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Polycyclic aromatic hydrocarbons (PAHs) are widely recognized as catalysts for interstellar H2 formation. Extensive exploration into the catalytic potential of various PAHs has encompassed both theoretical investigations and experimental studies. In the present study, we focused on studying the reactivity of an imperfect aromatic molecule, indene (C9H8), and its hydrogenated counterpart, indane (C9H10), as potential catalysts for H2 formation within the interstellar medium. The reactions of these molecules with H atoms at 3.1 K were investigated experimentally using the para-H2 matrix isolation technique. Our experimental results demonstrate that both indene and indane are reactive toward H atoms. Indene can participate in H-atom-abstraction and H-atom-addition reactions, whereas indane primarily undergoes H-atom-abstraction reactions. The H-atom-abstraction reaction of indene results in the formation of the 1-indenyl radical (R1) (C9H7) and H2 molecule. Simultaneously, an H-atom-addition reaction forms the 1,2-dihydro-indene-3-yl radical (R2) (C9H9). Experiments also reveal that the H-atom-abstraction reaction of indane also produces the R2 radical. To the best of our knowledge, this study represents the first reporting of the infrared spectra of R1 and R2 radicals. The experimental results, combined with theoretical findings, suggest that indane and indene may play a role in the catalytic formation of interstellar H2. Furthermore, these results imply a quasi-equilibrium between the investigated molecules and the formed radicals via H-atom-addition and H-atom-abstraction reactions. [ABSTRACT FROM AUTHOR]

Realization of planar tetracoordinate arrangements of nitrogen atoms is challenging because their preference for localized bonding (caused by its high electronegativity) makes them typically tricoordinate. This is especially true for the more electronegative oxygen atoms. Herein, we computationally designed two clusters NBe4H4− and OBe4H4; they contain a planar tetracoordinate nitrogen (ptN) and planar tetracoordinate oxygen (ptO) atom, respectively. Remarkably, the former is a dynamically stable global minimum, while the latter is not. The bonding analysis proves that planar tetracoordination in NBe4H4− favors over tricoordination because of the presence of multicenter delocalized bonds. In contrast, the planar tricoordination dominates due to its weak delocalized bonding ability of oxygen in the OBe4H4 cluster. Moreover, the 6σ/2π double aromaticity due to multicenter delocalized bonds allows the NBe4H4− cluster to obtain additional stability. This cluster is a promising synthetic due its dynamic and thermodynamic stability. [ABSTRACT FROM AUTHOR]

Intramolecular hydrogen bonding (IHB) interactions were considered in XC5H3HC = Y···HO molecules which include OH···Y unit (Y = O, S and NH) and heteroatom X (X = N, P, As and Sb). Alteration of heteroatoms X in para position causes a change of properties of electron charge densities on these molecules and influences on strength of the IHB interactions. The aromaticity of the ring A (involving IHB interaction) and ring B (involving heteroatoms X) of XC5H3HC = Y···HO molecules was calculated using para-delocalisation index (PDI). Results reveal that the change of X from N to Sb is followed by the decrease in aromaticity of the mentioned rings. However, the strength of the IHB interactions increases during the change of X. Moreover, IHB energies were estimated using some computational methods and a viewpoint based on the properties of ring critical points (RCPs). The IHB energies obtained using a viewpoint based on the properties of RCPs have a better relationship with hydrogen bonding descriptors. Also, intermolecular hydrogen bond (HB) interactions of hydrogen peroxide with the close and open forms of the XC5H3HC = Y···HO molecules were considered. Cooperative effects of the HB and IHB interactions are revealed. Moreover, energy decomposition analysis (EDA) highlights the role of exchange interactions on the stability of the XC5H3HC = Y···HO···H2O2 complexes. [ABSTRACT FROM AUTHOR]

We have calculated the magnetically induced current density susceptibility for gold-containing organometallic molecular rings using the gauge-including magnetically induced currents (GIMIC) method. The aromatic nature has been determined by calculating the strength of the magnetically induced ring current susceptibility, which is often called ring current. To our knowledge, we show here for the first time that gold-containing organometallic rings may be aromatic or antiaromatic sustaining ring currents in the presence of an external magnetic field. The calculated aromatic character of the rings agrees with the aromatic nature one expects when using Hückel's aromaticity rules. The studied auracycles and diauracycles with 4n electrons in the conjugated orbitals generally sustain a weak paratropic ring current, whereas those having 4n + 2 electrons in the conjugated orbitals sustain a diatropic ring current that is almost as strong as that of benzene. The number of electrons are obtained by assuming that each C, N and Au atom of the ring contribute one electron, and a H atom connected to a N atom in the ring increases the number of electrons by one. An electron-attracting ligand at Au removes one electron from the ring. Formation of a short Au–Au bonding diauracycles reduces the number of electrons in the ring by two. [ABSTRACT FROM AUTHOR]

We examine the aromaticity of four benzoborepin isomers using magnetic, geometric, and delocalization criteria. We observe a trend in which the six-membered ring (6MR) exhibits higher aromaticity for isomers 1 and 2, while the seven-membered ring (7MR) exhibits a more pronounced aromatic character in isomers 3 and 4. Our CCSD(T)-level calculations demonstrate that isomers 1 and 2 are more stable (in that order), consistent with their higher aromaticity than isomers 3 and 4. The results of the three criteria mentioned above show a preference for forming the 6MR over the 7MR in the more stable isomers. Additionally, the 6MR in 1 shows a higher aromaticity when compared to 2 which explains its greater stability. For this reason, we conclude that the Glidewell–Lloyd rule governs aromaticity and relative stability in benzoborepines. [ABSTRACT FROM AUTHOR]

