Closed-shell Configuration Research Articles

On-Surface Synthesis of Non-Benzenoid Nanographenes Embedding Azulene and Stone-Wales Topologies.

The incorporation of non-benzenoid motifs in graphene nanostructures significantly impacts their properties, making them attractive for applications in carbon-based electronics. However, understanding how specific non-benzenoid structures influence their properties remains limited, and further investigations are needed to fully comprehend their implications. Here, we report an on-surface synthetic strategy toward fabricating non-benzenoid nanographenes containing different combinations of pentagonal and heptagonal rings. Their structure and electronic properties were investigated via scanning tunneling microscopy and spectroscopy, complemented by computational investigations. After thermal activation of the precursor P on the Au(111) surface, we detected two major nanographene products. Nanographene Aa-a embeds two azulene units formed through oxidative ring-closure of methyl substituents, while Aa-s contains one azulene unit and one Stone-Wales defect, formed by the combination of oxidative ring-closure and skeletal ring-rearrangement reactions. Aa-a exhibits an antiferromagnetic ground state with the highest magnetic exchange coupling reported up to date for a non-benzenoid containing nanographene, coexisting with side-products with closed shell configurations resulted from the combination of ring-closure and ring-rearragement reactions (Ba-a , Ba-s , Bs-a and Bs-s ). Our results provide insights into the single gold atom assisted synthesis of novel NGs containing non-benzenoid motifs and their tailored electronic/magnetic properties.

On‐Surface Synthesis of Non‐Benzenoid Nanographenes Embedding Azulene and Stone‐Wales Topologies

AbstractThe incorporation of non‐benzenoid motifs in graphene nanostructures significantly impacts their properties, making them attractive for applications in carbon‐based electronics. However, understanding how specific non‐benzenoid structures influence their properties remains limited, and further investigations are needed to fully comprehend their implications. Here, we report an on‐surface synthetic strategy toward fabricating non‐benzenoid nanographenes containing different combinations of pentagonal and heptagonal rings. Their structure and electronic properties were investigated via scanning tunneling microscopy and spectroscopy, complemented by computational investigations. After thermal activation of the precursor P on the Au(111) surface, we detected two major nanographene products. Nanographene Aa−a embeds two azulene units formed through oxidative ring‐closure of methyl substituents, while Aa−s contains one azulene unit and one Stone‐Wales defect, formed by the combination of oxidative ring‐closure and skeletal ring‐rearrangement reactions. Aa−a exhibits an antiferromagnetic ground state with the highest magnetic exchange coupling reported up to date for a non‐benzenoid containing nanographene, coexisting with side‐products with closed shell configurations resulted from the combination of ring‐closure and ring‐rearragement reactions (Ba−a, Ba−s, Bs‐a and Bs−s). Our results provide insights into the single gold atom assisted synthesis of novel NGs containing non‐benzenoid motifs and their tailored electronic/magnetic properties.

Twisted Diindeno-Fused Dibenzo[a,h]anthracene Derivatives and their Dianions.

We report a facile synthesis of diindeno-fused dibenzo[a,h]anthracene derivatives (DIDBA-2Cl, DIDBA-2Ph, and DIDBA-2H) with different degrees of non-planarity using three substituents (chloro, phenyl, and hydrogen) of varying sizes. The planarization of their cores, as evidenced by the decreased end-to-end torsional angles, was confirmed by X-ray crystallography. Their enhanced energy gaps with twisting were investigated by a combination of spectroscopic and electrochemical methods with density functional theory, resulting in a transition from singlet open-shell to closed-shell configuration. Moreover, their doubly-reduced states, DIDBA-2Ph2- and DIDBA-2H2-, were achieved by chemical reduction. The structures of dianions were identified by X-ray crystallographic analysis, elucidating that the electron charging further distorted the backbones. The electronic structure of the dianions was demonstrated by experimental and theoretical approaches, suggesting decreased energy gaps with larger non-planarity, different from the neutral species.

