Revisiting the role of octahedral symmetry in the interpretation of spectroscopic properties of [OsF6]2- and PtF6 complexes.

The electronic structure of [OsF6]2- and PtF6 complexes was studied by means of CASSCF/NEVPT2 multiconfigurational calculations, including spin-orbital coupling, which is very relevant in the case of these metals. From these calculations, it is possible to establish that in the octahedral symmetry (Oh), the ground state is non-magnetic (Jeff = 0) because of the strong ligand field, and the interaction with paramagnetic excited states is almost negligible, resulting in a non-magnetic behavior, which is in agreement with the experimental evidence.

Mobile genetic elements drive the multidrug resistance and spread of Salmonella serotypes along a poultry meat production line.

The presence of mobile genetic elements in Salmonella isolated from a chicken farm constitutes a potential risk for the appearance of emerging bacteria present in the food industry. These elements contribute to increased pathogenicity and antimicrobial resistance through genes that are related to the formation of biofilms and resistance genes contained in plasmids, integrons, and transposons. One hundred and thirty-three Salmonella isolates from different stages of the production line, such as feed manufacturing, hatchery, broiler farm, poultry farm, and slaughterhouse, were identified, serotyped and sequenced. The most predominant serotype was Salmonella Infantis. Phylogenetic analyses demonstrated that the diversity and spread of strains in the pipeline are serotype-independent, and that isolates belonging to the same serotype are very closely related genetically. On the other hand, Salmonella Infantis isolates carried the pESI IncFIB plasmid harboring a wide variety of resistance genes, all linked to mobile genetic elements, and among carriers of these plasmids, the antibiograms showed differences in resistance profiles and this linked to a variety in plasmid structure, similarly observed in the diversity of Salmonella Heidelberg isolates carrying the IncI1-Iα plasmid. Mobile genetic elements encoding resistance and virulence genes also contributed to the differences in gene content. Antibiotic resistance genotypes were matched closely by the resistance phenotypes, with high frequency of tetracycline, aminoglycosides, and cephalosporins resistance. In conclusion, the contamination in the poultry industry is described throughout the entire production line, with mobile genetic elements leading to multi-drug resistant bacteria, thus promoting survival when challenged with various antimicrobial compounds.

Genetic Characterization of Salmonella Infantis with Multiple Drug Resistance Profiles Isolated from a Poultry-Farm in Chile.

Salmonella comprises over 2500 serotypes and foodborne contamination associated with this pathogen remains an important health concern worldwide. During the last decade, a shift in serotype prevalence has occurred as traditionally less prevalent serotypes are increasing in frequency of infections, especially those related to poultry meat contamination. S. Infantis is one of the major emerging serotypes, and these strains commonly display antimicrobial resistance and can persist despite cleaning protocols. Thus, this work aimed to isolate S. Infantis strains from a poultry meat farm in Santiago, Chile and to characterize genetic variations present in them. We determined their genomic and phenotypic profiles at different points along the production line. The results indicate that the strains encompass 853 polymorphic sites (core-SNPs) with isolates differing from one another by 0-347 core SNPs, suggesting variation among them; however, we found discrete correlations with the source of the sample in the production line. Furthermore, the pan-genome was composed of 4854 total gene clusters of which 2618 (53.9%) corresponds to the core-genome and only 181 (3.7%) are unique genes (those present in one particular strain). This preliminary analysis will enrich the surveillance of Salmonella, yet further studies are required to assess their evolution and phylogeny.

Relativistic effects on the aromaticity of E3M3H3 (E = C-Pb; M = N-Bi) benzene analogues.

The relativistic effects on the aromaticity of a set of benzene analogues, E3M3H3 (E = C-Pb; M = N-Bi) heterocycles, using magnetically induced current density (MICD) and the NICSzz component of the conventional nucleus independent chemical shift (NICS), is hereby examined. The relativistic effects were evaluated by means of four-component relativistic MICD, and two-component NMR relativistic shielding tensor methods. MICD and NICS were also computed in a non-relativistic fashion, to assess the influence of scalar-relativistic and spin-orbit effects. Most of the studied compounds exhibit a net diatropic ring current (aromatic), excluding the nitrogen-containing compounds which are non-aromatic (except for C3N3H3), in agreement with their higher E-N electronegativity difference. Only in the case of bismuth compounds, E3Bi3H3, aromaticity is substantially decreased when relativistic effects are included (mainly due to the spin-orbit contribution). The larger the mass of the system, the larger the magnitude of this change, in line with the expected relativistic effects for heavier elements. The analysis based on the NICSzz computations agrees with that of the MICD, thus supporting both the magnetic behavior and the aromatic character of these compounds.

Spin-orbit effects on magnetically induced current densities in the M5- (M = N,P,As,Sb,Bi,Mc) clusters.

