Theoretical Predictions of the Structures and Energetics of ClF n +/- (n =1-6) Ions: Extended Studies of Hypervalent Species Using the Recoupled Pair Bonding Model Lina Chen, David E. Woon, Thom. H. Dunning, Jr. Department of Chemistry University of Illinois, Urbana-Champaign Columbus, Ohio June

Background  Small d-orbital contribution to the bondings in SF 3 to SF 6 1, 2  d-hybridization model un-suitable  Mostly 3s and 3p orbitals for bonding  Oscillating trend of the bond energies of SF n-1 +F  SF n was observed experimentally 3 1.Reed & Weinhold, JACS, 108,3586,1986; 2.Cooper et al, JACS, 116, 4414,1994; 3. Kiang & Zare, JACS, 102,4024,1980 StructuresEnergetics Ground States Excited States New Model: Prediction

New Model: Recoupled Pair Bond (RPB) A. RPB involves decoupling a lone pair of electrons on the central atom recoupling them with singly occupied ligand orbitals +F 1 st RPB2 nd RPB weak long R e strong short R e X( 3 P) XF( 4  - ) XF 2 ( 3 B 1 ) Excited States X=S, Cl +

New Model: Recoupled Pair Bond (RPB) B. Bonding will rearrange to maximize the stability. Rearrange XF 3 ( 2 A ’ ) RPB two RPBs one covalent bond. one RPB two covalent bond s X=S, Cl +

Applications of the Recoupled Pair Bonding 1. Oscillating Bond Energies in SF n and ClF n 1.Woon & Dunning, JPCA, 113, 7915, 2009; 2. Chen, Woon & Dunning, JPCA, 113, 12645, 2009 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 /eV RCCSD(T)/AVTZ without Zero Point Energy Correction SF n, n 2. The formation of molecules with normal valence (e.g. CX 2, X=H,F, n=1,2; TI13) Decouple the 1 st 3p 2 Decouple the 2 nd 3p 2 Decouple the 3s 2

Objectives  Predict unknown states of ClF n +/-.  Compute ionization energies and electron affinities for experimental detection.  Cl + and S are isoelectronic, as are Cl - and Ar. Identify factors that influence the strength of the RPB.

Methodology  High level ab initio methods which account for dynamical correlations.  Coupled Cluster Methods: CCSD(T) and RCCSD(T)  Molpro  Augmented correlation consistent basis sets: F: aug-cc-pVXZ Cl: aug-cc-pV(X+d)Z  Generalized Valence Bond (GVB) Diagrams X=T, Q

XF n (X=S, Cl + ): Prediction I (n=1-3) XF ( 2  ) XF( 4    XF 2 ( 1 A 1 ) XF 2 ( 3 B 1 ) XF 3 ( 2 A ’ ) covalent w/antibonding e - hypervalent w/rearrangement XF 2 ( 3 A 2 )

SF n : Results I (n=1-3) SF 3 ( 2 A’)SF 2 ( 1 A 1 ) SF 2 ( 3 B 1 ) SF 2 ( 3 A 2 ) SF( 4  – ) SF( 2  ) covalent w/antibonding e - hypervalent w/rearrangement 1.72 S S SS S S RCCSD(T)/AVTZ results without ZPE correction Bond energies in eV

ClF n + : Results I (n=1-3) F F F Cl F F FF Cl FF 2 1A11A1 3B13B1 2A’2A’ RCCSD(T)/AVTZ results without ZPE correction Bond energies in eV 44 covalent w/antibonding e - hypervalent w/rearrangement 3A23A2 Not Stable

XF n (X=S, Cl + ), (n=4-6) covalent w/antibonding e - hypervalent w/rearrangement XF 4 ( 1 A 1 )XF 5 ( 2 A 1 ) XF 6 ( 1 A 1g ) XF 3 ( 2 A 1 ) SF 3 ( 2 A’) ClF 3 + ( 2 A 1 ) Cl RCCSD(T)/AVTZ results without ZPE correction; Bond energies in eV SS S

Mulliken Populations of ClF n + and SF n StateSpeciesQ(X)Q(F equatorial )Q(F axial ) 22 SF ClF -4- SF ClF A11A1 SF ClF B13B1 SF ClF A23A2 SF A’SF ClF A11A1 SF ClF A12A1 SF ClF A 1g SF ClF F axial draws more electron density than F equatorial does 2. F atoms in SF n draw more electron density than those in ClF n + XF 3 ( 2 A ’ ) F equatorial F axial F axial  RPB F equatorial  CB

Bond Energies of the Ground state ClF n + in Comparison with SF n (n=1-6) 1. The bond energies of ClF n + also exhibit the oscillating trend as seen in SF n. 2. The formation of ClF 3 + and ClF 5 + involves the recoupled pair bond. Both species are weakly bound with respect to ClF n F. Energy/eV n RCCSD(T)/AVTZ, Zero Point Energy Correction B3LYP/AVTZ Decouple the 3p 2 Decouple the 3s 2

Summary I  Because Cl has larger nuclear charge than S, it holds the electrons more tightly than S. In the case of the ClF n +, the positive charge on Cl is even larger. Thus the central atom holds the electrons even more tightly. This makes it even harder for F to withdraw electron density from Cl.