Herein we report a square-like D4h H©K4H4− anion with one planar tetracoordinate hydrogen (ptH) center, which is the global minimum (GM) structure and possesses good dynamic stability. The planar structure of the system is preserved by four peripheral K–H–K three-center two-electron (3c-2e) σ bonds together with one 5c-2e σ bond over the HK4 core. The multicenter ionic bonds dominate the stability of ptH, while the contribution of qualitative σ aromaticity is extremely limited. [ABSTRACT FROM AUTHOR]

Electron delocalization and aromaticity was comparatively evaluated in recently synthesized figure‐eight molecules made of two condensed U‐shaped polycyclic aromatic hydrocarbon moieties connected either by two single bonds or by two para‐phenylene groups. The selected examples include molecules that incorporate eight‐membered and sixteen‐membered rings, as well as a doubly [5]helicene‐bridged (1,4)cyclophane. We probe whether some electron delocalization could occur through the stereogenic single bonds in these molecules: Is aromaticity purely (semi‐)local, or possibly also global in these molecules? It was concluded that the situation can go from a purely (semi‐)local character when the dihedral angle at the connecting single bonds is large, such as in biphenyl, to a predominantly (semi‐)local character with a minor global contribution when the dihedral angle is small, such as in the para‐phenylene connectors of the [5] helicene‐bridged cyclophane. [ABSTRACT FROM AUTHOR]

Inverse sandwich complexes of Yb and Sm stabilized by a bulky β‐diketiminate (BDI) ligand have been prepared: (BDI)Ln(η6,η6‐C6H6)Ln(BDI); Ln=lanthanide. Coordinated benzene ligands can be neutral, di‐anionic or, often controversially discussed, even tetra‐anionic. The formal charge on benzene is correlated to assignment of the metal oxidation state which generally poses a problem. Herein, we take advantage of the structural similarities found when comparing CaII with YbII, and SrII with SmII complexes. In this work, we found an excellent overlap of the Ca/Yb inverse sandwich structures but a striking difference for the Sr/Sm pair. The much shorter Sm−N and Sm‐C6H6 distances are strong evidence for a SmIII‐benzene−4‐SmIII assignment. This was further supported by NMR spectroscopy, magnetic susceptibility, reactivity and comprehensive computational investigation. [ABSTRACT FROM AUTHOR]

We disclose an indenoannulated tridecacyclene comprising a central cyclooctatetraene moiety with multiple adjacent pentagonal rings which is accessible in a concise synthetic sequence. The saddle‐shaped geometry of the non‐benzenoid polycyclic scaffold and its unique packing behavior in the solid state were characterized by X‐ray crystallography. In electrochemical studies, the compound undergoes seven reversible redox events comprising five reductions and two oxidations. The dicationic and dianionic species obtained by chemical oxidation and reduction, respectively, were characterized spectroscopically in solution. Density functional theory calculations were applied to provide insights into aromaticity evolution in the respective charged species, highlighting the beneficial effect of the non‐benzenoid moieties on charge stabilization [ABSTRACT FROM AUTHOR]

Inverse sandwich complexes of Yb and Sm stabilized by a bulky β‐diketiminate (BDI) ligand have been prepared: (BDI)Ln(η6,η6‐C6H6)Ln(BDI); Ln=lanthanide. Coordinated benzene ligands can be neutral, di‐anionic or, often controversially discussed, even tetra‐anionic. The formal charge on benzene is correlated to assignment of the metal oxidation state which generally poses a problem. Herein, we take advantage of the structural similarities found when comparing CaII with YbII, and SrII with SmII complexes. In this work, we found an excellent overlap of the Ca/Yb inverse sandwich structures but a striking difference for the Sr/Sm pair. The much shorter Sm−N and Sm‐C6H6 distances are strong evidence for a SmIII‐benzene−4‐SmIII assignment. This was further supported by NMR spectroscopy, magnetic susceptibility, reactivity and comprehensive computational investigation. [ABSTRACT FROM AUTHOR]

Perchlorinated vanadyl tetrapyrazinoporphyrazine and its reduced form obtained by reduction by potassium graphite in the presence of cryptand in o-dichlorobenzene have been synthetized. The reaction leads to the formation of a crystalline anionic salt cryptand(K+)2[(TPyzPzCl84−)VIVO]2− (1), where reduction is ring-centered and results in [TPyzPzCl84−] tetraanions. This causes a difference between shorter and longer bond lengths of 0.078 Å, disrupting macrocycle aromaticity. Reduction of [Cl8TPyzPzVIVO] leads to a strong blue-shift of the Q band (about 100 nm) in both solid state and THF solution. The starting compound is easily reduced to a monoanion, but preparation of the dianionic form requires further study. Magnetic properties of 1 are governed by VIV ions (S = 1/2), while [TPyzPzCl84−] tetraanions are diamagnetic. The EPR spectra of 1 show a strongly anisotropic signal due to the hyperfine interaction of an unpaired electron of VIV with a 51V nucleus (I = 7/2). [ABSTRACT FROM AUTHOR]

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]