This study reports the spin-orbit effects on the aromaticity of the N5-, P5-, As5-, Sb5-, Bi5-, and Mc5- anionic clusters via the magnetically induced current-density method. All-electron density functional theory (DFT) calculations were carried out using the four-component Dirac-Coulomb (DC) hamiltonian, including scalar and spin-orbit relativistic effects. The magnetic index of aromaticity was calculated by numerical integration over the current flow between two atoms in the pentagonal ring. These values were compared to the spin-free values (spin-orbit coupling switched off), in order to assess the spin-orbit effect on aromaticity. It was found that in the heavy anions, Bi5- and Mc5-, there is a significant influence of the spin-orbit coupling. © 2018 Wiley Periodicals, Inc.

Information on Gas-Phase Diatomic Molecules from Magnetically Induced Current Densities.

Magnetically induced current densities are different for different types of chemical bonds, and may help highlight some of their characteristics and stress their main differences. The present work considers magnetically induced current densities in the bonds of diatomic molecules bonded by covalent bonds as well as the gas phase molecules of 1:1 ionic compounds, comparing the current strength values and visualizing current density maps. The results show clear-cut differences for the different types of bonds (non-polar covalent, polar covalent, and ionic), and can also be related to the extent of the covalent or ionic character of a bond. For ionic compounds, the results also show relevant differences depending on the charges of the ions and on their electron configuration (including significant effects from the presence of d electrons in the outer shell of the ions). The article presents and analyses the results in detail. It is concluded that the magnetically induced current densities contribute to the description and interpretation of chemical bonding in diatomic molecules. © 2017 Wiley Periodicals, Inc.

Relativistic effects on the aromaticity of the halogenated benzenes: C6X6, X = H, F, Cl, Br, I, At.

In this study we report about the relativistic effects on the aromaticity of the six hexahalogenated compounds (C6H6, C6F6, C6Cl6, C6Br6, C6I6 and C6At6), via a magnetically induced current density method. All-electron density functional theory (DFT) calculations were carried out using the four-component Dirac-Coulomb (DC) Hamiltonian, including scalar and spin-orbit (SO) relativistic effects. Fully relativistic values of the magnetically induced ring currents were obtained by numerical integration over the current flow. These values were compared to the spin-free (SO interaction switched off) and non-relativistic values, in order to assess the corresponding contributions to aromaticity. It was found that in C6I6 and C6At6 there is a strong SO influence, in line with the expected relativistic effects of the heavy elements, iodine and astatine.

Structural aspects of two α-dihydrazones displaying a complete survey of intermolecular interactions.

The compounds (2'E,2'E)-2,2'-(propane-1,2-diylidene)bis[1-(2-nitrophenyl)hydrazine], C15H14N6O4, (I), and (2Z,3Z)-ethyl 3-[2-(2-nitrophenyl)hydrazinylidene]-2-[2-(4-nitrophenyl)hydrazinylidene]butanoate tetrahydrofuran hemisolvate, C18H18N6O6·0.5C4H8O, (II), are puzzling outliers deviating from a general synthetic route aimed at the preparation of substituted pyrazoles. Possible reasons for this outcome, which is exceptional in an otherwise firmly established synthetic procedure, are analyzed. Compound (I) is unsolvated, while compound (II) crystallizes with a tetrahydrofuran solvent molecule lying on an inversion centre. The ethoxycarbonyl chain of (II), in turn, appears disordered into two equally populated (50%) moieties. In both structures, a plethora of different commonly occurring weak intermolecular interactions [viz. π(phenyl)...π(phenyl), π(C=N)...π(C=N), π(phenyl)...π(C=N), N-H...O and C-H...O] appear responsible for the crystal stability. Much less common are the short O(nitro)...O(nitro) contacts which are observed in the structure of (I), an example of unusual `electron donor-acceptor' (EDA) interactions.

Revisiting Aromaticity and Chemical Bonding of Fluorinated Benzene Derivatives.

The electron delocalization of benzene (C6H6) and hexafluorobenzene (C6F6) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Šabove the ring center correlates well (R (2)>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6-n)F n , where n=1-5).

On substituted pyrazole derivatives. II. (E)-1-(4-{[1-(4-Fluorophenyl)-3,5-dimethyl-1H-pyrazol-4-yl]diazenyl}phenyl)ethanone and (E)-1-(4-chlorophenyl)-3,5-dimethyl-4-[2-(2-nitrophenyl)diazenyl]-1H-pyrazole.