Octupole deformation of nuclei near the spherical closed-shell configurations

Octupole deformation of nuclei near the spherical closed-shell configurations

Introducing Novel Materials with Diffuse Electrons for Applications in Redox Catalysis and Quantum Computing via Theoretical Calculations

Diamond-like structures, where carbon atoms have been replaced with Li+ and C–C bonds with diamines, have currently been introduced as new materials, which can host diffuse electrons in the periphery of each lithium tetra-amine center. These materials display a diverse range of properties behaving as metals or semiconductors depending on the diamine chain length. Multi-reference wavefunction and density functional theory calculations were employed to study the electronic structure of these materials. Initially, gas phase calculations are performed on isolated (NH3)3LiNH2(CH2)1–10H2NLi(NH3)3 molecular strings. One diffuse electron surrounds the periphery of each −NH2Li(NH3)3 terminus. The two terminal electrons couple into a triplet and open-shell singlet states, which are nearly degenerate for long chains and as closed shell singlets for short. At intermediate lengths, the wavefunction of the ground-state singlet state mixes both open- and closed-shell configurations raising doubts about which configuration should be considered for density functional theory calculations. Observations from gas phase calculations accurately predict properties from the condense phase density functional theory calculations carried out for proposed crystalline Li-diamine materials, offering an avenue for further development and insight. Spin-polarized and unpolarized calculations are performed for the whole range of hydrocarbon sizes reporting geometrical and electronic band structures, spin density contours, and density of states. Diffuse electrons can be used for redox reactions or can serve as qubits for quantum computing. Future work will focus on decorating the hydrocarbon backbone with functional groups and/or bulky units, in order to facilitate or block the association between neighboring electrons for more controlled quantum computing applications and propose materials for selective redox catalysis.

Probing the structural evolution, electronic and vibrational properties of anionic sodium-doped magnesium clusters

Bimetallic clusters aroused a great deal of attention in materials science because of their novel properties, depending sensitively on their size, structure, and composition. Herein, we report a theoretical study of the geometry, stability, electronic and vibrational properties of bimetallic NaMgn– (n = 2–11) clusters through CALYPSO code within DFT calculations. The most stable NaMgn– clusters were found to be planar structure at n = 2, triangular pyramid-based structure at n = 3–5, pentagonal pyramid-based structure at n = 6–7 and the triangular prism-based structure at n = 8–11. Most of them are structurally consistent with anionic magnesium clusters, in which the Na atom tends to localize on the convex site. Stability studies conform to the NaMg3– and NaMg9–clusters to being the magic number structure with prominent stability, which benefits from short interatomic bonds and closed-shell 1S21P6 and 1S21P61D102S2 electronic configurations. Bonding nature analysis not only reflects the delocalized bonding properties in the NaMg3– and NaMg9– clusters, but also reveals that the Mg-Mg bond is stronger than the Na-Mg bond. For the NaMgn– clusters, calculated PES, IR, and Raman spectra could be used as essential evidence for identifying cluster structures experimentally in the future.

Axial and triaxial degrees of freedom in 72Zn

The unstable N=42 nucleus 72Zn has been studied using multiple safe Coulomb excitation in inverse kinematics. The experiment was performed at the REX-ISOLDE facility at CERN making first use of the silicon detector array C-REX in combination with the γ-ray spectrometer Miniball. The high angular coverage of C-REX allowed to determine the reduced transition strengths for the decay of the yrast 01+, 21+ and 41+ as well as of the 02+ and 22+ states in 72Zn. The quadrupole moments of the 21+, 41+ and 22+ states were extracted. Using model independent quadrupole invariants, the ground state of 72Zn was found to have an average deformation in the γ degree of freedom close to maximum triaxiality. In comparison to experimental data in zinc isotopes with N<40, the collectivity of the 41+ state in neutron-rich 72Zn is significantly larger, indicating a collective yrast band based on the ground state of 72Zn. In contrast, a low experimental B(E2;02+→21+) strength was determined, indicating a different structure for the 02+ state. Shell-model calculations propose a 02+ state featuring a larger fraction of the (spherical) N=40 closed-shell configuration in its wave function than for the 01+ ground state.The results were also compared with beyond mean field calculations which corroborate the large deformation in the γ degree of freedom, while pointing to a more deformed 02+ state. These experimental and theoretical findings establish the importance of the γ degree of freedom in the ground state of 72Zn, located between the 68,70Ni nuclei that have spherical ground states, and 76Ge, which has a rigid triaxial shape.