This work reports the magnetic index of aromaticity of cyclophosphazene (c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$H6$$ {}_6 $$) and their halogenated cyclic derivatives: c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$F6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$Cl6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$Br6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$I6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$At6$$ {}_6 $$ and c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$Ts6$$ {}_6 $$. This index, also known as ring‐current strength, is calculated by numerical integration of the magnetically‐induced current density vector field which is generated by a perturbing external magnetic field. Due to the presence of heavy X=Br,I,At$$ \mathrm{X}=\mathrm{Br},\mathrm{I},\mathrm{At} $$ atoms in c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$X6$$ {}_6 $$, important relativistic were expected. Accordingly, 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 values were also compared with the corresponding spin‐free (scalar relativistic) ones. [ABSTRACT FROM AUTHOR]

We present herein the synthesis of novel pseudo‐metalla‐carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N‐confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well‐known porphyrins, these species exhibit an unusually narrow HOMO–LUMO gap, resulting in an unprecedentedly low‐energy absorption in the second near‐infrared (NIR‐II) region. Density functional theory (DFT) calculations revealed unique dπ‐pπ‐conjugated electronic structures involving the metal dπ‐ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open‐metal coordination site in the peripheral NN dipyrrin site, forming hetero‐metal complexes (1Pd‐BF2 and 1Pt‐BF2) through boron difluoride complexation. The resulting hetero metalla‐carbaporphyrinoid species displayed further redshifted NIR‐II absorption, highly efficient photothermal conversion efficiencies (η; 62–65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ‐pπ‐conjugated metalla‐aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity‐relevant NIR‐II dyes. [ABSTRACT FROM AUTHOR]

This combined experimental and theoretical study illustrates the profound consequences of non‐planarity on the electronic properties of polycyclic arenes. Three isomeric [10]fibonacene tetraesters were synthesized through a robust and regiocontrolled Perkin/Mallory approach: a nearly planar [10]phenacene derivative, a moderately twisted [10]semicircle derivative, and a 3D non‐planar [10]helicene derivative. The photophysical properties of the 3D [10]helicene isomer were found to be dramatically different from the comparable ones of the [10]phenacene and [10]semicircle isomers. The aromatic properties of the [10]phenacene and [10]semicircle isomers conform well with their predictive Kekulé and Clar analyses, but the [10]helicene isomer deviates from these general topological rules, which appears to be a general phenomenon for [n]fibonacenes with n≥9. [ABSTRACT FROM AUTHOR]

We present herein the synthesis of novel pseudo‐metalla‐carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N‐confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well‐known porphyrins, these species exhibit an unusually narrow HOMO–LUMO gap, resulting in an unprecedentedly low‐energy absorption in the second near‐infrared (NIR‐II) region. Density functional theory (DFT) calculations revealed unique dπ‐pπ‐conjugated electronic structures involving the metal dπ‐ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open‐metal coordination site in the peripheral NN dipyrrin site, forming hetero‐metal complexes (1Pd‐BF2 and 1Pt‐BF2) through boron difluoride complexation. The resulting hetero metalla‐carbaporphyrinoid species displayed further redshifted NIR‐II absorption, highly efficient photothermal conversion efficiencies (η; 62–65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ‐pπ‐conjugated metalla‐aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity‐relevant NIR‐II dyes. [ABSTRACT FROM AUTHOR]

This combined experimental and theoretical study illustrates the profound consequences of non‐planarity on the electronic properties of polycyclic arenes. Three isomeric [10]fibonacene tetraesters were synthesized through a robust and regiocontrolled Perkin/Mallory approach: a nearly planar [10]phenacene derivative, a moderately twisted [10]semicircle derivative, and a 3D non‐planar [10]helicene derivative. The photophysical properties of the 3D [10]helicene isomer were found to be dramatically different from the comparable ones of the [10]phenacene and [10]semicircle isomers. The aromatic properties of the [10]phenacene and [10]semicircle isomers conform well with their predictive Kekulé and Clar analyses, but the [10]helicene isomer deviates from these general topological rules, which appears to be a general phenomenon for [n]fibonacenes with n≥9. [ABSTRACT FROM AUTHOR]

The topological resonance energy (TRE) method was used to investigate the aromaticity of hetero[8]circulenes in both their neutral and doubly charged ion states. The compounds varying stabilities in different charged states were explained in terms of the topological charge stabilization rule. The TRE‐based aromaticity indices were compared with those obtained by the gauge‐including magnetically induced currents (GIMIC) method. However, the lack of correlation between the TRE and GIMIC aromaticity indices, as well as the contradictory trends observed, suggest that further investigation is necessary to fully understand the aromaticity of hetero[8]circulenes. We employed the circuit resonance energy (CRE) method to assess local aromaticity. Our CRE results indicate that individual benzene or heterocyclic five‐membered units within the molecule maintain their strong aromatic character and serve as the primary source of global aromaticity, both in their neutral and doubly charged ion states. Although our CRE results provide valuable insights, it is important to note that there are cases where the magnitude of local aromaticity predicted by the nucleus‐independent chemical shift (NICS[0] and NICS[1]) indices does not align with our CRE results. [ABSTRACT FROM AUTHOR]

In 2023, a themed collection on "Emerging frontiers in aromaticity" was published in Chemical Science. The collection included a Perspective Essay entitled "Aromaticity – Quo Vadis", which presents a wealth of viewpoints on the multiple definitions of aromaticity. The present Prefatory Review revives the viewpoint that aromaticity is a theoretical notion and as such, its meaning is theory dependent. Therefore, when aromaticity is made to correspond to two or more 'experimental' ideas, e.g., energetic, structural, electronic, magnetic, it would be absurd to maintain that aromaticity is explicitly defined by each of these ideas in turn. The Review emphasizes that the descriptor 'theoretical' in general, including in the context of aromaticity does not mean 'computational'. The theoretical notion of aromaticity is illustrated by Craig's rules of aromaticity and by Craig's second type of aromaticity based on symmetry and delocalization in pπ-dπ bonds, recently highlighted as 'Craig-Type Möbius aromaticity'. [ABSTRACT FROM AUTHOR]

