Bonding in ClF n (n=1-7): Further Insights into Hypervalent Molecules and Recoupled Pair Bonds Lina Chen, David E. Woon and Thom H. Dunning Department of Chemistry University of Illinois at Urbana-Champaign Columbus, Ohio June 25, 2009

Motivation Test the robustness of the recoupled pair bonding (RPB) model Obtain the optimized structures and energies of low-lying states of ClF n and ClF + species Explore the dependence of bond energies on the choice of the hypervalent atom, comparing S and Cl. Identify factors that influence the bonding efficiency.

Methodology RCCSD(T) : ground states of ClF n (n=1-7) and low-lying excited states for ClF and ClF 2 MRCI/MRCI+Q: ClF ( 1  ,   ), ClF + ( 4  ,    ) GVB

Guidelines 90  Cl F 1+1+

Guidelines A.Recoupled pair bonding (RPB) makes two electrons available for bonding st RPB Weaker than covalent bond (CB) Antibonding character  long R e 2. 2 nd RPB: Stronger than 1 st RPB Often stronger than CB R e s (1 st + 2 nd RPB) < R e (1 st RPB) 2 nd RPB favored over CB 3. Linear or quasilinear for two RPBs with strong p character orbitals B. Bonding will rearrange to maximize the stability 90  Cl F 1+1+ 33 22 F 2A2A FF F F 2 nd RPB 2B12B1 2A12A1

Predictions

Results F3 F1 F  Cl F Cl F Cl RCCSD(T)/AVQZ results Bond length in Å Bond Energy in kcal/mol  82.5   66.7 FFCl FF FF +1+ 33 2A12A1 2B12B1 2A 4A24A2 1A11A1

F F F F ClF 4 ( 2 A 1 )ClF 7 ( 1 A 1 ) FF F F F ClF 5 ( 1 A 1 )ClF 6 ( 2 A 1g ) F F F F F F Cll Cl F F F F F F F F3 F1 F2F Å 88.7   F1-Cl-F3=162.7  ClF3 F1 F2 F Å 85.6  F5 Cl 1.660Å  F1-Cl-F3=171.2  F3 F1 F2 F Å F5 Cl F6 F3 F1 F2 F4 F5 Cl F6 F Å 1.752Å RCCSD(T)/AVQZ results, except AVTZ for ClF 7 Bond length in Å Bond Energy in kcal/mol Covalent HypervalentHypervalent w rearrangement Covalent w antibonding e -

Results: Potential energy surfaces (PES) of ClF Potential energy curves for low-lying states of ClF calculated at MCSCF, MRCI+Q and RCCSD(T) levels with AV5Z basis sets. (a) 1 Σ + ground state; (b) 3 П excited state. ClF( 3  ) is not bound at the MCSCF level R ClF (Angstrom) Energy (kcal/mol) R ClF (Angstrom)

Results: 2D GVB orbitals of ClF ( 3 П) AVTZ level

Results: 2D GVB orbitals of ClF ( 3 П) in comparison with SF( 4  - ) SFSFSF NO: 8  GVB: 7  L GVB: 7  R 2.01 Å (R e ) 1.61 Å 1.90 Å (R e ) s=0.91 s=0.92 s=0.91 AVTZ level For ClF ( 3  ), recoupling continues after R < R e ClF F F

Comparison: PES of SF and ClF R ClF (Angstrom) Energy (kcal/mol) Hypervalent Covalent T e (kcal/mol) SF( 2   4  - ) 47.1 ClF( 1  +  3  ) 56.7

Oscillating Bond Energies in SF n and ClF n Cl-F ClF-F ClF 2 -F ClF 3 -F ClF 4 -F S-F SF-F SF 2 -F SF 3 -F SF 4 -F SF 5 -F Energy (kcal/mol) 1 st RPB 2 st RPB

Conclusions Trends in the calculated geometries and energies agree with predictions using recoupled pair bonding model. Similar oscillating trends are found in both the SF n and ClF n series, and the differences are consistent with the difference between S and Cl at the atomic level. Future work: a. PF n series as well as various combinations of P, S, Cl and F with other ligands such as monovalent H, Cl, and OH and divalent O. b. Reactions: ClF+F 2  ClF 3

Acknowledgment Funded by the Distinguished Chair for Research Excellence in Chemistry at the University of Illinois at Urbana-Champaign.