Probing the effects of lithium doping on structures, properties, and stabilities of magnesium cluster anions

Bimetallic clusters have aroused tremendous interest because the property changes like structure, size, and composition have occurred. Herein, a structural search of the global minimum for anionic (n = 2–11) clusters is performed using an efficient crystal structure analysis by particle swarm optimization (CALYPSO) structural searching program with subsequent density functional theory (DFT) calculations. A great variety of low energetic isomers are converged, and the most stable ones are confirmed by comparing their total energy of each size. It is found that the clusters are structurally consistent with corresponding Mg clusters anions except for and . In all the doped clusters, the Li atom prefers to occupy the convex position. Simulated photoelectron spectra (PES), Infrared (IR), and Raman spectra of could be used as an essential evidence for identifying cluster structures experimentally in the future. Stability study reveals that a tower-like structure of has prominent stability and can be identified as a magic number cluster. The reason might be that there are both closed-shell 1S21P61D102S2 electronic configurations and stronger Li–Mg bonds caused by sp hybridization in the cluster.

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl3 (RE = Sc, Y, Lanthanides) Series.

Atomic packing and electronic structure are key factors underlying the crystal structures adopted by solid-state compounds. In cases where these factors conflict, structural complexity often arises. Such is born in the series of REAl3 (RE = Sc, Y, lanthanides), which adopt structures with varied stacking patterns of face-centered cubic close packed (FCC, AuCu3 type) and hexagonal close packed (HCP, Ni3Sn type) layers. The percentage of the hexagonal stacking in the structures is correlated with the size of the rare earth atom, but the mechanism by which changes in atomic size drive these large-scale shifts is unclear. In this Article, we reveal this mechanism through DFT-Chemical Pressure (CP) and reversed approximation Molecular Orbital (raMO) analyses. CP analysis illustrates that the Ni3Sn structure type is preferable from the viewpoint of atomic packing as it offers relief to packing issues in the AuCu3 type by consolidating Al octahedra into columns, which shortens Al-Al contacts while simultaneously expanding the RE atom's coordination environment. On the other hand, the AuCu3 type offers more electronic stability with an 18-n closed-shell configuration that is not available in the Ni3Sn type (due to electron transfer from the RE dz2 atomic orbitals into Al-based states). Based on these results, we then turn to a schematic analysis of how the energetic contributions from atomic packing and the electronic structure vary as a function of the ratio of FCC and HCP stacking configurations within the structure and the RE atomic radius. The minima on the atomic packing and electronic surfaces are non-overlapping, creating frustration. However, when their contributions are added, new minima can emerge from their combination for specific RE radii representing intergrowth structures in the REAl3 series. Based on this picture, we propose the concept of emergent transitions, within the framework of the Frustrated and Allowed Structural Transitions principle, for tracing the connection between competing energetic factors and complexity in intermetallic structures.

Electrical conductivity through π-π stacking in a two-dimensional porous gallium catecholate metal-organic framework.

Metal-organic frameworks (MOFs) are hybrid materials known for their nanoscale pores, which give them high surface areas but generally lead to poor electrical conductivity. Recently, MOFs with high electrical conductivity were established as promising materials for a variety of applications in energy storage and catalysis. Many recent reports investigating the fundamentals of charge transport in these materials focus on the role of the organic ligands. Less consideration, however, is given to the metal ion forming the MOF, which is almost exclusively a late first-row transition metal. Here, we report a moderately conductive porous MOF based on trivalent gallium and 2,3,6,7,10,11-hexahydroxytriphenylene. Gallium, a metal that has not been featured in electrically conductive MOFs so far, has a closed-shell electronic configuration and is present in its trivalent state-in contrast to most conductive MOFs, which are formed by open-shell, divalent transition metals. Our material, made without using any harmful solvents, displays conductivities on the level of 3 mS/cm and a surface area of 196 m2 /g, comparable to transition metal analogs.

Dioxygen Activation by Redox-Active Bis(aldimine) Ligand Bridged Diruthenium Complex Possessing Singlet Ground State.

The unexplored 'actor' behavior of redox-active bis(aldimine) congener, p-phenylene-bis(picoline)aldimine (L1), towards dioxygen activation and subsequent functionalization of its backbone was demonstrated on coordination with {Ru(acac)2 } (acac= acetylacetonate). Reaction under aerobic condition led to the one-pot generation of dinuclear complexes with unperturbed L1, imino-carboxamido (L2- ), and bis(carboxamido) (L32- )-bridged isovalent {RuII (μ-L1)RuII }, 1/ {RuIII (μ-L32- )RuIII }, 3 and mixed-valent {RuII (μ-L2- )RuIII }, 2. Authentication of the complexes along with the redox non-innocence behavior of their bridge have been validated through structure, spectroelectrochemistry and DFT calculations. Kinetic and isotope labelling experiments together with DFT analyzed transition states justified the consideration of redox shuttling at metal/L1 interface for 3 O2 activation despite of the closed shell configuration of 1 (S=0) to give carboxamido derived 2/3.

