Understanding Chemical Selectivity through Well Selected Excited States.

In this publication, we propose a new set of reactivity/selectivity descriptors, derived within a Rayleigh-Schrödinger perturbation theory framework, for chemical systems undergoing an electrostatic (point-charge) perturbation. From the electron density polarization at first order, qualitative insight on reactivity is retrieved, while more quantitative information (noteworthy selectivity) can be obtained from either the second-order energy response or the number of shifted electrons under perturbation. Noteworthily, only a small number of excitations contribute significantly to the overall responses to perturbation, suggesting chemical reactivity could be foreseen by a careful scrutiny of the electron density reorganization upon excitation.

Comment on "Revisiting the definition of local hardness and hardness kernel" by C. A. Polanco-Ramirez, M. Franco-Pérez, J. Carmona-Espíndola, J. L. Gázquez and P. W. Ayers, Phys. Chem. Chem. Phys., 2017, 19, 12355.

In a recent article Polanco-Ramirez et al. proposed new definitions of local chemical potential and local hardness starting from the first derivative of the energy with respect to the number of electrons and a smart use of the chain rule. In this comment we show that this derivation appears naturally in the Taylor expansion of the energy, showing that the construction of Polanco-Ramirez et al. is not artificially built.

A comparison of experimental and DFT calculations of ¹95Pt NMR shielding trends for [PtX(n)Y(6-n)](2-) (X, Y = Cl, Br, F and I) anions.

A comparison between experimental and calculated gas-phase as well as the conductor-like screening model DFT (195)Pt chemical shifts of a series of octahedral [PtX(6-n)Y(n)](2-) complexes for X = Cl, Br, F, I was carried out to assess the accuracy of computed NMR shielding and to gain insight into the dominant σ(dia), σ(para) and σ(SO) shielding contributions. The discrepancies between the experimental and the DFT-calculated (195)Pt chemical shifts vary for these complexes as a function of the coordinated halide ions, the largest being obtained for the fluorido-chlorido and fluorido-bromido complexes, while negligible discrepancies are found for the [PtCl(6-n)Br(n)](2-) series; the discrepancies are somewhat larger where a significant deviation from the ideal octahedral symmetry such as for the geometric cis/trans or fac/mer isomers of [PtF(6-n)Cl(n)](2-) and [PtF(6-n)Br(n)](2-) may be expected. The discrepancies generally increase in the order [PtCl(6-n)Br(n)](2-) < [PtBr(6-n)I(n)](2-) < [PtCl(6-n)I(n)](2-) < [PtF(6-n)Br(n)](2-) ≈ [PtF(6-n)Cl(n)](2-), and show a striking correlation with the increase in electronegativity difference Δχ between the two halide ligands (X(-) and Y(-)) bound to Pt(IV) for these anions: 0.09 < 0.52 < 0.63 < 1.36 ≈ 1.27, respectively. The computed (195)Pt sensitivity to Pt-X bond displacement, ∂(δ(195)Pt)/∂(ΔPt-X), of these complexes is very large and depends on the halide ion, decreasing from 24 800, 18 300, 15 700 to 12 000 ppm/Å for [PtF(6)](2-), [PtCl(6)](2-), [PtBr(6)](2-) and [PtI(6)](2-), respectively.

DFT study of isomers of the ruthenium dihydride complex RuH2(CO)2(AsMe2Ph)2.

A density functional theory (DFT) study of cct-As, ccc, and cct-CO isomers of the ruthenium dihydride complex RuH2(CO)2(AsMe2Ph)2 is reported (see Scheme for the labeling isomer 34 structures of RuH2(CO)2(AsMe2Ph)2). Complex geometries and relative energies of different isomers have been calculated with both B3LYP and M06-2X functionals. The results show that the B3LYP calculated Boltzmann populations of cct-As, ccc, and cct-CO isomers are 65.5, 34.2, and 0.3%, respectively. These are in better agreement with the experimental data than those calculated at the M06-2X level. However, the calculations of 1H NMR chemical shifts were found to be better described with M06-2X than with B3LYP or with HF level of theories. In addition, a transition state between the two most stable isomers was determined through DFT/(B3LYP or M06-2X) calculations. Graphical Abstract Scheme: Labeling structure of RuH2(CO)2(AsMe2Ph)2.

Acute aquatic toxicity of organic solvents modeled by QSARs.

To limit in vivo experiments, the use of quantitative structure-activity relationships (QSARs) is advocated by REACH regulation to predict the required fish, invertebrate, and algae EC50 for chemical registration. The aim of this work was to develop reliable QSARs in order to model both invertebrate and algae EC50 for organic solvents, regardless of the mechanism of toxic action involved. EC50 represents the concentration producing the 50 % immobilization of invertebrates or the 50 % growth inhibition of algae. The dataset was composed of 122 organic solvents chemically heterogeneous which were characterized by their invertebrate and/or algae EC50. These solvents were described by physico-chemical descriptors and quantum theoretical parameters calculated via density functional theory. QSAR models were developed by multiple linear regression using the ordinary least squares method and descriptor selection was performed by the Kubinyi function. Invertebrate EC50 was well-described with LogP, dielectric constant, surface tension, and minimal atomic Mulliken charges while algae EC50 of organic solvents (except amines) was predicted with LogP and LUMO energy. To evaluate robustness and predictive performance of the QSARs developed, several strategies have been used to select solvent training sets (random, EC50-based selection and a space-filling design) and both internal and external validations were performed.

