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1.
Dario Braga Fabrizia Grepioni Paul J. Dyson Brian F. G. Johnson 《Journal of Cluster Science》1992,3(3):297-311
The molecular and crystal structures of a number of ruthenium and osmium clusters of nuclearity between three and six containing arene fragments such as C6H6, C6H3Me3, C6H4Me2 and C6H5Me have been investigated. Attention has been focused on the relationship between the terminal (
6-coordination) and face-capping (
3:
2:
2:
2-coordination) bonding modes. Empirical packing potential energy calculations have been employed to investigate the intermolecular organization in the crystal. It has been shown that the arene fragments in mono-arene clusters form ribbons, while in bis-arene clusters graphitic-like interactions throughout the crystal are established. The factors controlling the ease of arene reorientational motion in the solid state has also been investigated in relation to the shape, size and geometry of the molecules and of their interlocking modes. 相似文献
2.
Maria Helena Araujo Maria D. Vargas Anthony G. Avent Fabrizia Grepioni 《Journal of organometallic chemistry》2004,689(22):3513-3519
The reactions of [HIr4(CO)9(Ph2PCCPh)(μ-PPh2)] (1) or [Ir4(CO)8(μ3-η2-HCCPh)(μ-PPh2)2] (2) with HCCPh gave two isomeric forms of [Ir4(CO)6(μ3-η2-HCCPh)(μ2-η4-C4H2Ph2)(μ-PPh2)2] (3 and 4) in good yields as the only products. These compounds were characterized with analytical and spectroscopic data including 1H, 13C and 31P NMR (1 and 2D) spectroscopy and their molecular structures were established by X-ray diffraction studies. Compounds 3 and 4 exhibit the same distorted butterfly metal polyhedral arrangement of metal atoms with two μ-PPh2 that occupy different positions in the structures of the two isomers. Both molecules contain a HCCPh ligand bonded in a μ3-η2-// mode to one of the wings of the butterfly and a metallacyclic ring, which resulted from head-to-tail coupling, in the case of [Ir4(CO)6(μ3-η2-HCCPh){μ2-η4-(H)CC(Ph)C(H)C(Ph)}(μ-PPh2)2] (3) and tail-to-tail coupling, in that of [Ir4(CO)6(μ3-η2-HCCPh){μ2-η4-(H)CC(Ph)C(Ph)C(H)}(μ-PPh2)2] (4), and which is linked to two metal atoms of the second wing of the butterfly. 相似文献
3.
Braga D Maini L Polito M Mirolo L Grepioni F 《Chemical communications (Cambridge, England)》2002,(24):2960-2961
Solvent-free reactions with molecular systems have been exploited to prepare hybrid organic-organometallic solids: grinding of the complex [Fe(eta 5-C5H4COOH)2] with solid bases B generates quantitatively the corresponding hydrogen bonded salts [Fe(eta 5-C5H4COOH)(eta 5-C5H4COO)][HB] (B = 1,4-diazabicyclo[2.2.2]octane, 1,4-phenylenediamine); gas-solid reactions are also possible with volatile bases. 相似文献
4.
Fabrizi de Biani F Ienco A Laschi F Leoni P Marchetti F Marchetti L Mealli C Zanello P 《Journal of the American Chemical Society》2005,127(9):3076-3089
The reaction between equimolar amounts of Pt(3)(mu-PBu(t)()(2))(3)(H)(CO)(2), Pt(3)()H, and CF(3)SO(3)H under CO atmosphere affords the triangular species [Pt(3)(mu-PBu(t)()(2))(3)(CO)(3)]X, [Pt(3)()(CO)(3)()(+)()]X (X = CF(3)SO(3)(-)), characterized by X-ray crystallography, or in an excess of acid, [Pt(6)(mu-PBu(t)()(2))(4)(CO)(6)]X(2), [Pt(6)()(2+)()]X(2)(). Structural determination shows the latter to be a rare hexanuclear cluster with a Pt(4) tetrahedral core formed by joining the unbridged sides of two orthogonal Pt(3) triangles. The dication Pt(6)()(2+)() features also extensive redox properties as it undergoes two reversible one-electron reductions to the congeners [Pt(6)(mu-PBu(t)()(2))(4)(CO)(6)](+) (Pt(6)()(+)(), E(1/2) = -0.27 V) and Pt(6)(mu-PBu(t)()(2))(4)(CO)(6) (Pt(6)(), E(1/2) = -0.54 V) and a further quasi-reversible two-electron reduction to the unstable dianion Pt(6)()(2)()(-)() (E(1/2) = -1.72 V). The stable radical (Pt(6)()(+)()) and diamagnetic (Pt(6)()) species are also formed via chemical methods by using 1 or 2 equiv of Cp(2)Co, respectively; further reduction of Pt(6)()(2+)() causes fast decomposition. The chloride derivatives [Pt(6)(mu-PBu(t)()(2))(4)(CO)(5)Cl]X, (Pt(6)()Cl(+)())X, and Pt(6)(mu-PBu(t)()(2))(4)(CO)(4)Cl(2), Pt(6)()Cl(2)(), observed as side-products in some electrochemical experiments, were prepared independently. The reaction leading to Pt(3)()(CO)(3)()(+)() has been analyzed with DFT methods, and identification of key intermediates allows outlining the reaction mechanism. Moreover, calculations for the whole series Pt(6)()(2+)() --> Pt(6)()(2)()(-)()( )()afford the otherwise unknown structures of the reduced derivatives. While the primary geometry is maintained by increasing electron population, the system undergoes progressive and concerted out-of-plane rotation of the four phosphido bridges (from D(2)(d)() to D(2) symmetry). The bonding at the central Pt(4) tetrahedron of the hexanuclear clusters (an example of 4c-2e(-) inorganic tetrahedral aromaticity in Pt(6)()(2+)()) is explained in simple MO terms. 相似文献
5.
