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The carbonyl cluster compound [GeRu6(CO)18HI] is unique in regard to its structure and bonding with a GeRu6 cluster core, a planar GeRu4HI unit, extensive multi‐center bonding, and an aromatic ring current similar to benzene (9‐10 nA T−1). The open‐shell cluster core is a Ge‐centered five‐membered Ru4(Ru2) ring with CO ligands and an additional H and I atom, each bridging two Ru atoms on opposite sides of the cluster core. The compound is prepared at 130 °C in a weakly‐coordinating ionic liquid. [ABSTRACT FROM AUTHOR]

The effects of monosubstitution on the aromaticity of benzene are assessed using a number of different quantitative schemes. The ability of the mobile π-electrons to respond to an external magnetic field is evaluated using several variants of the NICS scheme which calculate the shielding of points along the axis perpendicular to the molecule. Another class of measures is related to the drive toward the uniformity of C-C bond lengths and strengths. Several energetic quantities are devised to approximate an aromatic stabilization energy and the tendency of the molecule to maintain planarity. There is a lack of consistency in that the various measures of aromaticity lead to differing conclusions as to the effects of substituents on the aromaticity of the ring. [ABSTRACT FROM AUTHOR]

The stability of soil organic matter (SOM) that governs soil organic carbon (SOC) storage depends on its characteristics and components, but little is known about how tree species in forest ecosystems affect SOM components and characteristics. In this study, we used FTIR spectroscopy to investigate plantations of two ecologically and economically significant tree species—namely, spruce (Picea spp.) and sycamore (Acer pseudoplatanus)—in order to determine how the different litter inputs and root-microbe interactions of these two plantations affect the functional groups, components, and characteristics of their SOM. Soil samples were taken from the topsoil (0–10 cm) and subsoil (10–20 cm). In the 0–10 cm soil depth, the SOM's hydrophilic, hydrophobic, and aromatic components differ between the spruce and sycamore plantations. The hydrophobic components constitute the primary constituents of the SOM of the two forest plantations, in contrast to the expected predominance of the hydrophilic component of the SOM. Also, the high hydrophobicity (hydrophilic/hydrophobic) in the subsoil of the spruce plantations was attributed to a decrease in hydrophilic components and a subsequent increase in hydrophobic components of the SOM. The sycamore plantations exhibited a higher SOM aromaticity and a greater degree of decomposition than the spruce plantations. The aforementioned distinctions emphasise the contrasting mechanisms involved in transforming and turnover of the two-tree species' soil organic matter (SOM). [ABSTRACT FROM AUTHOR]

A series of 5-alkoxy-1,3-benzenedicarbaldehydes and related dimers were prepared in three steps from dimethyl 5-hydroxyisophthalate. Acid catalyzed condensation of the dialdehydes with a tripyrrane dicarboxylic acid, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, afforded good yields of 3-alkoxybenziporphyrins, although dimeric tetraaldehydes failed to give isolatable porphyrinoid products. Proton NMR spectroscopy gave no indication of an aromatic ring current, but addition of trifluoroacetic acid resulted in the formation of dications that exhibited weakly diatropic characteristics. Spectroscopic titration with TFA demonstrated that stepwise protonation took place, generating monocationic and dicationic species. 3-Alkoxybenziporphyrins reacted with nickel(II) or palladium(II) acetate to give the related nickel(II) or palladium(II) complexes. These stable organometallic derivatives showed increased diatropic properties that were most pronounced for the palladium(II) complexes. These unique porphyrinoids provide further insights into the properties of benziporphyrins. [ABSTRACT FROM AUTHOR]

In this work, we have observed that some chiral boron clusters ( B 16 − , B 20 − , B 24 − , and B 28 − ) can simultaneously have helical molecular orbitals and helical spin densities; these seem to be the first compounds discovered to have this intriguing property. We show that chiral Jahn–Teller distortion of quasi-planar boron clusters drives the formation of the helical molecular spin densities in these clusters and show that elongation/enhancement in helical molecular orbitals can be achieved by simply adding more building blocks via a linker. Aromaticity of these boron clusters is discussed. Chiral boron clusters may find potential applications in spintronics, such as molecular magnets. [ABSTRACT FROM AUTHOR]

We have developed novel polynomials called delta polynomials, which are, in turn, derived from the characteristic and matching polynomials of graphs associated with polycyclic aromatic compounds. Natural logarithmic aromatic indices are derived from these delta polynomials, which are shown to provide new insights into the aromaticity of polycyclic aromatic compounds, including the highly symmetric C60 buckminsterfullerene, several other fullerenes, graphene, kekulene series and other cycloarenes, such as polycyclic circumcoronaphenes and coronoids. The newly developed aromatic index yields a value of 6.77 for graphene, 6.516865 for buckminsterfullerene C60(Ih), 5.914023 for kekulene (D6h symmetry), 6.064420 for coronene (D6h), 6.137828 for circumcoronene (D6h), 6.069668 for dicronylene and so forth. Hence, the novel scaled logarithmic aromatic delta indices developed here appear to provide good quantitative measures of aromaticity, especially when they are used in conjunction with other aromatic indicators. [ABSTRACT FROM AUTHOR]