Based on extensive global minimum searches augmented with first-principles theory calculations, we predict herein the first boron-based perfect tetrahedral clusters Td B16P4 (2) and Td B16As4 (3) which, as aromatic non-metal analogs of the experimentally observed Td Au20 (2003, Science299, 864), all contain a truncated Td B16 (1) cage at the center effectively stabilized by four trivalent non-metal atoms (P, As) at the corners. Detailed natural bonding orbital (NBO) and adaptive natural density partitioning (AdNDP) bonding analyses indicate that the valences of all the trivalent component atoms in these tetrahedral clusters are fully satisfied, rendering spherical aromaticity and extra stability to the systems. The IR, Raman, and photoelectron spectra (PES) of the concerned species are theoretically simulated to facilitate their characterizations in future experiments. [ABSTRACT FROM AUTHOR]

A series of pentagonal bipyramidal anionic germanium clusters doped with heavy rare earth elements, REGe6− (RE = Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), have been identified at the PBE0/def2‐TZVP level using density functional theory (DFT). Our findings reveal that the centrally doped pentagonal ring structure demonstrates enhanced stability and heightened aromaticity due to its uniform bonding characteristics and a larger charge transfer region. Through natural population analysis and spin density diagrams, we observed a monotonic decrease in the magnetic moment from Gd to Yb. This is attributed to the decreasing number of unpaired electrons in the 4f orbitals of the heavy rare earth atoms. Interestingly, the system doped with Er atoms showed lower stability and anti‐aromaticity, likely due to the involvement of the 4f orbitals in bonding. Conversely, the systems doped with Gd and Tb atoms stood out for their high magnetism and stability, making them potential building blocks for rare earth‐doped semiconductor materials. [ABSTRACT FROM AUTHOR]

Stabilization of hexaphyrin(1.0.1.0.1.0) (named "rosarin") in its 25π radical state is achieved using a hetero‐bimetal‐coordination strategy. The antiaromatic BF2 complex B‐1 was first synthesized, and then rhodium ion was inserted into B‐1 to produce the BF2/Rh(CO)2 mixed complex Rh‐B‐1 as a highly air‐stable radical. The structures of B‐1 and Rh‐B‐1 were determined by single‐crystal X‐ray diffractions, and the antiaromatic or radical character was identified by various spectroscopy evidence and theoretical calculations. Rh‐B‐1 exhibits excellent redox properties, enabling amphoteric aromatic‐antiaromatic conversion to their 24/26π states. Compared to the 24/26π conjugation systems on the same skeleton, Rh‐B‐1 has the narrowest electrochemical and optical band gaps, with the longest absorption band at 1010 nm. The ring‐current analysis reveals intense paratropic currents for B‐1 and co‐existing diatropic‐paratropic currents for Rh‐B‐1. This hetero‐bimetal‐coordination system provides a novel platform for organic radical stabilization on porphyrinoids, showing the prospect of modulating ligand oxidation states through rational coordination design. [ABSTRACT FROM AUTHOR]

The appropriate arrangement of near‐infrared (NIR) chromophores allows for the modification of the peak wavelength in the NIR region and efficient use of NIR light. However, the preparation of novel NIR chromophores using simple procedures remains a formidable challenge. Herein, we report the synthesis of ball‐shaped ruthenium complex oligomers. The metal complexes can be synthesized in a single step and interact strongly with NIR light. Alkyne‐substituted low‐symmetry ball‐shaped ruthenium complexes were synthesized and subjected to Eglinton coupling to obtain dehydro[12] and [18]annulene‐fused dimers and trimers. Fine‐tuning of the reaction conditions led to the selective synthesis of the target oligomers. NMR spectroscopy confirmed that the 18π‐aromatic and 12π‐antiaromatic properties of the annulene influenced the ruthenium complex chromophore, and magnetic circular dichroism spectroscopy showed changes in the electronic structure of their excited state owing to molecular‐symmetry differences. The absorption coefficient in the NIR region of the absorption spectra of the oligomers increased significantly, supporting the efficient use of light by oligomerization. The formation of oligomers using ball‐shaped metal complexes is a simple and effective strategy for controlling NIR optical properties. [ABSTRACT FROM AUTHOR]

Although second near‐infrared (NIR‐II, 1000–1500 nm) light has attracted considerable attention, especially for life sciences applications, the development of organic dyes with NIR‐II absorption remains a formidable challenge. Herein we report the design, synthesis, and electronic properties of 20π‐electron antiaromatic benziphthalocyanines (BPcs) that exhibit intense absorption bands in the NIR region. The strong, low‐energy absorption of the antiaromatic BPcs is attributed to electric‐dipole‐allowed HOMO‐LUMO transitions with narrow band gaps, enabled by the reduced structural symmetry of BPc compared with regular porphyrins and phthalocyanines. The combination of peripheral substituents and a central metal decreases the HOMO‐LUMO energy gaps, leading to the extension of the absorption bands into the NIR‐II region (reaching 1100 nm) under reductive conditions. [ABSTRACT FROM AUTHOR]