From the gas phase to the solid state: The chemical bonding in the superheavy element flerovium.

As early as 1975, Pitzer suggested that copernicium, flerovium, and oganesson are volatile substances behaving like noble gas because of their closed-shell configurations and accompanying relativistic effects. It is, however, precarious to predict the chemical bonding and physical behavior of a solid by knowledge of its atomic or molecular properties only. Copernicium and oganesson have been analyzed very recently by our group. Both are predicted to be semiconductors and volatile substances with rather low melting and boiling points, which may justify a comparison with the noble gas elements. Here, we study closed-shell flerovium in detail to predict its solid-state properties, including the melting point, by decomposing the total energy into many-body forces derived from relativistic coupled-cluster theory and from density functional theory. The convergence of such a decomposition for flerovium is critically analyzed, and the problem of using density functional theory is highlighted. We predict that flerovium in many ways does not behave like a typical noble gas element despite its closed-shell 7p1/2 2 configuration and resulting weak interactions. Unlike the case of noble gases, the many-body expansion in terms of the interaction energy does not converge smoothly. This makes the accurate prediction of phase transitions very difficult. Nevertheless, a first prediction by Monte Carlo simulation estimates the melting point at 284 ± 50 K. Furthermore, calculations for the electronic bandgap suggests that flerovium is a semiconductor similar to copernicium.

B8C10: A C2v planar polycyclic structure bridged by the central strong C[sbnd]C bond and strengthened by the aromaticity

Global-searching for B8C10− anion and B8C10 neutral is executed based on CALYPSO genetic algorithm with DFT calculations, and their structural and bonding properties are investigated by quantum chemical calculations. B8C10− anion has a cross-bridged three-ringed structure, while B8C10 neutral adopts a C2v symmetric planar polycyclic structure cross-bridged by the central CC bond. B8C10− can be regarded as a superhalogen anion because of the large VDE of 3.56 eV. B8C10 neutral has a closed-shell electronic configuration with HOMO-LUMO gap of 2.44 eV and σ plus π double delocalized bonding characters. More interestingly, B8C10 neutral exhibits some aromaticity.

A 2D perchlorinated sp2-carbon framework

Two-dimensional (2D) π-conjugated polymers are promising electronic materials with diverse properties controlled by varying the structure of organic building blocks. We here report an organic framework with perchlorotriphenylmethyl (PTM) radical nodes, synthesized through dehalogenative thermolysis polymerization of tris(iodotetrachlorophenyl)methane. The resulting C-C-linked P2PTM is characterized by X-ray photoelectron, NMR, Raman, and FTIR spectroscopies and X-ray diffraction. Exfoliated, layered 2D sheets can be imaged with TEM and AFM. N2 adsorption experiment indicates a permanent porosity with a surface area of 150 m2/g, and dynamic vapor sorption shows a specific adsorption of one chloroform molecule per P2PTM unit cell, in line with modeling. DFT calculations predict degenerate Mott-insulating antiferromagnetic and ferromagnetic states, while the semi-metallic closed-shell configuration is less stable by ∼1 eV. Experimentally, P2PTM is a low-bandgap black solid with moderate electrical conductivity (∼4 × 10−4 S cm−1), gate-modulated ambipolar charge transport and paramagnetic behavior down to 1.9 K.