The molecular structures of (E)-1-(4-{[1-(4-fluorophenyl)-3,5-dimethyl-1H-pyrazol-4-yl]diazenyl}phenyl)ethanone, C19H17FN4O, (III), and (E)-1-(4-chlorophenyl)-3,5-dimethyl-4-[2-(2-nitrophenyl)diazenyl]-1H-pyrazole, C17H14ClN5O2, (IV), prepared by reaction of the corresponding ß-diketohydrazones with substituted arylhydrazines in acid media, are nonplanar, with the planes of the lateral phenyl rings forming dihedral angles with that of the central pyrazole ring varying from 2.71 (7) to 45.22 (7)°. The crystal structures are supported by C-H...O, C-H...π and π-π weak intermolecular interactions together with some unusual trifurcated C-Cl...Cl-C contacts, which are discussed in detail.

New Insights into Re3(µ-Cl)3Cl6 Aromaticity. Evidence of σ- and π-Diatropicity.

We have theoretically evaluated the behavior of the Re3(µ-Cl)3Cl6 cluster under magnetic perturbation, and it clearly shows that the magnetic response within the Re3(µ-Cl)3 plane is highly diatropic in nature. An analysis of both the magnetically induced current density (MICD) and induced magnetic field (B(ind)) allows us to classify this cluster as doubly σ- and also π-aromatic on the magnetic criterion. These findings contradict the classical Re-Re double bond representation and favor a chemical bonding pattern that involves delocalized bonds.

On substituted pyrazole derivatives. I. 3-Methyl-4-[(Z)-2-(4-methylphenyl)hydrazin-1-ylidene]-1-(3-nitrophenyl)-1H-pyrazol-5(4H)-one and 3-methyl-4-[(Z)-2-(4-methylphenyl)hydrazin-1-ylidene]-1-[4-(trifluoromethyl)phenyl]-1H-pyrazol-5(4H)-one.

The title substituted pyrazole derivatives, C17H15N5O3 and C18H15F3N4O, share most of their molecular features, in particular the hydrazinylidene (-HN-N=) rather than the diazene (-N=N-) tautomeric form, and differ only in the substituents (NO2 and CF3) on one of the outer phenyl rings. The molecular units are basically planar, with the rotation of the phenyl rings being hindered by the presence of two intramolecular hydrogen bonds having the keto O atom as acceptor. In both structures, the packing is governed by weak C-H...O, C-H...π and π-π interactions. The subtle way in which minor structural differences lead to rather different supramolecular structures is analysed.

Minimizing the risk of reporting false aromaticity and antiaromaticity in inorganic heterocycles following magnetic criteria.

Although aromaticity is a concept in chemistry, in the last years, special efforts have been carried out in order to propose theoretical strategies to quantify it as a property of molecular rings. Among them, perhaps the computation of nucleus independent chemical shifts (NICSs) is the most commonly used, since it is possible to calculate it in an easy and fast way with most used quantum chemistry software. However, contradicting assignments of aromaticity by NICS and other methods have been reported in the literature, especially in studies concerning inorganic chemistry. In this Article is proposed a new and simple strategy to use the NICS information to assess aromaticity, identifying the point along the axis perpendicular to the molecular plane where the in-plane component of NICS becomes zero; it is called free of in-plane component NICS (FiPC-NICS). This spatial point is proposed as secure to consider NICS as an aromaticity descriptor; this simple proposal is evaluated in borazine and cyclotriphosphazenes. The results are compared with carefully examined aromatic stabilization energies and magnetically induced current-density analysis.

Dimers linked by type-I C-F···F-C contacts in (Z)-3-methyl-4-[2-(4-methylphenyl)hydrazinylidene]-1-(pentafluorophenyl)-1H-pyrazol-5(4H)-one.

The title compound, C17H11F5N4O, is described and compared with two closely related analogues in the literature. There are two independent molecules in the asymmetric unit, linked by N-H···O hydrogen bonds and π-π interactions into dimeric entities, presenting a noticeable noncrystallographic C2 symmetry. These dimers are in turn linked by a medium-strength type-I C-F···F-C interaction into elongated tetramers. Much weaker C-H···F contacts link the tetramers into broad two-dimensional substructures parallel to (101).

3,5-Dimethyl-4-[(E)-(2-nitrophenyl)diazenyl]-1-(2,3,4,5,6-pentafluorophenyl)-1H-pyrazole.

The title compound, C(17)H(10)F(5)N(5)O(2), is described and compared with its 4-nitrophenyl isomer [Bustos, Sánchez, Schott, Alvarez-Thon & Fuentealba (2007). Acta Cryst. E63, o1138-o1139]. The title molecule presents its nitro group split into two rotationally disordered components, which in conjunction with the rotation of the `unclamped' rings constitute the main molecular differences. Packing is directed by a head-to-tail type `I' C-F...F-C interaction, generating double-chain strips running along [100]. These substructures are interlinked by a variety of weak F...F, O...F, F...π and O...π interactions.

