1. The Search for an Observable Helium Complex Adrian M. Gardner, Timothy G. Wright and Corey J. Evans

2. Metal Rare Gas Interactions Several studies have shown evidence of the formation of partial covalent bonds between Xe and metals. Gerry and co-workers 1-3 have studied the RG–MX (RG = Ar, Kr, Xe; M = Cu, Ag, Au; X = F, Cl, Br) using microwave spectroscopy. One could expect that the interactions between RG atoms and metal cations would be purely physical. The overall “strength” of the bond between the metal and RG is approximately proportional to the polarizability of the RG. 1 Michaud, J.M., Gerry, M.C.L, J. Am. Chem. Soc., 2006, 128, 7613 2 Cooke, S.A., Gerry, M.C.L, J. Am. Chem. Soc., 2004, 126, 17000 3 Cooke, S.A., Gerry, M.C.L.., Phys. Chem. Chem. Phys., 2004, 13, 3248

3. But what about He and Ne? In the 1980s Frenking and coworkers 4-8 proposed a donor- acceptor model which demonstrated He could form stable chemical compounds with another species (X) providing that there is; A suitable s- or σ -hole. A sufficiently high charge on X. Several possible species have been proposed; 8,9 He–CC 2+ He–BCH He–BeO 4. Koch, W. et al, J. Am. Chem. Soc., 1987, 109, 5917 5. Frenking, G. et al., 1988, 110, 8007 6. Frenking, G. et al., J. Phys. Chem. 1989, 93, 3397 7. Frenking, G., Cremer, D., Structure and Bonding, 1990, 73, 17 8. Frenking, G. et al., J. Am. Chem. Soc., 1990, 112, 4240 9. Koch, W. et al., Chem. Phys. Lett. 1986, 132, 330 The coinage metal halide complexes appear to have these requirements.

4. RG-MX (M = Cu, Ag, Au; X= F, Cl; RG = He, Ne, Ar) Geometry optimizations at the CCSD/aVDZ, CCSD/aVTZ and CCSD/aVQZ levels of theory. ECP10MDF, ECP28MDF and ECP60MDF with the aVXZ-PP basis sets were used for Cu, Ag and Au respectively. Energy calculations at the CCSD(T)/aVQZ and CCSD(T)/aV5Z. Extrapolated the energy to the complete basis set limit. All valence electrons of the RG’s, F and Cl as well as non-ECP electrons of the metals were included in the correlation treatment. 10. Evans, C. J. et al., J. Phys. Chem. A., 2010, 114, 4446

5. Geometries and Dissociation Energies Speciesr(RG–M) / pmr(M–F) / pm Dissociation Energy (D e ) CBS Limit / kJ mol -1 He–CuF167.6173.627.2 He–AgF217.3197.25.63 He–AuF184.0190.525.6 Ne–CuF220.5174.311.9 Ne–AgF273.0197.94.02 Ne–AuF245.6191.910.1 Ar–CuF224.6174.347.8 Ar–AgF258.7197.024.1 Ar–AuF240.8191.554.3

6. Geometries and Dissociation Energies Speciesr(RG–M) / pmr(M–F) / pm Dissociation Energy (D e ) CBS Limit / kJ mol -1 He–CuF167.6173.627.2 He–AuF184.0190.525.6

7. Geometries and Dissociation Energies Speciesr(RG–M) / pmr(M–F) / pm Dissociation Energy (D e ) CBS Limit / kJ mol -1 He–CuF167.6173.627.2 He–AgF217.3197.25.63 He–AuF184.0190.525.6

8. Geometries and Dissociation Energies Speciesr(RG–M) / pmr(M–F) / pm Dissociation Energy (D e ) CBS Limit / kJ mol -1 He–CuF167.6173.627.2 He–AgF217.3197.25.63 He–AuF184.0190.525.6 Ne–CuF220.5174.311.9 Ne–AgF273.0197.94.02 Ne–AuF245.6191.910.1

9. Geometries and Dissociation Energies Speciesr(RG–M) / pmr(M–F) / pm Dissociation Energy (D e ) CBS Limit / kJ mol -1 He–CuF167.6173.627.2 He–AgF217.3197.25.63 He–AuF184.0190.525.6 Ne–CuF220.5174.311.9 Ne–AgF273.0197.94.02 Ne–AuF245.6191.910.1 Ar–CuF224.6174.347.8 Ar–AgF258.7197.024.1 Ar–AuF240.8191.554.3

10. Analysis of Bonding within the RG-MF complexes Natural Bond Order (NBO) analysis was carried out using the CCSD density using the aVTZ basis set in G03. He+CuF HeCuF He+AgF HeAgF He+AuF HeAuF He 0.00 0.06 0.00 0.02 0.00 0.07 M 0.83 0.74 0.85 0.81 0.68 0.60 F -0.83 -0.80 -0.85-0.83 -0.68 -0.67

11. Analysis of Bonding within the RG-MF complexes The inductive interactions present between the RG and the MF can be approximated by; 11 11. Thomas, J. M. et al., J. Am. Chem. Soc., 2004, 126, 1235

12. Analysis of Bonding within the RG-MF complexes Complex μ / μ ind q eff / μ ind D e He–CuF 3 9 27 He–AgF 1 3 6 He–AuF 1 2 26 He–Cu + - 10 11 He–Ag + - 4 5 He–Au + - 4 5 All values are in kJ mol -1

13. Analysis of Bonding within the RG-MF complexes The electronegativity of the F will pull electron density away from the metal atom. The HOMO-LUMO gap is smaller in the MF than in the M +. LUMO of AuF

14. Comparison of the bonding of He-MF and He-MCl Speciesr(RG–M) / pmr(M–X) / pm Dissociation Energy (D e ) CBS Limit / kJ mol -1 He–CuF167.6173.627.2 He–CuCl175.3205.6 17.8 He–AgF217.3197.25.63 He–AgCl226.2228.3 4.52 He–AuF184.0190.525.6 He–AuCl197.4220.813.6

15. Conclusions The dissociation energies of the He-MX are higher than the Ne- MX complexes. The dissociation energy of the He-MF complexes are higher than He-MCl complexes. Is the bonding in these species covalent? Potentially, the dissociation energies of the He-MX complexes are sufficiently high that these species may be observed experimentally.