Characterization of Novel Polyhalogen Monoanions

• Applicants: Professor Dr. Sebastian Hasenstab-Riedel; Professorin Dr. Beate Paulus
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320971935

• Final Report Year: 2022

Final Report Abstract

Poly- and interhalogen species offer a variety of interesting properties to investigate. On the fundamental level, a thorough comprehension of the non-covalent halogen bonding that facilitates the formation of aggregates of di- and interhalogen molecules and halide anions is important. It is key to understanding the formation, structure, and properties of the poly- and interhalogen species and identifying potential applications. One important step for this is broadening the scope of available polyhalogen and likewise interhalogen anions through preparation and appropriate characterization in experiment. Another one is the detailed studying of the halogen bonding and its interplay with environmental forces through quantum chemical modeling. In the course of this project, both steps were taken. Using a combination of laser ablation, matrix isolation, and vibrational spectroscopy, cation-independent Cl3− anions were prepared and characterized for the first time. The same methodological protocol was successfully employed in studies of other novel molecular systems as well. Likewise, a crystal structure containing highly symmetric trichloride anions was reported. This is unusual given that previously observed corresponding crystal structures featured only asymmetric Cl3− anions. For these experimental studies, quantum chemical modeling in the form of density functional theory as well as wavefunctionbased methods was used to complement the experimental findings and offer explanations for the observations. Beyond that ab initio methods were employed in more detailed theoretical studies of extended guest-matrix systems. For this, a computational workflow was set up to determine a potential energy surface for arbitrarily large molecule-noble gas structures on the basis of explicitly correlated coupled cluster calculations, to find favorable guest-host environments and to calculate highly accurate vibrational excitation energies of the molecule in the presence of the host. The resulting scheme was applied to trifluoride anions trapped in neon and argon matrices, respectively, and allowed for an accurate reproduction of the experimental observations. Moreover, the modeling sheds light on the nature of the guest-host interactions in the different noble gas matrices and their effect on an trapped species. With respect to this, a striking observation is the importance of three-body F3− -Ar2 interactions for an accurate description of the molecular vibrations. Likewise, the modeling provided information on the structural properties of the host environment, which as of now, is not directly available from experiment. Accordingly, the trifluoride is most likely isolated in a double-vacancy site in either noble gas fcc structure. Another insight gained from the modeling concerns the formation of the matrix sites. The analysis of molecular dynamics simulations on F3− in argon indicated that the formation of the favored double-vacancy environment over a similarly stable single-vacancy site might be caused by kinetic effects.

Publications

• “Matrix-isolation and comparative far-IR investigation of free linear [Cl3 ]− and a series of alkali trichlorides” Chem. Commun. 53, 12958 (2017)
  F. Redeker, H. Beckers, S. Riedel
  
• “Theoretical investigation of the structures, stabilities and vibrational properties of triatomic interhalide ions and their alkali ion pairs” J. Fluorine Chem. 216, 81 (2018)
  F. Redeker, A. Kropman, C. Müller, S. Zewge, H. Beckers, B. Paulus, S. Riedel
  
• “A validation of cluster modeling in the description of matrix isolation spectroscopy” J. Comput. Chem. 41, 751 (2020)
  F. Bader, T. Lindic, B. Paulus
  
• “Matrix Isolation of Ions and Ion Pairs” Dissertation, 2020
  F. Redeker
  
• “A pair potential modeling study of F3− in neon matrices” Phys. Chem. Chem. Phys. 23, 886 (2021)
  F. Bader, J. C. Tremblay, B. Paulus
  
• “Insights into the Topology and the Formation of a Genuine ppσ Bond: Experimental and Computed Electron Densities in Monoanionic Trichlorine [Cl3 ]− ” Angew. Chem. Int. Ed. 60, 2569 (2021)
  H. Keil, K. Sonnenberg, C. Müller, R. Herbst-Irmer, H. Beckers, S. Riedel, D. Stalke
  
• “Matrix Isolation Spectroscopy of Small Molecules: An ab initio Modeling Study” Dissertation, 2021
  F. Bader
  
• “The peculiar interaction of Trifluoride Anions with Cryogenic Rare Gas Matrices” J. Phys. Chem. A 125, 6221 (2021)
  F. Bader, S. Riedel, H. Beckers, C. Müller, J. C. Tremblay, B. Paulus
  
• “Theoretical modeling of molecules in weakly interacting environments: Trifluoride anions in argon” Phys. Chem. Chem. Phys. 24, 3555 (2022)
  F. Bader, J. C. Tremblay, B. Paulus