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A dense artificial neural network, ESE-ΔH-DNN, with two hidden layers for calculating both solvation free energies ΔG°solv and enthalpies ΔH°solv for neutral solutes in organic solvents is proposed. The input features are generalized-Born-type monatomic and pair electrostatic terms, the molecular volume, and atomic surface areas of the solute, as well as five easily available properties of the solvent. ESE-ΔH-DNN is quite accurate for ΔG°solv, with an RMSE (root mean square error) below 0.6 kcal/mol and an MAE (mean absolute error) well below 0.4 kcal/mol. It performs particularly well for alkane, aromatic, ester, and ketone solvents. ESE-ΔH-DNN also exhibits a fairly good accuracy for ΔH°solv prediction, with an RMSE below 1 kcal/mol and an MAE of about 0.6 kcal/mol. [ABSTRACT FROM AUTHOR]

ESE‐EE (Easy Solvation Estimation with Electronegativity equalization) is a quick method for estimation of solvation‐free energies ΔGºsolv, which uses a thoroughly fitted electronegativity equalization (EE) scheme to obtain atomic charges, which are further employed in a scaled noniterative COSMO‐like calculation to evaluate the electrostatic component of ΔGºsolv. Nonelectrostatic corrections including adjustable parameters are also added. For neutral solutes, ESE‐EE yields a mean absolute error (MAE) in ΔGsolv° of 1.5 kcal/mol for aqueous solutions; 1.0 kcal/mol for nonaqueous polar protic solvents; 0.9 kcal/mol for polar aprotic solvents; and about 0.6 kcal/mol for nonpolar solvents. Since ESE‐EE only requires a molecular geometry as input for a ΔGºsolv prediction, it can be utilized for a rapid screening of ΔGºsolvfor large neutral molecules. However, for ionic solutes, ESE‐EE yields larger errors (typically several kcal/mol) and is recommendable for preliminary estimations only. Upon a special refitting, ESE‐EE is able to yield partition coefficients with a good accuracy. [ABSTRACT FROM AUTHOR]

Reactions of silicon and germanium dichlorides L⋅ECl2 (E=Si, L=IPr; E=Ge, L=dioxane) with the phosphinoamidinato‐supported disilylene ({κ2(N,P)‐NNP}Si)2 resulted in formal tetrylene insertions into the Si−Si bond. In the case of the reaction with silylene, two products were isolated. The first product ({κ2(N,P)‐NNP}Si)2SiCl2, is the formal product of direct SiCl2 insertion into the Si−Si bond of ({κ2(N,P)‐NNP}Si)2 and thus features two separated silylamido silylene centers. Over time, migration of the SiCl2 group to a lateral position afforded the second product, the disilylene {κ2(Si,P)−SiCl2NNP}Si−Si{κ2(N,P)‐NNP}. In contrast, insertion of GeCl2 resulted only in the isolation of the germanium analogue of {κ2(Si,P)−SiCl2NNP}Si−Si{κ2(N,P)‐NNP}, containing a Ge atom in the central position namely, compound {κ2(Si,P)−SiCl2NNP}Ge−Si{κ2(N,P)‐NNP}, which is a rare example of a silylene‐germylene. Finally, reaction of disilylene ({κ2(N,P)−NNP}Si)2 with SiCl4 and SiHCl3 led to the formation of the new bis(silyl)silylene, ({NNP}SiCl2)2Si:. All four new products from these insertion reactions have been characterized by multinuclear NMR and single‐crystal X‐ray diffraction studies. [ABSTRACT FROM AUTHOR]

A study of the stable structures of neutral (V2O5)(sub n) clusters (n = 1-5, 8, 10, and 12) using density functional calculations is presented and comparison is made with the calculations for the periodic structure of solid V2O5. The results show that the structures of (V2O5)(sub n) gas-phase clusters is different from the layer structure of the solid bulk as instead of a 6-fold coordination in the crystal structure vanadium tends to adopt a 4-fold coordination with one terminal V=O and three bridging V-O bonds in the gas phase clusters.

The structures of vanadium oxide anions and the respective neutral species are determined. Comparison is made with the corresponding neutral systems, and the vertical detachment energies of the anions and the adiabatic electron affinities of the neutrals are calculated.

The synthesis, structure and bonding of AlX and GaX fragments bonded to transition metals are examined in detail. An analysis of the electronic structure was performed using the natural bond orbital method and the topological analysis of the electron density distribution to gain insight into the M-E bonding situation of the molecules. The M-E interaction is characterized as strong donor-acceptor bonds with significant ionic contributions.