First synthesized in 1868, alizarin became one of the first synthetic dyes and was widely used as a red dye in the textile industry, making it more affordable and readily available than the traditional red dyes derived from natural sources. Despite extensive both experimental and computational analyses on the electronic effects of substituents on the shape of the visible spectrum of alizarin and alizarin Red S, no previous systematic work has been undertaken with the aim to fine tune the dominant absorption region defining its color by introducing other electron‐withdrawing or electron‐donor groups. For such, we have performed a comprehensive study of electronic effects of substituents in position C3 of alizarin by means of a time dependent DFT approach. These auxochromes attached to the chromophore are proven to alter both the wavelength and intensity of absorption. It is shown that the introduction of an electron‐donor group in alizarin causes the transition bands to be significantly red‐shifted whereas electron‐withdrawing groups cause a minor blue‐shifting. [ABSTRACT FROM AUTHOR]

Planar tetracoordinate silicon, germanium, tin, and lead (ptSi/Ge/Sn/Pb) species are scarce and exotic. Here, we report a series of penta-atomic ptSi/Ge/Sn/Pb XB2Bi2 (X = Si, Ge, Sn, Pb) clusters with 20 valence electrons (VEs). Ternary XB2Bi2 (X = Si, Ge, Sn, Pb) clusters possess beautiful fan-shaped structures, with a Bi–B–B–Bi chain surrounding the central X core. The unbiased density functional theory (DFT) searches and high-level CCSD(T) calculations reveal that these ptSi/Ge/Sn/Pb species are the global minima on their potential energy surfaces. Born–Oppenheimer molecular dynamics (BOMD) simulations indicate that XB2Bi2 (X = Si, Ge, Sn, Pb) clusters are robust. Bonding analyses indicate that 20 VEs are perfect for the ptX XB2Bi2 (X = Si, Ge, Sn, Pb): two lone pairs of Bi atoms; one 5c–2e π, and three σ bonds (two Bi–X 2c–2e and one B–X–B 3c–2e bonds) between the ligands and X atom; three 2c–2e σ bonds and one delocalized 4c–2e π bond between the ligands. The ptSi/Ge/Sn/Pb XB2Bi2 (X = Si, Ge, Sn, Pb) clusters possess 2π/2σ double aromaticity, according to the (4n + 2) Hückel rule. [ABSTRACT FROM AUTHOR]

The aromatic character of silolyl and germolyl anions markedly depends on the substituents in the 2,5-positions; carbon-substituted derivatives are nonaromatic, whereas silyl-substituted ones tend to exhibit an aromatic character. However, only carbon-substituted derivatives have been reported for stannolyl anions. In this study, we present the synthesis and structure of a 2,5-disilylated stannolyl anion. Transmetalation of a 2,5-disilyl-1-zirconacyclopentadiene with SnCl4 gave a dichlorostannole 1, which reacted with potassium tris(trimethylsilyl)silanide to introduce a bulky silyl group on the tin atom. Reduction of the 1-chloro-1-silylstannole 2 with lithium generated the lithium salt of the desired stannolyl anion 3 that adopts an η1-coordination to the lithium atom. We concluded that the stannolyl anion 3 is nonaromatic based on the pyramidalized tin center and the C–C bond alternation in the five-membered ring as well as the NMR properties. [ABSTRACT FROM AUTHOR]

We theoretically investigated the nitrogen substitution effect on the molecular structure and π-electron delocalization in linear nitrogen-substituted polycyclic aromatic hydrocarbons (N-PAHs). Based on the optimized molecular structures and magnetic field-induced parameters of fused bi- and tricyclic linear N-PAHs, we found that the local π-electron delocalization of subcycles (e.g., mono- and bicyclic constituent moieties) in linear N-PAHs is preserved, despite deviation from ideal structures of parent monocycles. The introduction of a fused five-membered ring with a pyrrolic N atom (N-5MR) in linear N-PAHs significantly perturbs the π-electronic condition of the neighboring fused six-membered ring (6MR). Monocyclic pyrrole exhibits substantial bond length alternations, strongly influencing the π-electronic systems of both the fused N-5MR and 6MR in linear N-PAHs, depending on the location of shared covalent bonds. A fused six-membered ring with a graphitic N atom in an indolizine moiety cannot generate monocyclic π-electron delocalization but instead contributes to the formation of polycyclic π-electron delocalization. This is evidenced by bifurcated diatropic ring currents induced by an external magnetic field. In conclusion, the satisfaction of Hückel's 4n + 2 rule for both mono- and polycycles is crucial for understanding the overall π-electron delocalization. It is crucial to consider the unique characteristics of the three types of substituted N atoms and the spatial arrangement of 5MR and 6MR in N-PAHs. [ABSTRACT FROM AUTHOR]