Simulation of electron energy loss near-edge structure at the Al and N K edges and Al L(23) edge in cubic aluminium nitride.

Calculations of electron energy near edge structures (ELNES) are compared with experimental data obtained in a high-resolution transmission electron microscope. This study concerns small precipitates of aluminium nitride in low carbon steel. The ELNES technique allows to clearly establish that these precipitates crystallize in a cubic rather than in a hexagonal crystallographic cell. The influence on simulated spectra of different parameters are investigated: the size of the atomic shell and its relation with the electron inelastic mean free path. We also examine the influence of the core hole and the sensitivity to cell parameters. We particularly examine the Al L(23) near edge structure and features relating to the different transition channels (A(1g), E(g) and T(2g)). Results of a multiple scattering and band structure calculations using ICXANES and WIEN97 codes, respectively, are compared in the region from 0 to 30 eV above the edge onsets. Both calculations are in a rather good agreement.

Quantitative structure-activity relationship to predict acute fish toxicity of organic solvents.

REACH regulation requires ecotoxicological data to characterize industrial chemicals. To limit in vivo testing, Quantitative Structure-Activity Relationships (QSARs) are advocated to predict toxicity of a molecule. In this context, the topic of this work was to develop a reliable QSAR explaining the experimental acute toxicity of organic solvents for fish trophic level. Toxicity was expressed as log(LC50), the concentration in mmol.L(-1) producing the 50% death of fish. The 141 chemically heterogeneous solvents of the dataset were described by physico-chemical descriptors and quantum theoretical parameters calculated via Density Functional Theory. The best subsets of solvent descriptors for LC50 prediction were chosen both through the Kubinyi function associated with Enhanced Replacement Method and a stepwise forward multiple linear regressions. The 4-parameters selected in the model were the octanol-water partition coefficient, LUMO energy, dielectric constant and surface tension. The predictive power and robustness of the QSAR developed were assessed by internal and external validations. Several techniques for training sets selection were evaluated: a random selection, a LC50-based selection, a balanced selection in terms of toxic and non-toxic solvents, a solvent profile-based selection with a space filling technique and a D-optimality onions-based selection. A comparison with fish LC50 predicted by ECOSAR model validated for neutral organics confirmed the interest of the QSAR developed for the prediction of organic solvent aquatic toxicity regardless of the mechanism of toxic action involved.

Effect of self-interaction error in the evaluation of the bond length alternation in trans-polyacetylene using density-functional theory.

The calculation of the bond-length alternation (BLA) in trans-polyacetylene has been chosen as benchmark to emphasize the effect of the self-interaction error within density-functional theory (DFT). In particular, the BLA of increasingly long acetylene oligomers has been computed using the Møller-Plesset wave-function method truncated at the second order and several DFT models. While local-density approximation (LDA) or generalized gradient corrected (GGA) functionals strongly underestimate the BLA, approaches including self-interaction corrections (SIC) provide significant improvements. Indeed, the simple averaged-density SIC scheme (ADSIC), recently proposed by Legrand et al. [J. Phys. B 35, 1115 (2002)], provides better results for the structure of large oligomers than the more complex approach of Krieger et al. [Phys. Rev. A 45, 101 (1992)]. The ADSIC method is particularly promising since both the exchange-correlation energy and potential are improved with respect to standard LDA/GGA using a physically appealing correction, through a different route than the more popular approach through the Hartree-Fock exchange inclusion within the hybrid functionals.

Photochemistry of the CpNiNO complex. A theoretical study using density functional theory.

The photochemistry of the CpNiNO complex has been investigated using density functional theory. The whole potential energy curve along the NiNO angle coordinate is presented for the first time with both ground and metastable states, and transition states connecting the minima. The excited states of the GS, MS(I), and MS(II) species have been calculated using time-dependent density functional theory. Furthermore, the structure of the excited states pertaining to the photochemistry of CpNiNO has been optimized. From these results it is shown that the backward GS <-- MS(II) <-- MS(I) reaction is more efficient than the forward GS --> MS(II) --> MS(I) scheme.

Understanding the formation of new clusters of alkali and alkaline Earth metals: a new synthetic approach, single-crystal structures, and theoretical calculations.

A new synthetic approach, reacting alkaline earth metal iodides with butyllithium, lithium hydroxide, and/or lithium butoxide under salt elimination, is presented, giving access to some interesting clusters of calcium, strontium, and barium, partially in combination with lithium. The so far largest calcium cluster Li[[Ca(7)(mu(3)-OH)(8)I(6)(thf)(12)](2)(mu(2)-I)].3THF, 4, and the new strontium compound [Sr(3)I(3)(OH)(2)(thf)(9)]I, 5, are shown to feature common building blocks of OH-capped M(3) triangles. On the basis of mainly electrostatic interactions, these clusters are not volatile. By introducing LiO(t)Bu, the two clusters [IM(O(t)Bu)(4)[Li(thf)](4)(OH)] (6, M = Sr; 7, M = Ba) are prepared, 7 exhibiting volatility as an important physical property, which makes it a potential precursor for chemical vapor deposition. The structural relationship between 4, 5, 6, and 7 and their respective starting materials is shown, and possible reaction mechanisms are proposed. Exhibiting surprising and new structural motifs, the bonding modes of these clusters are investigated by the electron localization function as well as by ab initio calculations.