In a series of earlier studies, the effect of benzo‐annelation was found to be a useful tool for tuning the aromaticity in polycyclic conjugated compounds to desired level. In this work we studied the (anti)aromaticity of benzo‐annelated derivatives of three conjugated hydrocarbons (anthracene, fluoranthene and biphenylene) in their lowest lying singlet (S0) and triplet (T1) states by means of the energy effect (ef), harmonic oscillator model of aromaticity (HOMA), multicentre delocalization indices (MCI), magnetically induced current densities (MICDs) and nucleus independent chemical shifts (NICS). We showed that benzo‐annelation is a topology‐based effect which can be used to modify the T1 state excitation energies (E(T1)). A quantitative model was established being able to accurately predict the E(T1) based only on the numbers of angularly, linearly and geminally annelated benzene rings. In addition, it was demonstrated that the E(T1) can be directly related to the (anti)aromatic character of the central ring in the studied molecules in their S0 state. [ABSTRACT FROM AUTHOR]

Recently, π–π stacked antiaromatic π‐systems have received considerable attention because they can exhibit stacked‐ring aromaticity due to substantial intermolecular orbital interactions. Here, we report three antiaromatic norcorrole dimers that self‐assemble to form supramolecular architectures through chiral self‐sorting. A 2,2’‐linked norcorrole dimer with 3,5‐di‐tert‐butylphenyl groups forms a π‐stacked dimer both in solid and solution states via homochiral self‐sorting. Its association constant in solution is (3.6±1.7)×105 M−1 at 20 °C. In the solid state, 3,3’‐linked norcorrole dimers with 3,5‐di‐tert‐butylphenyl and phenyl groups afford macrocyclic and helical supramolecular assemblies via heterochiral and homochiral self‐sorting, respectively. Notably, the subtle modification in the substituent resulted in a complete change in the structure of the aggregates and the chiral self‐sorting mode. The present findings demonstrate that structural manipulation in antiaromatic monomer units leads to the formation of various supramolecular assemblies on the basis of the attractive interactions between antiaromatic π‐systems. [ABSTRACT FROM AUTHOR]

Neutral four‐membered rings with 4n electrons are generally Hückel antiaromatic. On the other hand, 4n electron system can also be Möbius aromatic, although identification has escaped so far. A recent study of double Möbius aromaticity has been put forwarded in the D2h symmetric singlet ground state of four member Pa2B2 ring. Although interesting, but the synthesis possesses a significant challenge as Pa is rare, highly radioactive and toxic. Herein, a synthetically viable four membered Rh2B2 cluster is proposed which contains double Möbius aromaticity. Interestingly, the three membered RhB2− cluster also possess Möbius aromaticity and is the smallest ring to show such phenomenon. [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 photophysical properties of a series of recently synthesized single benzene fluorophores were investigated using ensemble density functional theory calculations. The energetic stability of the ground and excited state species were counterposed against the aromaticity index derived from local vibrational modes. It was found that the large Stokes shift of the fluorophores (up to ca. 5800 cm −1) originates from the effect of electron donating and electron withdrawing substituents rather than π‐delocalization and related (anti‐)aromaticity. On the basis of nonadiabatic molecular dynamics simulations, the absence of fluorescence from one of the regioisomers was explained by the occurrence of easily accessible S 1/S 0 conical intersections below the vertical excitation energy level. It is demonstrated in the manuscript that the analysis of local mode force constants and the related aromaticity index represent a useful tool for the characterization of π‐delocalization effects in π‐conjugated compounds. [ABSTRACT FROM AUTHOR]

3,4‐Dimethylenecyclobutene (DMCB) is an unusual isomer of benzene. Motivated by recent synthetic progress to substituted derivatives of this scaffold, we carried out a theoretical and computational analysis with a particular focus on the extent of (anti)aromatic character in the lowest excited states of different multiplicities. We found that the parent DMCB is non‐aromatic in its singlet ground state (S0), lowest triplet state (T1), and lowest singlet excited state (S1), while it is aromatic in its lowest quintet state (Q1) as this state is represented by a triplet multiplicity cyclobutadiene (CBD) ring and two uncoupled same‐spin methylene radicals. Interestingly, the Q1 state, despite having four unpaired electrons, is placed merely 4.8 eV above S0, and there is a corresponding singlet tetraradical 0.16 eV above. The DMCB is potentially a highly useful structural motif for the design of larger molecular entities with interesting optoelectronic properties. Here, we designed macrocycles composed of fused DMCB units, and according to our computations, two of these have low‐lying nonet states (i. e., octaradical states) at energies merely 2.40 and 0.37 eV above their S0 states as a result of local Hückel‐ and Baird‐aromatic character of individual 6π‐ and 4π‐electron monocycles. [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]

We report a synthetic approach to π‐expanded [6]helicenes incorporating tropone and azocine units in combination with a 5‐membered ring, which exhibit intriguing structural, electronic, and chiroptical properties. The regioselective Beckmann rearrangement allows the isolation of helical scaffolds containing 8‐membered lactam, azocine, and amine units. As shown by X‐ray crystallographic analysis, the incorporation of tropone or azocine units leads to highly distorted [6]helicene moieties, with distinct packing motifs in the solid state. The compounds exhibit promising optoelectronic properties with considerable photoluminescence quantum yields and tunable emission wavelengths depending on the relative position of the nitrogen center within the polycyclic framework. Separation of the enantiomers by chiral high‐performance liquid chromatography (HPLC) allowed characterization of their chiroptical properties by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The azocine compounds feature manifold redox chemistry, allowing for the characterization of the corresponding radical anions and cations as well as the dications and dianions, with near‐infrared (NIR) absorption bands extending beyond 3000 nm. Detailed theoretical studies provided insights into the aromaticity evolution upon reduction and oxidation, suggesting that the steric strain prevents the azocine unit from undergoing aromatization, while the indene moiety dominates the observed redox chemistry. [ABSTRACT FROM AUTHOR]