Much experimental work has been contributed to all-metal σ, π and δ-aromaticity among transition metals, semimetallics and other metals in the past two decades. Before our focused investigations on the properties of triangular and sandwich-shaped all-metal aromatics, A. I. Boldyrev presented general discussions on the concepts of all-metal σ-aromaticity and σ-antiaromaticity for metallo-clusters. Schleyer illustrated that Nucleus-Independent Chemical Shifts (NICS) were among the most authoritative criteria for aromaticity. Ugalde discussed the earlier developments of all-metal aromatic compounds with all possible shapes. Besides the theoretical predictions, many stable all-metal aromatic trinuclear clusters have been isolated as the metallic analogues of either the σ-aromatic molecule's [H3]+ ion or the π-aromatic molecule's [C3H3]+ ion. Different from Hoffman's opinion on all-metal aromaticity, triangular all-metal aromatics were found to hold great potential in applications in coordination chemistry, catalysis, and material science. Triangular all-metal aromatics, which were theoretically proved to conform to the Hückel (4n + 2) rule and possess the smallest aromatic ring, could also play roles as stable ligands during the formation of all-metal sandwiches. The triangular and sandwich-shaped all-metal aromatics have not yet been specifically summarized despite their diversity of existence, puissant developments and various interesting applications. These findings are different from the public opinion that all-metal aromatics would be limited to further applications due to their overstated difficulties in synthesis and uncertain stabilities. Our review will specifically focus on the summarization of theoretical predictions, feasible syntheses and isolations, and multiple applications of triangular and sandwich shaped all-metal aromatics. The appropriateness and necessities of this review will emphasize and disseminate their importance and applications forcefully and in a timely manner. [ABSTRACT FROM AUTHOR]

The electron density depletion associated with π -hole at the ring center typical of energetic compounds was clearly revealed by the molecular electrostatic potential (ESP). In addition, the spatial arrangement of NO 2 groups appears to affect the ESP value in the ring center, and therefore sensitivity to detonation. Indeed, for monocyclic nitrobenzene compounds with the same number of NO 2 groups, the ESP value in the ring center decreases as the NO 2 groups are more closely spaced. As expected, the central rings become less aromatic as NO 2 groups are added. The MCI, PDI, PLR, NICS z z (1), FLU indices are all strongly correlated with the ESP values observed in the ring center of the set of nitrobenzenes. Aromaticity indices based on electron delocalization criteria appear to be very sensitive to small variations in aromaticity. Among magnetic-based indices, only NICS z z (1) is capable to predict small changes in aromaticity. The PLR index derived from conceptual DFT is quite relevant for predicting small variations in aromaticity. According to our results, the most suitable aromaticity index is not based on a single criterion, and that selecting it is more subtle. Therefore, it is important to combine information from several criteria to obtain a more complete description of the aromaticity of the studied compounds. [Display omitted] • Spatial arrangements of NO 2 groups affect the ESP value at the ring center. • ESP value at the ring center decreases as the NO 2 groups are closely spaced. • Central rings become less aromatic as NO 2 groups are added. • NICS z z (1) is capable of properly predicting small changes in aromaticity. • Delocalization-based indices are sensitive to slight changes in aromaticity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyester polyols of varying aromaticity were synthesized and characterized. • Polyisocyanurate foams were prepared with the different polyester polyols. • Increasing polyol aromaticity slows down foaming kinetics. • Polyol aromaticity does not improve the fire resistance of PIR foams. • Oxygen content of the polyol improves the fire resistance of PIR foams. Polyisocyanurate foams are high-performance thermal insulation materials widely used in the building industry. They combine low thermal conductivity with good fire resistance, thanks to the presence of isocyanurate structures. The impact of the chemical structure of their main building block, polyester polyols, has however rarely been the topic of a systematic investigation. In this work, a series of polyester polyols was synthesized from phthalic anhydride and various diols, resulting in polyols having a constant hydroxyl index but varying levels of aromaticity. Their viscosity and glass transition temperature were found to increase with the aromaticity. The polyols were then used to synthesize rigid polyisocyanurate foams for thermal insulation, to evidence the impact of aromaticity on the properties and fire resistance of the foams. Increasing the polyol aromaticity limits the molecular mobility, which results in slower foaming reaction times. The differences in reactivity between the polyols also lead to foams with slightly different isocyanurate contents, although they were all synthesized with a constant NCO/OH ratio. The main foam properties (morphology, mechanical properties or thermal conductivity) were mostly unaffected by the polyol aromaticity. The aromaticity was not found to improve the fire behavior of the foams, as evidenced by mass loss cone experiments. However, other factors, such as the isocyanurate content of the foams and the oxygen content of the polyols were found to positively influence the fire resistance. It should be related to a higher propensity to form a dense char layer on top of the material, limiting its degradation during the combustion. [ABSTRACT FROM AUTHOR]

