4.7 Article

Impact of Electron-Withdrawing Effect on Sigma Hole Via Bromine-Based Interactions in Zn-5,10,15,20-tetra(4-bromo-2,6-difluoro Phenyl) Porphyrin

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CRYSTAL GROWTH & DESIGN
卷 23, 期 8, 页码 5975-5985

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AMER CHEMICAL SOC
DOI: 10.1021/acs.cgd.3c00543

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This study developed novel supramolecular structures based on a custom-designed porphyrin linker Zn(II)-5,10,15,20-tetra(4-bromo-2,6-difluorophenyl) porphyrin (Zn-BFP). The inclusion of electron-withdrawing fluorine atoms near bromine atoms increased the polarizability of the bromine atoms and their participation in halogen bonding. Three new supramolecular solids were synthesized using Zn-BFP with axial linkers nicotinic acid and 5-bromonicotinic acid, exhibiting diverse halogen bonding and hydrogen bonding motifs. The influence of fluorine atoms on the porphyrin skeleton and their participation in halogen bonding were illustrated.
This study presents the development of novel supramolecularstructuresbased on custom-designed porphyrin linker Zn(II)-5,10,15,20-tetra(4-bromo-2,6-difluorophenyl) porphyrin (Zn-BFP). The porphyrin skeleton was specificallydesigned to introduce electron-withdrawing fluorine atoms near bromineatoms. The inclusion of fluorine atoms at 2,6-positions increasesthe polarizability of bromine atoms to participate more actively inhalogen bonding interactions. The porphyrin Zn-BFP was synthesizedby Adler's method and fully characterized by (HNMR)-H-1. The absorbance, emission, and electrochemical studies of Zn-BFPwere conducted to reveal the influence of fluorine substituents onthe optical and electrochemical properties. Three new supramolecularsolids [Zn(BFP)(H2O)]& BULL;acetone (1), [Zn(BFP)(NA)]& BULL;2DCM(2), and [Zn(BFP)(5-Br-NA)(2)] (3) in crystalline forms were synthesized by employing Zn-BFPwith axial linkers nicotinic acid and 5-bromonicotinic acid. The axiallinkers provided additional interaction sites in the form of COOHgroups to involve in hydrogen bonding. Detailed single-crystal X-raydiffraction analyses revealed the existence of diverse halogen bondingcontacts Br & BULL;& BULL;& BULL;Br, Br & BULL;& BULL;& BULL;O, and Br & BULL;& BULL;& BULL;& pi;and hydrogen bonding motifs O-H & BULL;& BULL;& BULL;O betweenthe metalloporphyrin units leading to 1D chains and 2D supramolecularsheets. The findings of particular interest are the existence of relativelyshortest Br & BULL;& BULL;& BULL;Br interactions in compound 2. Hirshfeld surface analyses revealed the contributions of variousinteractions toward the stability of the extended architectures. Morphologicalstudies supported distinct supramolecular features exhibited by thefluorine-appended porphyrins. Electrostatic potential isosurfaceswith the aid of density functional theory indicated that fluorineatom substitution at the 2,6-positions of the bromo phenyl moietyenhances the & sigma;-hole potential by 5.2 kcal/mol, clearly suggestingthe expansion of the & sigma;-hole. Theinfluence of electron-withdrawing fluorine atoms onthe porphyrin skeleton enhancing the polarizability of bromine atoms,leading to significant expansion of & sigma;-hole and increasing theirparticipation in halogen bonding was illustrated with three differentsupramolecular solids.

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