Hydrogen-Bonded Complexes of Neutral Nitroxide Radicals with 2-Propanol Studied by Multifrequency EPR/ENDOR

The hydrogen bond plays a key role in weak directional intermolecular interactions. It is operative in determining molecular conformation and aggregation, and controls the function of many chemical systems, ranging from inorganic, organic to biological molecules. Although an enormous amount of spectroscopic information has been collected about hydrogen-bond formation between molecules with closed-shell electronic configuration, the details of such interactions between open-shell radicals and closed-shell molecules are still rare. Here we report on an investigation of hydrogen-bonded complexes between pyrroline-type as well as piperidine-type neutral nitroxide radicals and an alcohol, i.e., 2-propanol. These nitroxide radicals are commonly used as EPR spin labels and probes. To obtain information on the geometry of the complexes and their electronic structure, multi-resonance EPR techniques at various microwave frequencies (X-, Q-, W-band, 244 GHz) have been employed in conjunction with DFT calculations. The planar five-membered ring system of the pyrroline-type nitroxide radical was found to form exclusively well-defined in-plane σ-type hydrogen-bonded complexes with one 2-propanol molecule in the first solvation shell in frozen solution. The measured hyperfine parameters of the hydrogen-bridge proton and the internal magnetic parameters describing the electron Zeeman and the electron-nuclear hyperfine and nuclear quadrupole interactions are in good agreement with values predicted by state-of-the-art DFT calculations. In contrast, multi-resonance EPR on the non-planar six-membered ring system of the piperidine-type nitroxide radical (TEMPOL) reveals a more complex situation, i.e., a mixture of a σ-type with, presumably, an out-of-plane π-type complex, both present in comparable fraction in frozen solution. For TEMPOL, the DFT calculations failed to predict magnetic interaction parameters that are in good agreement with experiment, apparently due to the considerable flexibility of the nitroxide and hydrogen-bonded complex. The detailed information about nitroxide/solvent complexes is of particular importance for Dynamic Nuclear Polarization (DNP) and site-directed spin-labeling EPR studies that employ nitroxides as polarizing agents or spin labels, respectively.

Three-State Switching of an Anthracene Extended Bis-thiaxanthylidene with a Highly Stable Diradical State.

A multistable molecular switching system based on an anthracene-extended bis-thiaxanthylidene with three individually addressable states that can be interconverted by electrochemical, thermal, and photochemical reactions is reported. Besides reversible switching between an open-shell diradical- and a closed-shell electronic configuration, our findings include a third dicationic state and control by multiple actuators. This dicationic state with an orthogonal conformation can be switched electrochemically with the neutral open-shell triplet state with orthogonal conformation, which was characterized by EPR. The remarkably stable diradical shows kinetic stability as a result of a significant activation barrier for isomerization to a more stable neutral closed-shell folded geometry. We ascribe this activation barrier of ΔG⧧(293 K) = 25.7 kcal mol–1 to steric hindrance in the fjord region of the overcrowded alkene structure. The folded closed-shell state can be converted back to the diradical state by irradiation with 385 nm. The folded state can also be oxidized to the dicationic state. These types of molecules with multiple switchable states and in particular stable diradicals show great potential in the design of new functional materials such as memory devices, logic gates, and OFETs.

Lifetime measurements in the even-even Cd102–108 isotopes

The heaviest N=Z doubly-magic nucleus, $^{100}$Sn, and the neighboring nuclei offer unique opportunities to investigate the properties of nuclear interaction in extreme conditions. In particular, the Cd isotopes are expected to present features similar to those found in the Sn isotopic chain, since they have only two proton holes in the Z=50 shell. In this manuscript, the lifetime measurements of low-lying states in the even-mass $^{102-108}$Cd is presented. Thanks to the powerful detection capabilities of AGATA array and VAMOS++ spectrometer, the unusual employment of multi-nucleon transfer reactions permitted to investigate the first 2$^+$ and 4$^+$ states in all these nuclei, together with various deformed bands in $^{106}$Cd. The results were interpreted in the context of new state-of-the-art beyond-mean-field calculations, using the symmetry-conserving configuration-mixing approach. Despite the similarities in the electromagnetic properties of the low-lying states, there is a fundamental structural difference between the ground-state bands in the Z=48 and Z=50 isotopes. The comparison between experimental and theoretical results revealed a rotational character of the Cd nuclei, which have prolate-deformed ground states with $\beta_2 \approx 0.2$. At this deformation Z=48 becomes a closed-shell configuration, which is favored with respect to the spherical one.

Redox Ladder of Ni3 Complexes with Closed-Shell, Mono-, and Diradical Triphenylene Units: Molecular Models for Conductive 2D MOFs.

