Structure and Bonding of Isoleptic Coinage Metal (Cu, Ag, Au) Dimethylaminonitrenes in the Gas Phase

Dimethylaminonitrene complexes of IMesM+ (IMes = 1,3-bis(2,4,6-trimethylphenyl)- imidazol-2-ylidene; M = Cu, Ag, Au) were prepared in the gas phase and structurally characterized by high-resolution infrared spectroscopy of the cold species, ion-molecule reactions, and DFT computations. We measured the binding energies of the nitrene fragment to the IMesM moiety by energy-resolved collision-induced dissociation experiments in the gas phase, affording a trend in bond strength of M = Cu ? Au > Ag. This trend is explained in terms of a detailed metal-nitrogen bonding analysis, from which relativistic effects on the bonding were assessed. Various density functionals were evaluated for reproducing the observed thermochemical data and Truhlar's M06 functional was found to give the best agreement.

Binding of Organometallic Ruthenium(II) and Osmium(II) Complexes to an Oligonucleotide: A Combined Mass Spectrometric and Theoretical Study

Antoine Dorcier, Paul Joseph Dyson, Christian Gossens, Ursula Röthlisberger, Rosario Scopelliti, Ivano Tavernelli

Ru(II) and Os(II) p-cymene dichloride complexes with either a pta (1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane) or [pta-Me]Cl ligand which exhibit anticancer activity were prepd. and characterized by 1H and 31P NMR spectroscopy and mass spectrometry. Three of the complexes, viz. [Os(h6-p-cymene)Cl2(pta)] and [M(h6-p-cymene)Cl2(pta-Me)]Cl (M = Ru, Os), also were characterized by single-crystal x-ray diffraction. The pta complexes are selective anticancer agents, whereas the pta-Me+ complexes are indiscriminate and damage both cancer and healthy cells but represent models for the protonated pta adduct which was implicated in drug activity. To establish a link between their biol. activity and the effect they have on DNA (a likely in vivo target), the reactivity of the complexes toward a 14-mer oligonucleotide (5'-ATACATGGTACATA-3') was studied using electrospray ionization mass spectrometry. The complexes bind to the oligonucleotide with loss of chloride and in some cases loss of the arene. Loss of arene appears to be most facile with the Ru-pta complexes but also takes place with the Ru-pta-Me complexes, whereas arene loss is not obsd. for the Os complexes. As pH is reduced, increased binding to the oligonucleotide is obsd., as evidenced from mass spectrometric relative intensities. Binding energies between the metal centers and the surrounding ligands were calcd. using d. functional theory (DFT). The calcd. energies rationalize the exptl. obsd. tendencies for arene loss and show that the pta ligands are relatively strongly bound. Exchange of metal center (Ru vs. Os), methylation or protonation of the pta ligand, or change of the arene (p-cymene vs. benzene) results in significant differences in the metal-arene binding energies while leaving the metal-phosphine bond strength essentially unchanged. Significantly lower binding energies and reduced hapticity are predicted for the exchange of arene by nucleobases. The latter show higher binding energies for N s-bonding than for p-bonding. [on SciFinder (R)]

2005

Role of Adsorbed H, C, O, and CO on the Atomic Structure of Free and MgO(100)-Supported Ir-4 Clusters: An ab Initio Study

Alfonso Baldereschi, Zeljko Sljivancanin, Vladan Stevanovic

We applied density functional theory based on ultrasoft pseudopotentials to study the structural properties of Ir-4 clusters both in the gas phase and adsorbed on a MgO(100) surface. To resolve the discrepancy between experimental data which suggest a tetrahedral structure for Ir-4 and theoretical results which show a strong preference for the square isomer, we investigated the effect of several adsorbates on the equilibrium atomic structure of the clusters. Calculated binding energies of a single H, C, or O atom, as well as one CO or OH molecule, to three stable Ir-4 isomers indicate that C or CO adsorption significantly influences the relative stability of Ir-4 isomers. For MgO(100)-supported Ir-4, atomic carbon is able to change the isomer preference from the square to the tetrahedral geometry.

2010

Low-strain interface models for epitaxial graphene on SiC(0001)

Alfredo Pasquarello, Gabriele Sclauzero

A set of low-strain commensurate interface structures for epitaxial graphene on SiC(0001) are obtained by combining rotated graphene supercells with m x m or m root 3 x m root 3R30 degrees SiC cells. For two among the interfaces with lowest strain, corresponding to 4 x 4 and 6 root 3 x 6 root 3R30 degrees SiC periodicities, we analyze the binding energy of the graphene/SiC(0001) interface in terms of bond energies resulting from the (partial) saturation of individual Si dangling bonds by C atoms of graphene. These bond energies are determined as a function of the relative lateral displacement between the surface Si atoms and the graphene honeycomb. We find that this model energy does not explain the variation of the binding energies obtained from direct density functional calculations for the full interfacial systems. Moreover, for a given interface, the lateral rearrangements of the Si and C atomic positions found upon relaxation do not lead to any significant increase of the model binding energy. These results indicate that the deformations of the graphene layer cannot be neglected in the modeling of the binding energy of the graphene/SiC(0001) system. (C) 2011 Elsevier B.V. All rights reserved.

Elsevier2012

Binding of Organometallic Ruthenium(II) and Osmium(II) Complexes to an Oligonucleotide: A Combined Mass Spectrometric and Theoretical Study

Antoine Dorcier, Paul Joseph Dyson, Christian Gossens, Ursula Röthlisberger, Rosario Scopelliti, Ivano Tavernelli

2005