Francesco Demartin Fabrizia Fabrizi de Biani Cristina Femoni Maria Carmela Iapalucci Giuliano Longoni Piero Macchi Piero Zanello 《Journal of Cluster Science》2001,12(1):61-74
The [Ni36Pt4(CO)45]6- and [Ni37Pt4(CO)46]6- clusters have been obtained in mixture upon reaction in acetonitrile of [Ni6(CO)12]2- salts with K2PtCl4 in a 2.5:1 molar ratio. The two hexaanions were indistinguishable by spectroscopic techniques. Crystallization of their trimethylbenzylammonium salts led to crystals of composition 0.5[NMe3CH2Ph]6[Ni36Pt4(CO)45]-0.5[NMe3CH2Ph]6[Ni37Pt4(CO)46]·C3H8O, hexagonal,space group P63 (No. 173), a=17.853(9), c=27.127(13) Å, Z=2; final R=0.057. The metal core of the [Ni36Pt4(CO)45]6- anion consists of a Pt4 tetrahedron fully encapsulated in a shell of 36 Ni atoms belonging to a very distorted and incomplete 5 tetrahedron. The [Ni37Pt4(CO)46]6- hexaanion derives from the former by capping the unique triangular face of the metal polyhedron with an additional Ni(CO) fragment. The [Ni36Pt4(CO)45]6--[Ni37Pt4(CO)46]6- mixture is rapidly degraded to the known [Ni9Pt3(CO)21]4- cluster by exposure to carbon monoxide. Its reaction with protic acids initially affords the corresponding [H6-nNi36Pt4(CO)45]n--[H6-nNi37Pt4(CO)46]n- (n=5, 4) derivatives, and eventually leads to rearrangement to the known [H6-n Ni38Pt6(CO)48]n- species. Both [Ni36Pt4(CO)45]6--[Ni37Pt4(CO)46]6- and [HNi36Pt4(CO)45]5--[HNi37Pt4(CO)46]5- mixtures have been chemically and electrochemically reduced to their corresponding [Ni36Pt4(CO)45]n--[Ni37Pt4(CO)46]n- (n=7–9) and [HNi36Pt4(CO)45]n--[HNi37Pt4(CO)46]n- (n=6–8) mixtures. 相似文献
6.
Ab initio CASPT2//CASSCF relaxation path computations are employed to determine the intrinsic (e.g., in vacuo) mechanism underlying the rise and decay of the luminescence of the anionic form of the green fluorescent protein (GFP) fluorophore. Production and decay of the fluorescent state occur via a two-mode reaction coordinate. Relaxation along the first (totally symmetric) mode leads to production of the fluorescent state that corresponds to a planar species. The second (out-of-plane) mode controls the fluorescent state decay and mainly corresponds to a barrierless twisting of the fluorophore phenyl moiety. While a "space-saving" hula-twist conical intersection decay channel is found to lie only 5 kcal mol(-1) above the fluorescent state, the direct involvement of a hula-twist deformation in the decay is not supported by our data. The above results indicate that the ultrafast fluorescence decay observed for the GFP chromophore in solution is likely to have an intrinsic origin. The possible effects of the GFP protein cavity on the fluorescence lifetime of the investigated chromophore model are discussed. 相似文献
7.