In the present paper we discuss and compare two different energy decomposition schemes: Mayer’s Hartree–Fock energy decomposition into diatomic and monoatomic contributions [Chem. Phys. Lett. 382, 265 (2003)], and the Ziegler–Rauk dissociation energy decomposition [Inorg. Chem. 18, 1558 (1979)]. The Ziegler–Rauk scheme is based on a separation of a molecule into fragments, while Mayer’s scheme can be used in the cases where a fragmentation of the system in clearly separable parts is not possible. In the Mayer scheme, the density of a free atom is deformed to give the one-atom Mulliken density that subsequently interacts to give rise to the diatomic interaction energy. We give a detailed analysis of the diatomic energy contributions in the Mayer scheme and a close look onto the one-atom Mulliken densities. The Mulliken density ρA has a single large maximum around the nuclear position of the atom A, but exhibits slightly negative values in the vicinity of neighboring atoms. The main connecting point between both analysis schemes is the electrostatic energy. Both decomposition schemes utilize the same electrostatic energy expression, but differ in how fragment densities are defined. In the Mayer scheme, the electrostatic component originates from the interaction of the Mulliken densities, while in the Ziegler–Rauk scheme, the undisturbed fragment densities interact. The values of the electrostatic energy resulting from the two schemes differ significantly but typically have the same order of magnitude. Both methods are useful and complementary since Mayer’s decomposition focuses on the energy of the finally formed molecule, whereas the Ziegler–Rauk scheme describes the bond formation starting from undeformed fragment densities. [ABSTRACT FROM AUTHOR]

The present work provides a generalization of Mayer’s energy decomposition for the density-functional theory (DFT) case. It is shown that one- and two-atom Hartree–Fock energy components in Mayer’s approach can be represented as an action of a one-atom potential VA on a one-atom density ρA or ρB. To treat the exchange-correlation term in the DFT energy expression in a similar way, the exchange-correlation energy density per electron is expanded into a linear combination of basis functions. Calculations carried out for a number of density functionals demonstrate that the DFT and Hartree–Fock two-atom energies agree to a reasonable extent with each other. The two-atom energies for strong covalent bonds are within the range of typical bond dissociation energies and are therefore a convenient computational tool for assessment of individual bond strength in polyatomic molecules. For nonspecific nonbonding interactions, the two-atom energies are low. They can be either repulsive or slightly attractive, but the DFT results more frequently yield small attractive values compared to the Hartree–Fock case. The hydrogen bond in the water dimer is calculated to be between the strong covalent and nonbonding interactions on the energy scale. [ABSTRACT FROM AUTHOR]

Hydrosilylation of carbonyls catalyzed by 2 has gone through intermediate formation of cationic silane [sigma]-complexes 4 that have undergone nucleophilic abstraction of the silylium cation studied by DFT calculations.

Silane S-H activation on Cp([Pr.sub.2.sup.i]MeP)FeH has proceeded differently from the conventionally postulated Si-H oxidative addition or silane [sigma]-complexation. This has involved the interaction between the silyl and metal-bound hydride, resulting in a structure with novel H...Si[R.sub.3]...H bonding.

A multistep mechanism for the reaction of a model complex (Cp)(sub 3)Ru3H5 with C5H6 is proposed on the basis of a density functional (B3LYP) exploration of the mechanism. The reactivity of the triruthenium complex is characterized as versatile and cooperative by the direct involvement of all three metal centers and two cluster hydrides.

The treatment of cyclic thioureas with the aluminum(I) compound NacNacAl ( 1; NacNac=[ArNC(Me)CHC(Me)NAr]−, Ar=2,6-Pri2C6H3) resulted in oxidative cleavage of the C=S bond and the formation of 3 and 5, the first monomeric aluminum complexes with an Al=S double bond stabilized by N-heterocyclic carbenes. Compound 1 also reacted with triphenylphosphine sulfide in a similar manner, which resulted in cleavage of the P=S bond and production of the adduct [NacNacAl=S(S=PPh3)] ( 8). The Al=S double bond in 3 can react with phenyl isothiocyanate to furnish the cycloaddition product 9 and zwitterion 10 as a result of coupling between the liberated carbene and PhN=C=S. All novel complexes were characterized by multinuclear NMR spectroscopy, and the structures of 5, 9, and 10 were confirmed by X-ray diffraction analysis. The nature of the Al=S bond in 5 was also probed by DFT calculations. [ABSTRACT FROM AUTHOR]