the search for an observable helium complex adrian m. gardner, timothy g. wright and corey j. evans
DESCRIPTION
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, Frenking, G. et al., 1988, 110, Frenking, G. et al., J. Phys. Chem. 1989, 93, Frenking, G., Cremer, D., Structure and Bonding, 1990, 73, Frenking, G. et al., J. Am. Chem. Soc., 1990, 112, Koch, W. et al., Chem. Phys. Lett. 1986, 132, 330 The coinage metal halide complexes appear to have these requirements.TRANSCRIPT
The Search for an Observable Helium
Complex
Adrian M. Gardner, Timothy G. Wright and Corey J. Evans
Metal Rare Gas Interactions
Several studies have shown evidence of the formation of partial covalent bonds between Xe and metals.
Gerry and co-workers1-3 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, 170003 Cooke, S.A., Gerry, M.C.L.., Phys. Chem. Chem. Phys., 2004, 13, 3248
But what about He and Ne?In the 1980s Frenking and coworkers4-8 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–CC2+ He–BCH He–BeO
4. Koch, W. et al, J. Am. Chem. Soc., 1987, 109, 5917 5. Frenking, G. et al., 1988, 110, 80076. Frenking, G. et al., J. Phys. Chem. 1989, 93, 3397 7. Frenking, G., Cremer, D., Structure and Bonding, 1990, 73, 178. 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.
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
Geometries and Dissociation EnergiesSpecies r(RG–M) / pm r(M–F) / pm Dissociation Energy
(De)CBS Limit / kJ mol-1
He–CuF 167.6 173.6 27.2
He–AgF 217.3 197.2 5.63
He–AuF 184.0 190.5 25.6
Ne–CuF 220.5 174.3 11.9
Ne–AgF 273.0 197.9 4.02
Ne–AuF 245.6 191.9 10.1
Ar–CuF 224.6 174.3 47.8
Ar–AgF 258.7 197.0 24.1
Ar–AuF 240.8 191.5 54.3
Geometries and Dissociation EnergiesSpecies r(RG–M) / pm r(M–F) / pm Dissociation Energy
(De)CBS Limit / kJ mol-1
He–CuF 167.6 173.6 27.2
He–AuF 184.0 190.5 25.6
Geometries and Dissociation EnergiesSpecies r(RG–M) / pm r(M–F) / pm Dissociation Energy
(De)CBS Limit / kJ mol-1
He–CuF 167.6 173.6 27.2
He–AgF 217.3 197.2 5.63
He–AuF 184.0 190.5 25.6
Geometries and Dissociation EnergiesSpecies r(RG–M) / pm r(M–F) / pm Dissociation Energy
(De)CBS Limit / kJ mol-1
He–CuF 167.6 173.6 27.2
He–AgF 217.3 197.2 5.63
He–AuF 184.0 190.5 25.6
Ne–CuF 220.5 174.3 11.9
Ne–AgF 273.0 197.9 4.02
Ne–AuF 245.6 191.9 10.1
Geometries and Dissociation EnergiesSpecies r(RG–M) / pm r(M–F) / pm Dissociation Energy
(De)CBS Limit / kJ mol-1
He–CuF 167.6 173.6 27.2
He–AgF 217.3 197.2 5.63
He–AuF 184.0 190.5 25.6
Ne–CuF 220.5 174.3 11.9
Ne–AgF 273.0 197.9 4.02
Ne–AuF 245.6 191.9 10.1
Ar–CuF 224.6 174.3 47.8
Ar–AgF 258.7 197.0 24.1
Ar–AuF 240.8 191.5 54.3
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 0.07M 0.83 0.74 0.85 0.81 0.68 0.60F -0.83 -0.80 -0.85 -0.83 -0.68 -0.67
Analysis of Bonding within the RG-MF complexes
40
2
0 84 rq
E effind
60
2
0 442
rEind
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
Analysis of Bonding within the RG-MF complexes
Complex μ/μind qeff/μind De
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
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
Comparison of the bonding of He-MF and He-MCl
Species r(RG–M) / pm r(M–X) / pm Dissociation Energy (De)CBS Limit / kJ mol-1
He–CuF 167.6 173.6 27.2He–CuCl 175.3 205.6 17.8He–AgF 217.3 197.2 5.63He–AgCl 226.2 228.3 4.52
He–AuF 184.0 190.5 25.6He–AuCl 197.4 220.8 13.6
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.