Unraveling the Origin of the Relative Stabilities of Group 14 M2N22+ (M, N = C, Si, Ge, Sn, and Pb) Isomer Clusters

Adaptive σ-Aromaticity in an Unsaturated Three-Membered Ring

Based on Hückel's and Baird's rules, species are aromatic either in the lowest singlet state (S₀ ) or the lowest triplet state (T₁ ) only. Thus, species with adaptive aromaticity (with aromaticity in both the S₀ and T₁ states) is particularly rare. On the other hand, σ-aromaticity in the T₁ state has been underdeveloped, let alone adaptive σ-aromaticity. Herein, via various aromaticity indices including NICS, ACID and EDDB, we demonstrate adaptive σ-aromaticity in an unsaturated three-membered ring, which is a traditional area dominated by π-aromaticity. The origin of adaptive σ-aromaticity could be attributed to the excitation mode of the T₁ state formed from out-of-plane π molecular orbital to the π* orbitals. Thus the σ-aromaticity of the three-membered ring in the S₀ state could hold in the T₁ state. Our findings extend the concept of adaptive σ-aromaticity into three-membered rings and could be useful to further develop the concept of both σ-aromaticity and adaptive aromaticity.

The Peculiar Role of the Au3 Unit in Aum Clusters: σ-Aromaticity of the Au5Zn+ Ion

The stability of small Au_m (m = 4-7) clusters is investigated by analyzing their energetic, geometric, vibrational, magnetic, and electron density properties. Gold clusters can be constructed from stable cyclic 3-center-2-electron (3c-2e) Au₃⁺ units (3-rings) with σ-aromaticity. The stabilization requires a flow of negative charge from internal 3-rings with electron-deficient bonding to peripheral 3-ring units with stronger Au-Au bonds. The valence-isoelectronic clusters Au₆ and Au₅Zn⁺ have similar electronic properties: Au₅Zn⁺ is a strongly σ-aromatic molecule. An understanding of the structure of Au_m clusters is obtained by deriving a Clar's Rule equivalent for polycyclic gold clusters: The structure with the larger number of rings with dominant 3c-2e character and a smaller degree of 3c-3e character occupies the global minimum of the Au_m potential energy surface.

Octahedral aromaticity in 2S+1A1g X6q clusters (X = Li–C and Be–Si, S = 0–3, and q = −2 to +4)

Octahedral aromaticity was found in most clusters of formula X₆^q (X = Li–C and Be–Si) with q = −2 to +4 and spin states ranging from the singlet to the septet that have electronic configurations of closed-shells or open shells half-filled with the same spin electrons.

Planar vs. three-dimensional X62−, X2Y42−, and X3Y32− (X, Y = B, Al, Ga) metal clusters: an analysis of their relative energies through the turn-upside-down approach

Despite the fact that B and Al belong to the same group 13 elements, the B₆²⁻ cluster prefers the planar D_2h geometry, whereas Al₆²⁻ favours the O_h structure, which is caused by orbital interactions.

σ Aromaticity Dominates in the Unsaturated Three-Membered Ring of Cyclopropametallapentalenes from Groups 7-9: A DFT Study

Aromaticity, an old but still fantastic topic, has long attracted considerable interest of chemists. Generally, π aromaticity is described by π-electron delocalization in closed circuits of unsaturated compounds whereas σ-electron delocalization in saturated rings leads to σ aromaticity. Interestingly, our recent study shows that σ aromaticity can be dominating in an unsaturated three-membered ring (3MR) of cyclopropaosmapentalene. An interesting question is raised: Can the σ aromaticity, which is dominant in the unsaturated 3MR, be extended to other cyclopropametallapentalenes? If so, how could the metal centers, ligands, and substituents affect the σ aromaticity? Here, we report a thorough theoretical study on these issues. The nucleus-independent chemical shift calculations and the anisotropy of the current-induced density plots reveal the dominant σ aromaticity in these unsaturated 3MRs. In addition, our calculations show that substituents on the 3MRs have significant effects on the σ aromaticity, whereas the ligand effect is particularly small.

In vitro and in silico evaluation of twelve newly-synthesized 1-acetamide-5-methoxy-2-oxindoles as 5-Ht₇ receptor ligands

Based on in vitro studies of twelve newly-synthesized 1-acetamide-5-methoxy-2-oxindoles as 5-Ht7 receptor ligands, Structure Affinity Relationship (SAR) and Quantitative Structure Affinity Relationship model (QSAR) are provided. Also, a ligand-based pharmacophore model is proposed through molecular docking techniques and Nucleus Independent Chemical Shift DFT calculations (NICS).