Bonding in ClFn (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 ClFn 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 ClFn (n=1-7) and low-lying excited states for ClF and ClF2 • MRCI/MRCI+Q: ClF (1S+,3P), ClF+ (4S-, 2P) • GVB Guidelines 1S + Cl F 90 Cl Guidelines 1S + A. Recoupled pair bonding (RPB) makes two electrons available for bonding. 1. 1st RPB Cl Weaker than covalent bond (CB) 3P Antibonding character long Re 2nd RPB nd 2. 2 RPB: Cl Stronger than 1st RPB 2P Often stronger than CB Res (1st + 2nd RPB) < Re(1st RPB) 2nd RPB favored over CB F Cl 3. Linear or quasilinear for two RPBs 2A with strong p character orbitals B. Bonding will rearrange to maximize the stability F 90 F 2B 1 F F Cl F 2A 1 Predictions Results RCCSD(T)/AVQZ results Bond length in Å Bond Energy in kcal/mol F 4A 2 101.4 1.969 F Cl 4.1 49.9 1.674 54.0 3P 2A 82.5 1.765 4.8 Cl 67.6 F -2.7 13.7 1.991 F 56.7 1S + Cl F 66.7 2B 1 63.0 1.704 71.4 3.7 61.5 Cl 14.7 F 1.699 F 152.8 Cl 1.708 1A 1 F3 2A 1 49.3 1.599 87.1 F F1 F2 Cl 1.699 RCCSD(T)/AVQZ results, except AVTZ for ClF7 Bond length in Å Bond Energy in kcal/mol Hypervalent Hypervalent w rearrangement Covalent w antibonding e- Covalent ClF4(2A1) ClF5(1A1) F F F F ClF6(2A1g) F ClF7(1A1) F F F F F F 10.9 1.5 F5 F5 85.6 1.683Å F4 F2 Cl F3 F1-Cl-F3=162.7 1.597Å F4 F1 F2 Cl F3 1.660Å F1 F2 1.572Å 1.676Å F4 Cl F3 F6 F1-Cl-F3=171.2 F -34.9 F1 88.7 F F 46.8 F F F F F Cl Cll F F F F5 F1 F3 F4 1.752Å Cl F2 F3 F6 Energy (kcal/mol) Results: Potential energy surfaces (PES) of ClF RClF (Angstrom) RClF (Angstrom) Potential energy curves for low-lying states of ClF calculated at MCSCF, MRCI+Q and RCCSD(T) levels with AV5Z basis sets. (a) 1Σ+ ground state; (b) 3П excited state. •ClF(3P) is not bound at the MCSCF level Results: 2D GVB orbitals of ClF (3П) •AVTZ level Results: 2D GVB orbitals of ClF (3П) in comparison with SF(4S-) GVB: 7sL Cl GVB: 7sR F Cl F NO: 8s Cl F 2.01 Å (Re) s=0.91 1.61 Å s=0.92 For ClF (3P), recoupling continues after R < Re S F S s=0.91 •AVTZ level F S F 1.90 Å (Re) Comparison: PES of SF and ClF Energy (kcal/mol) Hypervalent Te (kcal/mol) Covalent SF(2P 4S-) ClF(1S+ 3P) RClF (Angstrom) 47.1 56.7 Oscillating Bond Energies in SFn and ClFn SF5-F SF3-F SF-F Energy (kcal/mol) S-F SF2-F Cl-F 2st RPB SF -F 4 1st RPB ClF4-F ClF2-F ClF-F ClF3-F Conclusions • Trends in the calculated geometries and energies agree with predictions using recoupled pair bonding model. • Similar oscillating trends are found in both the SFn and ClFn series, and the differences are consistent with the difference between S and Cl at the atomic level. • Future work: a. PFn 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+F2 ClF3 Acknowledgment • Funded by the Distinguished Chair for Research Excellence in Chemistry at the University of Illinois at Urbana-Champaign.