La doped silica aerogel composites (La 2 O 3 /SiO 2 -n) with different Si/La molar ratio were synthesized through sol-gel method and atmospheric drying technology, which were used to adsorb thiophenic compounds from model fuels. Compared with the pure SiO 2 aerogel, the adsorption capacities of La 2 O 3 /SiO 2 -n obviously increased, owing to adding La species led to the appearance of the weak Lewis acid sites on the surface. The adsorption mechanism of La 2 O 3 /SiO 2 -n for thiophenics included the direct S-La bond and weak π-La acid-base interaction between La3+ and thiophenics, and the former was primary. Among La 2 O 3 /SiO 2 -n, the La 2 O 3 /SiO 2 -200 not only had the highest adsorption capacity for thiophene, up to 8.16 mg S/g ads (i.e., 138.31 mg-S/mmol La), but also exhibited an excellent anti-aromatics competitive adsorption ability and a good regeneration performance. The adsorption kinetic and adsorption isotherms were well described by pseudo-second-order (PSO) and Langmuir models, respectively, indicating the adsorption of La 2 O 3 /SiO 2 -200 for TH was dominated by chemisorption, which was a spontaneous and endothermic process. The present of aromatics in model fuels had a slightly negative effect on the adsorption of La 2 O 3 /SiO 2 for thiophene. [Display omitted] • Simple preparation of La 2 O 3 /SiO 2 aerogel composites. • Appearance of weak Lewis acid centers on the surface of aerogel after doping La. • The selective adsorption of La 2 O 3 /SiO 2 for thiophenics rather than aromatics. • The main adsorption mechanism was S-La bond instead of π-La acid-base interaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • B21C7 with fewer aromatic substituents shows stronger interaction with Cs+ compared to DB21C7. • Solvent effects more significantly impact the thermodynamic stability of Cs+·B21C7 than Cs+·DB21C7. • Dibenzo CE exhibits faster coordination kinetics with Cs+ ions than monobenzo CE. Aromatic substituent plays a pivotal role in determining the electronic characteristics and coordination capabilities of aromatic crown ethers (CE). In this study, we focus on two types of aromatic CEs: benzo-21-crown-7 (B21C7) and dibenzo-21-crown-7 (DB21C7). Employing isochemical shielding surface (ICSS ZZ) analysis for the first time, we investigate their aromaticity. The thermodynamic properties of their complexes with cesium are calculated using the double-hybrid functional PWPB95-D3, incorporating precise dispersion description. Interactions and conformations are examined through 1D and 2D NMR methods, and coordination dynamics are elucidated via molecular dynamics (MD) simulations. The ESP extreme value of B21C7 is lower than that of DB21C7, indicating stronger electrostatic attraction with Cs+. Solvent effects exert adverse influences on thermodynamic stability, leading to decreased binding Gibbs free energy (|Δ G |) and coordination number (CN) in chloroform compared to the gas phase. Interestingly, the stability of Cs+·B21C7 decreases more than that of Cs+·DB21C7. From a dynamic perspective, an increase in the number of aromatic substituents enhances the structural rigidity of the cavity, facilitating the formation of Cs+·DB21C7. This study establishes a connection between substituent and coordination, offering valuable insights for developing aromatic CEs with high-affinity binding capabilities for metal cations. [ABSTRACT FROM AUTHOR]

photoelectron spectra, electronic structure, anti-aromaticity. [Display omitted] • Electronic structures of pentalene and derivatives. • Simulated UV photoelectron spectra pentalene and derivatives in the gas phase. • Determination of bandgaps in pentalene derivatives. • Study of substituent effects annulation on aromaticity/anti-aromaticity. The vertical, valence ionization energies for pentalene (C 8 H 6) and some of its derivatives have been calculated as free molecules in the gas phase using high-level ab initio coupled-cluster method: EOM-DLPNO-CCSD. Their valence electronic structures depend on the number, type and position of substituents. We have used the calculated vertical, valence ionization energies to simulate UV photoelectron spectra. HOMO-LUMO gaps and the influence of substituents on ionization energies and electronic structure were also studied. We discuss the antiaromaticity and bis-annulation effects in pentalenes. [ABSTRACT FROM AUTHOR]