Beyond previously described carbo‐naphthalene and carbo‐biphenyl, a novel type of bis‐carbo‐benzenic molecules is envisaged from the stilbene parent. The synthesis, structure, spectroscopic and electrochemical properties of two such carbo‐stilbenes are described at complementary experimental and computational DFT levels. In the selected targets, the bare skeletal carbo‐mer of carbo‐stilbene is decorated by 8 or 10 phenyl groups, 0 or 2 tert‐butyl groups, and 2 n‐octyl chains, the later substituents being introduced to compensate anticipated solubility issues. As in the parent stilbene series, isomers of the phenylated carbo‐stilbenes are characterized. The cis‐ and trans‐isomers are, however, formed in almost equal amounts and could not be separated by either chromatography or crystallization. Nevertheless, due to a slow interconversion at the NMR time scale (up to 55 °C) the 1H NMR signals of both isomers of the two carbo‐stilbenes could be tentatively assigned. The calculated structure of the cis‐isomer exhibits a helical shape, consistent with the observed magnetic shielding of phenyl p‐CH nuclei residing inside the shielding cone of the facing C18 ring. The presence of the two isomers in solution also gives rise to quite broad UV‐vis absorption spectra with main bands at ca 460, 560 and 710 nm, and a significant bathochromic shift for the decaphenylated carbo‐stilbene vs the di‐tert‐butyl‐octaphenylated counterpart. Square wave voltammograms do not show any resolution of the two isomers, giving a reversible reduction wave at −0.65 or −0.58 V/SCE, and an irreversible oxidation peak at 1.11 V/SCE, those values being classical for most carbo‐benzene derivatives. Calculated NICS values (NICS(1)=−12.5±0.2 ppm) also indicate that the aromatic nature of the C18 rings is not markedly affected by the dialkynylbutatriene (DAB) connector between them. [ABSTRACT FROM AUTHOR]

This work provides a detailed multi‐component analysis of aromaticity in monosubstituted (X = CH3, CH2−, CH2+, NH2, NH−, NH+, OH, O−, and O+) and para‐homodisubstituted (X = CH3, CH2, NH2, NH, OH, and O) benzene derivatives. We investigate the effects of substituents using single‐reference (B3LYP/DFT) and multireference (CASSCF/MRCI) methods, focusing on structural (HOMA), vibrational (AI(vib)), topological (ELFπ), electronic (MCI), magnetic (NICS), and stability (S0–T1 splitting) properties. The findings reveal that appropriate π‐electron‐donating and π‐electron‐accepting substituents with suitable size and symmetry can interact with the π‐system of the ring, significantly influencing π‐electron delocalization. While the charge factor has a minimal impact on π‐electron delocalization, the presence of a pz orbital capable of interacting with the π‐electron delocalization is the primary factor leading to a deviation from the typical aromaticity characteristics observed in benzene. [ABSTRACT FROM AUTHOR]

Evaluating the effects of a solvent on the properties of a solute molecule is important to understand its behavior in a solution of that solvent; this, in turn, is important because most reactions—including all the reactions in biological systems—occur in solution. In its most common definition, aromaticity is a property of molecules with delocalized electrons in a ring. It significantly influences their behavior and, therefore, it is important to evaluate the effects of a solvent on it. The most powerful magnetic criterion to estimate aromaticity considers magnetically induced current densities in the ring. The present work applies this approach to adducts of hydroxybenzenes with explicit water molecules. Hydroxybenzenes are selected as the simplest aromatic systems capable of forming solute–solvent hydrogen bonds with water molecules. Hydroxybenzenes without consecutive OH groups are selected to avoid the influence of intramolecular hydrogen bonds between OHs. Current densities are calculated focusing on the aromatic rings, and the effect of the solvent is highlighted by the density changes caused by the presence of the water molecules attached to the hydroxybenzene molecule. The results show that the strength of the ring current decreases as the number of OH groups in the molecule increases. The strength does not change greatly in the adducts with respect to the isolated molecules: the change extent and direction depend mostly on the arrangement of water molecules around the central molecule. The current density maps show that the water molecules may also be involved in the current flow. [ABSTRACT FROM AUTHOR]

Density functional study (DFT) is performed for understanding the reactivity, aromaticity, and UV-visible absorption spectra of chrysene-based materials. Effect of BN doping on the said parameters are analyzed along with the effect of –Me (methyl), –OH (hydroxyl), –CHO (formyl) –COOH (carboxyl) and –CN (cyano) substituents. Global reactivity parameters viz. energy of HOMO (EHOMO), global hardness (η), chemical potential (μ) and electrophilicity (ω) are computed. Nucleus independent chemical shifts (NICS) values are estimated to study the variation in aromaticity. Time dependent density functional theory (TD-DFT) is used to study the UV–Visible absorption spectra. Effects of BN doping and substituents on corresponding dipole moments and band gaps are also analyzed. Presence of BN unit and/or substituents induced considerable impact on global reactivity, dipole moment, band gap and aromaticity of the chosen systems, especially for BN doped chrysene at the edge. Absorption spectra which are red shifted in presence of BN and substituents are mostly found within the UV-region. [ABSTRACT FROM AUTHOR]

