Fused-Pentagon C70Cl6 and C70Cl8 Obtained via Chlorination-Promoted Skeletal Transformation of IPR C70

Deep learning-driven prediction of chemical addition patterns for carboncones and fullerenes

Carboncones and fullerenes are exemplary π-conjugated carbon nanomaterials with unsaturated, positively curved surfaces, enabling the attachment of atoms or functional groups to enhance their physicochemical properties. However, predicting and understanding the addition patterns in functionalized carboncones and fullerenes are extremely challenging due to the formidable complexity of the regioselectivity exhibited in the adducts. Existing predictive models fall short in systems where the carbon molecular framework undergoes severe distortion upon high degrees of addition. Here, we propose an incremental deep learning approach to predict regioselectivity in the hydrogenation of carboncones and chlorination of fullerenes. Utilizing exclusively graph-based features, our deep neural network (DNN) models rely solely on atomic connectivity, without requiring 3D molecular coordinates as input or their iterative optimization. This advantage inherently avoids the risk of obtaining chemically unreasonable optimized structures, enabling the handling of highly distorted adducts. The DNN models allow us to study regioselectivity in hydrogenated carboncones of C70H20 and C62H16, accommodating up to at least 40 and 30 additional H atoms, respectively. Our approach also correctly predicts experimental addition patterns in C50Cl10 and C76Cln (n = 18, 24, and 28), whereas in the latter cases all other known methods have been proven unsuccessful. Compared to our previously developed topology-based models, the DNN's superior predictive power and generalization ability make it a promising tool for investigating complex addition patterns in similar chemical systems.

Non-classical (NC), heptagon-containing fullerenes obtained via chlorination-promoted cage transformations: C76(NC2a)Cl24 and C76(NC2b)Cl28

High-temperature chlorination of C76 fullerene with SbCl5 proceeds via five Stone-Wales rearrangements, resulting in non-classical (NC) C76(NC1a)Cl24 with two heptagons and 14 pentagons partically fused in pairs and triples. C76(NC2b)Cl28 with isomeric carbon cage was obtained by chlorination-promoted cage shrinkage of C80via two C2 losses. The pathways of skeletal cage trasformations, the chlorination patterns, and formation energies are discussed in detail.

Chlorination-Promoted Skeletal Transformations in Isolated-Pentagon Rule (IPR) Isomers of Fullerene C86 to Non-IPR Chloro- and Trifluoromethyl Derivatives

Fullerene C86 contains two isomers obeying the Isolated-Pentagon Rule (IPR), CS-C86(16) and C2-C86(17). Both isomers undergo unprecedented skeletal transformations at high-temperature (400 °C) chlorination with SbCl5. One-step Stone-Wales rearrangement (SWR) in C86(17) results in the pentagon-fused #63614C86 cage found in the structure of #63614C86Cl24. CF3 derivatives with the same cage, two isomers of #63614C86(CF3)18 and #63614C86(CF3)18O2, were obtained by high-temperature trifluoromethylation of the chlorination products with CF3I, followed by HPLC separation. The skeletal transformation of C86(16) proceeds via two SWRs under the formation of a #63624C86 cage with one fused-pentagon pair found in the structure of #63624C86(CF3)18. The addition patterns in skeletally transformed molecules are discussed in detail, disclosing the influence of the pentagon fusions, isolated C=C bonds, and benzenoid rings on the stability of the molecules with non-IPR C86 cages. The chlorination-promoted SWRs in C86 isomers have been observed for the first time, which contribute a lot to the understanding of skeletal transformations in fullerenes.

Structural Chemistry of Pentagon-Fused C82 Fullerene Derivatives #39173C82(CF3)14,16,18 and #39173C82Cl28

High-temperature chlorination of the most stable Isolated-Pentagon-Rule (IPR) isomer of fullerene C₈₂, C₂-C₈₂(3), invariably produces non-IPR ^#39173C₈₂Cl₂₈, containing one pentagon-pentagon fusion in the carbon cage. High-temperature trifluoromethylation of ^#39173C₈₂Cl₂₈ followed by HPLC separation resulted in the isolation and structure elucidation of eight ^#39173C₈₂(CF₃)_n (n = 14, 16, 18) compounds. Structural chemistry of ^#39173C₈₂(CF₃)_14,16,18 and ^#39173C₈₂Cl₂₈ is characterized by the variation of the addition patterns in the region of a pentagon-pentagon fusion. The regiochemistry of CF₃ addition in the remaining cage region is similar to that of the known IPR C₈₂(3)(CF₃)_n compounds. Theoretical calculations revealed that ^#39173C₈₂(CF₃)_n possess lower thermodynamic stability than isomeric IPR derivatives.

Crippling the C70 fullerene: non-classical C68Cl26(OH)2 and C68Cl25(OH)3 with three heptagons and only fused pentagons via chlorination-promoted skeletal transformations

High-temperature (440 °C) chlorination of C₇₀ with SbCl₅ promotes Stone-Wales transformations and loss of the C₂ fragment, which results in a non-classical C₆₈Cl₂₈ partially hydrolyzed to C₆₈Cl₂₆(OH)₂ and C₆₈Cl₂₅(OH)₃. X-ray diffraction reveals an unprecedented C₆₈ cage with three heptagons and 15 pentagons arranged in fused pairs and triples. The shortest possible transformation pathways include one C₂ loss step and four Stone-Wales transformation steps.