(Z)-1-(2-Chloro-phen-yl)-3-methyl-4-[2-(4-nitro-phen-yl)hydrazin-1-yl-idene]-1H-pyrazol-5(4H)-one.

There are two independent mol-ecules, A and B, in the asymmetric unit of the title compound, C(16)H(12)ClN(5)O(3). The relative orientations of the chloro-phenyl ring with respect to the pyrazole ring in the two crystallographically independent mol-ecules are different, and their corresponding dihedral angles are -53.3 (2) and 114.09 (18)° in mol-ecules A and B, respectively. There are two strong intramolecular N-H⋯O hydrogen bonds, and two weak intramolecular C-H⋯O and C-H⋯Cl hydrogen bonds. The crystal packing is constructed by weak C-H⋯O and N-H⋯O inter-actions, and two π-π stacking inter-actions [centroid-centroid distances = 3.7894 (9) and 3.5719 (10) Å], forming a mol-ecular ladder along the a axis.

(E)-3,5-Dimethyl-1-p-tolyl-4-(p-tolyl-diazen-yl)-1H-pyrazole.

There are two independent mol-ecules, A and B, in the asymmetric unit of the title compound, C(19)H(20)N(4), in each of which the N=N double bond has an E conformation. The dihedral angles between the pyrazole ring and the p-tolyl rings in the 1- and 4-positions are 22.54 (8) and 35.73 (7)°, respectively, in mol-ecule A. The corresponding dihedral angles in mol-ecule B are 28.13 (8) and 22.18 (8)°. In the crystal, the A and B mol-ecules are linked by weak C-H⋯π inter-actions, leading to inversion dimers in each case.

2-[2-(4-Acetyl-phen-yl)hydrazinyl-idene]-1,3-diphenyl-propane-1,3-dione.

In the title compound, C(23)H(18)N(2)O(3), the inter-planar angle between the benzoyl units is 80.51 (6)° while the dihedral angles between the hydrazinyl-idene and benzoyl groups are 43.43 (6) and 54.16 (6)°. In the crystal, a strong resonance-assisted intra-molecular N-H⋯O hydrogen bond is observed. The mol-ecules form an inversion dimer via a pair of weak C-H⋯O hydrogen bonds and a π-π inter-action [centroid-centroid distance of 3.5719 (10) Å]. These dimers are linked via weak C-H⋯O contacts, forming chains along the b axis.

Probing the aromaticity of the [(H(t)Ac)3(µ2-H)6], [(H(t)Th)3(µ2-H)6],(+), and [(H(t)Pa)3(µ2-H)6] clusters.

In this study we report about the aromaticity of the prototypical [(H(t)Ac)(3)(µ(2)-H)(6)], [(H(t)Th)(3)(µ(2)-H)(6)](+), and [(H(t)Pa)(3)(µ(2)-H)(6)] clusters via two magnetic criteria: nucleus-independent chemical shifts (NICS) and the magnetically induced current density. All-electron density functional theory calculations were carried out using the two-component zeroth-order regular approach and the four-component Dirac-Coulomb Hamiltonian, including scalar and spin-orbit relativistic effects. Four-component current density maps and the integration of induced ring-current susceptibilities clearly show that the clusters [(H(t)Ac)(3)(µ(2)-H)(6)] and [(H(t)Th)(3)(µ(2)-H)(6)](+) are non-aromatic whereas [(H(t)Pa)(3)(µ(2)-H)(6)] is anti-aromatic. However, for the thorium cluster we find a discrepancy between the current density plots and the classification through the NICS index. Our results also demonstrate the increasing influence of f orbitals, on bonding and magnetic properties, with increasing atomic number in these clusters. We think that the enhanced electron mobility in [(H(t)Pa)(3)(µ(2)-H)(6)] is due the significant 5f character of its valence shell. Also the participation of f orbitals in bonding is the reason why the protactinium cluster has the shortest bond lengths of the three clusters. This study provides another example showing that the magnetically induced current density approach can give more reliable results than the NICS index.

2-[2-(4-Nitro-phen-yl)hydrazinyl-idene]-1,3-diphenyl-propane-1,3-dione.

In the mol-ecular structure of the title compound, C(21)H(15)N(3)O(4), the inter-planar angle between the benzoyl units is 89.7 (1)°. The corresponding angles between the phenyl-hydrazono and the benzoyl groups are 31.4 (3) and 60.8 (2)°, respectively. In the crystal, a strong resonance-assisted intra-molecular hydrogen bond (N-H⋯O) and a weak intra-molecular hydrogen bond (C-H⋯N) strongly affect the observed conformation of the mol-ecule. The crystal packing is determined by a strong inter-molecular hydrogen bond (N-H⋯O), giving rise to a helical chain along the a axis. In addition, two weak inter-molecular contacts (C-H⋯O) are observed.