In the overall aromaticity of a molecular system, the magnitude of σ -aromaticity influences the degree of bond length averaging in the molecular geometry, while the magnitude of π -aromaticity reflects the strength of π -electron delocalization, subsequently affecting the electronic transport properties of the entire molecular system. Simultaneously, the aromaticity type of a molecular system is primarily determined by the symmetry of the innermost π molecular orbitals. In this study, we conducted computational simulations of the aromaticity and electronic transport properties of compounds, including C8H8Cu2 with p π – d π delocalization effects and C12H8 with p π – p π delocalization effects, along with their Li derivatives. Based on calculated NICS values, ring current directions, molecular structural configurations and the symmetry of the innermost π molecular orbitals, we clarified the aromaticity types of the molecular systems. Combined with the analysis of molecular electrical conductivity properties, we gained insights into the fundamental attributes of Li-bridge bonds in Li derivatives and the factors influencing electronic transport pathways. Consequently, we established a relationship between the aromaticity of molecular systems and their electronic transport properties. To a certain extent, a novel criterion for evaluating molecular aromaticity is proposed from the perspective of single-molecule electronics. Through the analysis of molecular aromaticity and electrical conductivity, we have clarified that planar Craig-Möbius type π -aromaticity and non-planar Heilbronner-Möbius type σ -aromaticity determine the molecular electron transport capabilities. Additionally, by combining the analysis of bonding types and electron transport pathways, we explain the reason why the C 1 2 H8Li4 molecule, satisfying the 4n electron rule, exhibits Heilbronner-Möbius π -antiaromaticity, which primarily arises from the localization of electrons in its Li-bridged bonds. This research contributes to understanding the fundamental properties of molecular bonding, particularly Li-bridged bonds, and offers a new method for assessing aromaticity from the perspective of single-molecule electronics. [ABSTRACT FROM AUTHOR]

The classical simple picture of stepwise B‐to‐C migratory insertion of all three alkyl groups in the carbonylation reaction of trialkyl boranes with CO was shown not to be correct, except for the first alkyl group shift affording an acyl borane. The second and third direct alkyl shifts turned out to be kinetically hampered due to the non‐activated character of the B−C bond in electron‐poor B atoms. The latter can only be achieved by either the autocatalytic action of the final alkyl boron oxide or by formation of dimeric species with weakened B‐alkyl bonds at borate centres. Both thermodynamic and several NICS‐related parameters pointed to scarce, even "negative", aromatic character for boroxines, the final cyclotrimerization products of alkyl‐boron oxides. [ABSTRACT FROM AUTHOR]

Carbazole‐incorporated smaragdyrin BF2‐complex 3 was synthesized by SNAr reaction of 3,5‐dibromo‐8‐mesityl‐BODIPY 1 with 3,6‐di(tert‐butyl)‐1,8‐di(pyrrol‐2‐yl)carbazole 2 as a nucleophile. Demetalation of 3 with ZrCl4 gave the corresponding smaragdyrin free base 4 in a good yield. Oxidations of 3 and 4 with MnO2 gave smaragdyrins 5 and 6, respectively, both followed by aromaticity switching, since the oxidized products showed a moderate paratropic ring current owing to their 20π‐electronic circuits. Further, treatment of 4 with [RhCl(CO)2]2 in the presence of NaOAc gave RhI complex 7, and oxidation of 3 with RuCl3 in the presence of triethylamine led to the formation of a spiro dimer product, 8. [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]

Norcorrole Ni(II) complexes have recently received considerable attention because they are readily accessible antiaromatic molecules. Their high stability under ambient conditions and ease of synthesis have enabled the exploration of the intrinsic properties of antiaromatic molecules. Here, we report the synthesis and properties of meso–meso singly linked porphyrin‐norcorrole hybrids and a triply linked porphyrin‐norcorrole hybrid. The singly linked and triply linked porphyrin‐norcorrole hybrids were fully characterized, including an X‐ray structural analysis. Due to their orthogonal conformation, the singly linked hybrids maintain the individual electronic properties of their porphyrin and norcorrole subunits, while the triply linked hybrid shows a significantly smaller electrochemical HOMO–LUMO gap (0.45 eV) than that of Ni(II) dimesitylnorcorrole (1.08 eV). Furthermore, the triply linked hybrid exhibits singlet diradical characteristics, as confirmed by VT NMR, ESR, and SQUID experiments. [ABSTRACT FROM AUTHOR]

Norcorrole Ni(II) complexes have recently received considerable attention because they are readily accessible antiaromatic molecules. Their high stability under ambient conditions and ease of synthesis have enabled the exploration of the intrinsic properties of antiaromatic molecules. Here, we report the synthesis and properties of meso–meso singly linked porphyrin‐norcorrole hybrids and a triply linked porphyrin‐norcorrole hybrid. The singly linked and triply linked porphyrin‐norcorrole hybrids were fully characterized, including an X‐ray structural analysis. Due to their orthogonal conformation, the singly linked hybrids maintain the individual electronic properties of their porphyrin and norcorrole subunits, while the triply linked hybrid shows a significantly smaller electrochemical HOMO–LUMO gap (0.45 eV) than that of Ni(II) dimesitylnorcorrole (1.08 eV). Furthermore, the triply linked hybrid exhibits singlet diradical characteristics, as confirmed by VT NMR, ESR, and SQUID experiments. [ABSTRACT FROM AUTHOR]