ClF n - : Predictions and Results ClF - ( 2  + ) ClF 2 - ( 2 A 1 )ClF 3 - ( 2 A 1 )ClF 4 - ( 1 A 1 )ClF 5 - ( 2 A 1 )ClF 6 - ( 1 A 1 ) ClF - ( 2  + ) ClF 2 - ( 2 A 1 )ClF 3 - ( 2 A 1 )ClF 4 - ( 1 A 1 )ClF 5 - ( 2 A 1 )ClF 6 - ( 1 A 1 ) ClF - ClF 2 - ClF 3 - ClF 4 - ClF 5 - ClF 6 - R ax R eq A T

Bond Energies (BDE) of ClF n - (n=1-6) Energy/eV n RCCSD(T)/AVTZ Zero Point Energy Correction B3LYP/AVTZ Decouple the 3p 2 Again, the oscillating trend can be explained by RPB

Ionization Energies (IE) and Electron Affinities (EA) of ClF n species (n=0-6) Energy/eV n 1. The IE of F is much higher than the ones of the ClF n species. 2. The EA of F, however, is lower than the ones of the open shell species ClF 2, ClF 4, and ClF 6, as well as the close shell ClF 5.

Summary II  Recoupled pair bonding is capable to predict the structures and energetics of the ground states as well as the excited states of SF n and ClF n +/0/-. Because of the positive charge, the lone pair electrons in Cl are much harder to be decoupled than the ones in the S. The bond energies of ClF n + are much smaller than the analogous SF n species. (ClF n - should be similar to ArF n. Research on ArF n is in progress.)  IE and EA of the ClF n species also exhibit oscillating trends as seen in the bond energies of ClF n and SF n.

Acknowledgment  Funded by the Distinguished Chair for Research Excellence in Chemistry at the University of Illinois at Urbana-Champaign.  Dunning Group: Thom. H. Dunning, Jr., David E. Woon, Jeff Leiding, Beth Lindquist, Lu Xu and Tyler Takeshita

SF n : Results I (n=1-3) SF 3 ( 2 A’)SF 2 ( 1 A 1 ) SF 2 ( 3 B 1 ) SF 2 ( 3 A 2 ) SF( 4  – ) SF( 2  ) RCCSD(T)/AVTZ results without ZPE correction Bond lengths in Å; Bond Energy in eV covalent w/antibonding e - hypervalent w/rearrangement 1.72 F FF  S F S F S  FF S FF S    F F S

ClF n + : Results I (n=1-3) F3 F1 F  Cl F Cl F Cl  FF Cl FF 2 1A11A1 3B13B1 2A’2A’   RCCSD(T)/AVTZ results without ZPE correction Bond lengths in Å; Bond Energy in eV 44 covalent w/antibonding e - hypervalent w/rearrangement The structures and states of ClF n + are similar to the structure of the corresponding isoelectronic SF n species, except for ClF 2 +, no stable 3 A 2 state was found. 3A23A2 Not Stable

XF n (X=S, Cl + ), (n=4-6) covalent w/antibonding e - hypervalent w/rearrangement XF 4 ( 1 A 1 )XF 5 ( 2 A 1 ) XF 6 ( 1 A 1g ) XF 3 ( 2 A 1 ) SF 5 ( 2 A 1 ) SF 3 ( 2 A’) SF 4 ( 1 A 1 ) SF 6 ( 1 A 1g ) ClF 3 + ( 2 A 1 )   FF FF 1A11A1 2A12A1 1 A 1g Cl FF FF F FF FF F F  RCCSD(T)/AVTZ results without ZPE correction, Bond lengths in Å; Bond Energy in eV/mol   

Bond Energies (BDE) of ClF n - (n=1-6) n BE Difference EA(ClF n )-EA(F) The difference ≈ the difference of electron affinities between the ClF n and F. 2. For n=2 and 4, the anions tend to dissociate to the close shell ClF or ClF 3 species because EA(ClF,ClF 3 ).< EA(F). Energy/eV n RCCSD(T)/AVTZ Zero Point Energy Correction B3LYP/AVTZ

Ionization Energy of ClF ClF + ( 2  ) ClF + ( 4    12.58eV 10.21eV 12.69eV MRCI+Q/AVTZ results without ZPE correction

Ionization Energy of ClF 2 ClF 2 + ( 1 A 1 ) ClF 2 + ( 3 B 1 ) 10.65eV 12.43eV 12.26eV 9.90eV RCCSD(T)/AVTZ results without ZPE correction