensemble de liaisons entre de paires d'elements differentes, quand traditionnellement ces correlations ont ete trouvees pour les liaisons entre une meme paire d'element, mais avec des substituents differents. Mots-cles: la topologie de la densite electronique, la liaison chimique des metaux de transition, la theorie quantique des atomes dans les molecules (QTAIM/TQADM), la liaison metal-metal., Introduction Transition metal dimers have been studied for a number of years (1) and continue to provide challenges for ab initio methods. As noted by Yanagisawa, Tsuneda, and Hirao, nonhybrid [...]