Electrons coordinates

A change in hapticity of the Cp ligand in 1 from q3/5 to ri1 should lead to a drastic change in the character of the molecule whereas the 7t-bonded species (I) can be regarded as a hyper-coordinated, electronically over-saturated and thus nucleophilic silylene, the a-bonded species (II) represents an example of an electron deficient and thus electrophilic silylene. 

H and 13C NMR. These are rare examples of thermally stable monomeric germaimines. At room temperature die mesityl and die N-Me groups are not equivalent. At 55 °C the split signals coalesce. This is possibly due to interaction between Ge and NMe2. Stability is adduced to intramolecular Ge—O coordination, electron withdrawal by the C=0 group and bulkiness of die mesityl groups. ... 

Whereas changes in hapticity are normally required for changes in the number of coordinated electron pairs, acetylene and other triple-bonded ligands exhibit the... 

Background Philosophy. Within the framework of the Born-Oppenheimer approximation (JJ ), the solutions of the Schroedin-ger equation, Hf = Ef, introduce the concept of molecular structure and, thereby, the total energy hyperspace provided that the electronic wave function varies only slowly with the nuclear coordinates, electronic energies can be calculated for sets of fixed nuclear positions. The total energies i.e. the sums of electronic energy and the energy due to the electrostatic re-... 

In addition to their spatial coordinates, electrons are characterized by a spin, described by a coordinate s, which can have two discrete values, usually called up and down. Wave functions for a system containing more than one electron are analogous functions of the coordinates of all the electrons ... 

Table XIII (189-199) gives details of solid-state lithium amide monomeric complexes (69)—(87). These include just three [(79), (80), and (87)] solvent-separated ion pairs. The remainder are contact-ion pairs, each with an (amido)N—Li bond. Association to dimers or higher oligomers is prevented sterically. The size of the R and/or R group in the RR N- anions can lead to monomers even when Li+ is complexed only by a single bidentate (e.g., TMEDA) or by two monodentate (e.g., THF or Et20) ligands. In such cases [(69), (71), (72), (75)-(78), and (81)—(83) ], the lithium centers are only three coordinate. Electronic factors in the anion [notably, B N multiple bonding in (75)—(78) ] also may reduce the charge density at N, and lower the ability to bridge two...

Photoelectron spectroscopy (PES) has been shown to provide a convenient probe of metal ion effective nuclear charge and the nature of the metal-ligand bond via the energy of valence-electron photoionizations (16, 20, 22, 284, 285, 312, 332-334). Recently, PES spectroscopy has been employed in the study of oxo-molybdenum compounds of the type (L-A5)MoE(X,Y) [E = O, S, NO X, Y = halide, alkoxide, or thiolate] in order to evaluate the synergy between the axial (E) and equatorial (X,Y) donors in affecting the ionization energy of the HOMO localized on the Mo center (16, 284, 334). These studies have conclusively shown that equatorial dithiolene coordination electronically bulfers the Mo center in (L-A pMoEttdt) (Fig. 13) from the severe electronic perturbations associated with the enormous variation in the Ji-donor/acceptor properties... 

X-rays are scattered predominantly by electrons rather than atomic nuclei. To determine atomic coordinates, electron densities are therefore assumed to be concentrated spherically around individual nuclei. This assumption ignores all possible effects that chemical bonding may have on electronic density in molecules. Such a hypothetical array of spherical atoms located at the nuclear positions of an actual molecule in a crystal is known as a promolecule. Molecular structures determined by routine crystallographic methods are invariably the structures of promolecules. 

Water plays multiple roles in biological electron transfer (ET) energy bath, polarizable medium that defines the reaction coordinate, electronic coupling bridge, and intimate participant in molecular recognition. This article explores these many faces of water in ET. Links are drawn to reactions in photosynthesis, oxidative phosphorylation, proton-coupled ET, and DNA damage and repair. 

Selective epoxidation of olefins by vanadium(V) alkyl peroxo complexes has also been reported (76). These complexes are very effective stereo-selective reagents for the transformation of olefins into epoxides. The mechanism consists of binding of the olefin to the metal to displace one of the peroxo-oxygen atoms, nucleophilic attack of the bound oxygen atom on the coordinated electron-deficient olefin, dissociation of the epoxide, and reaction of the remaining vanadium intermediate with... 

Figure 5. Schematic variation in the electron potential energy as a function of the nuclear coordinates (qa and qp for the reactant and product systems, respectively) and of the electron coordinate, (a) Forbidden electron transfer (b) allowed electron transfer (c) projection of the system trajectory on the electron coordinate-nuclear coordinates plane, q and qp are the values of the nuclear coordinate at the equilibrium for the reactant or product systems, respectively, and q that at the transition state. Solid lines, variations of the nuclear coordinates ( ->) electron tunneling.

However, it should be noted that, for U02 S04 1, the most eharacteristie eoordination of sulfate ions relative to the uranyl ions is not bidentate bridging (B, Fig. 10) but tridentate bridging (T, Fig. 10). Due to the inelusion of third O atom into the coordination, electron-donor ability of sulfate ions increases significantly they have El= 3Ei = 6.3e. For this reason, the most stable electroneutral complexes have the composition [U02(S04)(H20)2], since for them Ne = 7.8 + 6.3 + 2-1.9 = 17.9 e and ANe = 0.1 e i.e. less than for the complexes XIX. This explains why the [U02(S04)(H20)2] complexes occur in crystal structures more frequently than the [U02(S04)(H20)3] complexes. 

Figure 5. Time-dependence of the transformation in 25-A CdSe crystals at 463 K at different pressmes. (A) The forward transition at A 5.2 GPa, 5.7 GPa, 0 6.9 GPa. (B) The reverse transition at 0 0.7 GPa, 1.0 GPa, A1.2 GPa. (1 GPa s 10,000 atm) The abscissa is the intensity of the four-coordinate electronic absorption feature. Fits are single-exponential decays. Rate constants were obtained from the slope of the fitted lines, and are equivalent to relaxation times (= In 2/k) in the forward transition of A 21 min, 3.6 min, 0 20 s. In the reverse transition 0 24 min, 0 3.8 min, and A 16 s. Each crystal in the ensemble transforms instantaneously relative to the experiment time such that the relaxation is a measure of the average time required to overcome the kinetic barrier. Once a nanocrystal transforms to the stable stmcture, it is statistically unlikely that it will fluctuate back unless the pressure is changed accordingly, because the transition is measured far from equilibrium. [Used by permission of the editor of Science, from Jacobs et al (2001), Fig. 2.]...

R. A. Michelin, E. Pizzo, A. Scarso, P. Sgarbossa, G. Strukul, A. Tassan, Baeyer-Villiger oxidation of ketones catalyzed by platinum(II) Lewis acid complexes containing coordinated electron-poor fluorinated diphosphines, Organometallics 24 (2005) 1012. 

For an octahedral complex the jr-bonding leads in the (d2sp3) hybridization model to an increase in the number of electrons in the group of d orbitals which may be treated by Slater s rules, as well as to an increase of electrons in the next outer shell. As it is probable that the jr-coordinated electrons may not be completely assigned to the transition metal ion, and as the more accurate tables of Clementi 108> contain only values for neutral atoms, the resulting effect can... 

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