Analysis of the variations of the off‐nucleus isotropic magnetic shielding, σiso(r), around thiophene, thienothiophenes, dithienothiophenes and sulflowers in their electronic ground (S0) and lowest triplet (T1) states reveals that some of the features of aromaticity and bonding in these molecules do not fit in with predictions based on the popular Hückel's and Baird's rules. Despite having 4n π electrons, the S0 states of the sulflowers are shown to be aromatic, due to the local aromaticities of the individual thiophene rings. To reduce its T1 antiaromaticity, the geometry of thiophene changes considerably between S0 and T1: In addition to losing planarity, the carbon‐carbon two 'double' and one 'single' bonds in S0 turn into two 'single' and one 'double' bonds in T1. Well‐defined Baird‐style aromaticity reversals are observed between the S0 and T1 states of only three of the twelve thiophene‐based compounds investigated in this work, in contrast, the sulflower with six thiophene rings which is weakly aromatic in S0 becomes more aromatic in T1. The results suggest that the change in aromaticity between the S0 and T1 states in longer chains of fused rings is likely to affect mostly the central ring (or the pair of central rings); rings sufficiently far away from the central ring(s) can retain aromatic character. [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]

Carbene and its analogous silylene and germylene ligated trinuclear gold complexes are well established due to their cationic stability, but the anionic stability of such complexes is still rare. Density functional theory calculations on recently synthesized [Au3{C4H4(SiMe3)4Si}3]− and [Au3{C4H4(SiMe3)4Ge}3]− prove that the Au3 core is electron rich and the calculated vertical detachment energy is close to that of halogens. Further proper ligand manipulation on these complexes makes them remarkably stable anions having electron binding energies higher than 5 eV and behaving like superhalogens. Magnetic response calculations based on the magnetically induced current densities and the induced magnetic field confirm the aromatic nature of these anionic Au3-complexes. A study of the gradient Laplacian of electron density and energy density at the bond critical point and electron localization function gives additional bonding information of these anionic complexes. [ABSTRACT FROM AUTHOR]

The study of through‐space electronic coupling in π‐conjugated systems remains an underexplored area. In this work, we present the facile synthesis of two isomeric macrocycles (1 and 2) bridged by [2,2]paracyclophane (pCp) and based on thiophene. The structures of these macrocycles have been confirmed through X‐ray crystallographic analysis. Our investigation centers on their electronic properties across various redox states, with a specific focus on potential through‐space electronic coupling and global aromaticity. Experimental measurements, including UV‐vis‐NIR electronic absorption, NMR, ESR spectra, and X‐ray diffraction, combined with theoretical calculations, reveal that both the neutral compounds and their tetracations exhibit a closed‐shell ground state. However, their dications manifest as diradical dications with a subtle magnetic exchange interaction. Consequently, the through‐space electronic coupling facilitated by the pCp unit in their respective ground states appears to be weak. [ABSTRACT FROM AUTHOR]

Incorporating heteroatoms can effectively modulate the molecular optoelectronic properties. However, the fundamental understanding of BN doping effects in BN‐embedded polycyclic aromatic hydrocarbons (PAHs) is underexplored, lacking rational guidelines to modulate the electronic structures through BN units for advanced materials. Herein, a concise synthesis of novel B2N2‐perylenes with BN doped at the bay area is achieved to systematically explore the doping effect of BN position on the photophysical properties of PAHs. The shift of BN position in B2N2‐perylenes alters the π electron conjugation, aromaticity and molecular rigidness significantly, achieving substantially higher electron transition abilities than those with BN doped in the nodal plane. It is further clarified that BN position dominates the photophysical properties over BN orientation. The revealed guideline here may apply generally to novel BN‐PAHs, and aid the advancement of BN‐PAHs with highly‐emissive performance. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Binary polyantimony clusters, namely [Cu2Sb14]4– and [Ag2Sb14]4–, containing coinage metals, were successfully synthesized and characterized, in which two homoatomic Sb73– subunits are bridged by two coinage metals in η4:η1 and η1:η1 coordination modes, respectively. In [Cu2Sb14]4–, two bridging Cu ions and two Sb atoms form a planar rhombic unit, which was revealed to have antiaromatic properties by theoretical calculations. Further electron structure and bonding analysis confirmed the presence of delocalized bonds in the rhombic unit and the metallophilic interaction between two formal M+ ions. [ABSTRACT FROM AUTHOR]

The exploration of annulene's conformation, electronic properties and aromaticity has generated enduring interest over the years, yet it continues to present formidable challenges for annulenes with more than ten carbon atoms. In this study, we present the synthesis of a stable [10]cyclo‐para‐phenylmethine derivative (1), which bears a resemblance to [10]annulene. 1 can be readily oxidized into its respective cations, wherein electrons are effectively delocalized along the backbone, resulting in different conformations and aromaticity. Both 1 and its tetracation (14+ ⋅ 4SbF6−) exhibit a nearly planar conformation with a rectangular shape, akin to the E,Z,E,Z,Z‐[10]annulene. In contrast, the radical cation (1⋅+ ⋅ SbCl6−) possesses a doubly twisted Hückel topology. Furthermore, the dication (12+ ⋅ 2SbCl6−) displays conformational flexibility in solution and crystalizes with the simultaneous presence of Möbius‐twisted (1a2+ ⋅ 2SbCl6−) and Hückel‐planar (1b2+ ⋅ 2SbCl6−) isomers in its unit cell. Detailed experimental measurements and theoretical calculations reveal that: (1) 1 demonstrates localized aromaticity with an alternating benzenoid/quinoid structure; (2) 1a2+ ⋅ 2SbCl6− and 1b2+ ⋅ 2SbCl6− with 48π electrons are weakly Möbius aromatic and Hückel antiaromatic, respectively; (3) 14+ ⋅ 4SbF6− exhibits Hückel aromaticity (46π) and open‐shell diradical character. [ABSTRACT FROM AUTHOR]