Migani A Gentili PL Negri F Olivucci M Romani A Favaro G Becker RS 《The journal of physical chemistry. A》2005,109(39):8684-8692
The efficiency of the photochemical ring-opening of chromenes (or benzopyrans) depends on the vibronic transition selected by the chosen excitation wavelength. In the present work, ab initio CASPT2//CASSCF calculations are used to determine the excited-state ring-opening reaction coordinate for 2H-chromene (C) and 2,2-diethyl-2H-chromene (DEC) and provide an explanation for such an unusual mode-dependent behavior. It is shown that excited-state relaxation and decay occur via a multimodal and barrierless (or nearly barrierless) reaction coordinate. In particular, the relaxation out of the Franck-Condon involves a combination of in-plane skeletal stretching and out-of-plane modes, while the second part of the reaction coordinate is dominated exclusively by a different out-of-plane mode. Population of this last mode is shown to be preparatory with respect to both C-O bond breaking and decay via an S(1)/S(0) conical intersection. The observed mode-dependent ring-opening efficiency is explained by showing that the vibrational mode corresponding to the most efficient vibronic transition has the largest projection onto the out-of-plane mode of the reaction coordinate. To support the computationally derived mechanism, we provide experimental evidence that the photochemical ring-opening reaction of 2,2-dimethyl-7,8-benzo(2H)chromene, that similarly to DEC exhibits a mode-dependent photoreaction, has a low ( approximately 1 kcal mol(-1)) activation energy barrier. 相似文献
8.
Molecular Size and Electronic Structure Combined Effects on the Electrogenerated Chemiluminescence of Sulfurated Pyrene‐Cored Dendrimers 下载免费PDF全文
Dr. Giovanni Valenti Dr. Andrea Fiorani Dr. Simone Di Motta Dr. Giacomo Bergamini Prof. Marc Gingras Prof. Paola Ceroni Prof. Fabrizia Negri Prof. Francesco Paolucci Prof. Massimo Marcaccio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):2936-2947
The electrochemistry, photophysics, and electrochemically generated chemiluminescence (ECL) of a family of polysulfurated dendrimers with a pyrene core have been thoroughly investigated and complemented by theoretical calculations. The redox and luminescence properties of dendrimers are dependent on the generation number. From low to higher generation it is both easier to reduce and oxidize them and the emission efficiency increases along the family, with respect to the polysulfurated pyrene core. The analysis of such data evidences that the formation of the singlet excited state by cation–anion annihilation is an energy‐deficient process and, thus, the ECL has been justified through the triplet–triplet annihilation pathway. The study of the dynamics of the ECL emission was achieved both experimentally and theoretically by molecular mechanics and quantum chemical calculations. It has allowed rationalization of a possible mechanism and the experimental dependence of the transient ECL on the dendrimer generation. The theoretically calculated Marcus electron‐transfer rate constant compares very well with that obtained by the finite element simulation of the whole ECL mechanism. This highlights the role played by the thioether dendrons in modulating the redox and photophysical properties, responsible for the occurrence and dynamics of the electron transfer involved in the ECL. Thus, the combination of experimental and computational results allows understanding of the dendrimer size dependence of the ECL transient signal as a result of factors affecting the annihilation electron transfer. 相似文献
9.
A Highly Luminescent Tetramer from a Weakly Emitting Monomer: Acid‐ and Redox‐Controlled Multiple Complexation by Cucurbit[7]uril 下载免费PDF全文
Dr. Giacomo Bergamini Andrea Fermi Marianna Marchini Mirko Locritani Prof. Alberto Credi Prof. Margherita Venturi Prof. Fabrizia Negri Prof. Paola Ceroni Dr. Massimo Baroncini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):7054-7060
The tetrahedral, shape‐persistent molecule 1 4+, containing four pyridylpyridinium units connected through a central carbon atom, exhibits unexpected photophysical properties including a substantially redshifted absorption (2350 cm?1) and a very strong fluorescence (Φem=40 %), compared with the monomer 2 + (Φem=0.4 %). Density functional theory calculations on the structure and spectroscopic properties of 1 4+ and 2 + show that exciton interactions, homoconjugation, and orbital nature account for the observed differences in their photophysical properties. The protonated tetramer binds four cucurbit[7]uril molecules and the host/guest interactions can be controlled by chemical (acid/base) as well as redox stimuli. 相似文献
10.
Yue W Gao J Li Y Jiang W Di Motta S Negri F Wang Z 《Journal of the American Chemical Society》2011,133(45):18054-18057
Tetracene tetracarboxylic diimides have been synthesized based on direct double ring extension of electron-deficient naphthalene diimides involving metallacyclopentadienes. Atomic structure and electronic transitions responsible for their NIR absorption spectra are investigated with quantum-chemical calculations. In light of their unique structure and admirable photophysical and electronic properties, this new molecular skeleton is promising candidate for n-type semiconductors. 相似文献