We report the isolation and characterization of a series of trinickel complexes with 2,3,6,7,10,11-hexaoxytriphenylene (HOTP), [(Me3 TPANi)3 (HOTP)](BF4 )n (Me3 TPA=N,N,N-tris[(6-methyl-2-pyridyl)methyl]amine) (n=2, 3, 4 for complexes 1, 2, 3). These complexes comprise a redox ladder whereby the HOTP core displays increasingly quinoidal character as its formal oxidation state changes from -4, to -3, and -2 in 1, 2, and 3, respectively. No formal oxidation state changes occur on Ni, allowing the isolation of singlet diradical, monoradical, and closed-shell configurations for HOTP in 1, 2, and 3, respectively, with a concomitant decrease in the spin coupling strength upon oxidation. Because the three complexes can be considered models of the smallest building blocks of 2D conductive metal-organic frameworks such as Ni9 HOTP4 , these results serve as possible inspiration for the construction of extended materials with targeted electric and magnetic properties.

Evolution of the structural and electronic properties, and dynamical fluxionality of B2Ge n −/0 (n = 3–12) clusters: emergence of B2 unit endohedral pentagonal structure and aromaticity at n = 10

ABSTRACT The evolution of structural and electronic properties, and dynamical fluxionality of B2Ge n −/0 (n = 3–12) clusters are investigated using DFT calculations combined with CALYPSO global searching algorithm. The B atoms in B2Ge n −/0 incline to bond with each other and more Ge atoms. The theoretical calculations show that B2Ge3 −/0 have planar 2D structures, while the geometries of B2Ge4-7 −/0 are all exohedral 3D structures dominated by bipyramid-shaped or bowl-shaped based configurations and those of B2Ge8-12 −/0 majorly hold prism-shaped based geometries. B2Ge10 − and B2Ge10 are confirmed as the threshold sizes of transiting from B2-exohedral to B2-endohedral geometries for anions and neutrals, respectively. Natural population analysis indicates that the electron transfers from Ge n skeletons to B atoms. Interestingly, the low-lying isomers of B2Ge4 −, B2Ge6 −, B2Ge7 −/0, B2Ge8 −/0, B2Ge9 −, and B2Ge12 − clusters exhibit dynamical fluxionality. The ΔE I, Δ2 E, and ΔE I values versus number of Ge atoms suggest that B2Ge n − anions are more stable than B2Ge n neutrals, except that B2Ge10 has higher stability than B2Ge10 −. Molecular orbitals analysis of B2Ge10 indicates that it has σ + π double delocalised bonding patterns and electronic closed-shell configuration with a HOMO–LUMO gap of 2.17 eV. The nucleus-independent chemical shift (NICS) calculations indicate that B2Ge10 −/0 clusters have aromaticity.

Mechanistic Insights into the P450 TleB-Catalyzed Unusual Intramolecular C-N Bond Formation Involved in the Biosynthesis of Indolactam V.

Indolactam V, a known biosynthetic precursor of indolactam alkaloids, is the main pharmacophore of this family and exhibits potential protein kinase C activation. A key step in the biosynthesis of indolactam V is the formation of an indole-fused nine-membered lactam core by intramolecular C-N bond formation. In this work, we report a computational study of the unique cytochrome P450 TleB enzyme-catalyzed direct and selective C-H bond amination reaction that can generate indolactam V from the dipeptide N-methylvalyl-tryptophanol. By performing molecular dynamics simulations and quantum-mechanical/molecular-mechanical calculations, we revealed that the C-H bond amination involves one step of proton transfer from N1-H of the indole ring to the FeIV═O unit, one step of hydrogen abstraction of N13-H in the side chain of the substrate by the FeIV-OH unit, and diradical coupling, in which two conformational changes of the side chain of the substrate are necessary. In the enzyme-substrate complex of TleB, the N-H bond of the indole ring of the substrate forms a strong hydrogen bond with the FeIV═O unit in compound I, and the porphyrin radical cation accepts an electron from the substrate to form the closed-shell electronic configuration. Thus, compound I in the enzyme-substrate complex cannot be described as FeIV═O coupled to a porphyrin radical cation, which is different from those of other P450 enzymes. Besides, two stages of conformational changes of the side chains of the substrate may increase the relative energies of reaction intermediates by 10-12 kcal/mol. From the structure point of view, it is the rotatable long side chain of the substrate and the large flexible active pocket of TleB that make the intramolecular diradical coupling feasible. Our findings may provide useful information to further understand the Tleb-catalyzed intramolecular C-H bond amination and the other bio-catalyzed intramolecular diradical coupling.