Vibrational Spectroscopy and Theory of Fe+(CH4)(n) (n=1-4)

Citir M., Altinay G., AUSTEIN-MILLER G., Metz R. B.

JOURNAL OF PHYSICAL CHEMISTRY A, vol.114, no.42, pp.11322-11329, 2010 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 114 Issue: 42
  • Publication Date: 2010
  • Doi Number: 10.1021/jp104602k
  • Journal Name: JOURNAL OF PHYSICAL CHEMISTRY A
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.11322-11329
  • Abdullah Gül University Affiliated: No

Abstract

Vibrational spectra are measured for Fe+(CH4)n (n = 1−4) in the C−H stretching region (2500−3200 cm−1) using photofragment spectroscopy. Spectra are obtained by monitoring CH4fragment loss following absorption of one photon (for n = 3, 4) or sequential absorption of multiple photons (for n = 1, 2). The spectra have a band near the position of the antisymmetric C−H stretch in isolated methane (3019 cm−1), along with bands extending >250 cm−1 to the red of the symmetric C−H stretch in methane (2917 cm−1). The spectra are sensitive to the ligand configuration (η2 vs η3) and to the Fe−C distance. Hybrid density functional theory calculations are used to identify possible structures and predict their vibrational spectra. The IR photodissociation spectrum shows that the Fe+(CH4) complex is a quartet, with an η3 configuration. There is also a small contribution to the spectrum from the metastable sextet η3 complex. The Fe+(CH4)2 complex is also a quartet with both CH4 in an η3 configuration. For the larger clusters, the configuration switches from η3 to η2. In Fe+(CH4)3, the methane ligands are not equivalent. Rather, there is one short and two long Fe−C bonds, and each methane is bound to the metal in an η2 configuration. For Fe+(CH4)4, the calculations predict three low-lying structures, all with η2 binding of methane and very similar Fe−C bond lengths. No single structure reproduces the observed spectrum. The approximately tetrahedral C1 (4A) structure contributes to the spectrum; the nearly square-planar D2d (4B2) and the approximately tetrahedral C2 (4A) structure may contribute as well.

Vibrational spectra are measured for Fe+(CH4) (n = 1-4) in the C-H stretching region (2500-3200 cm(-1)) using photofragment spectroscopy. Spectra are obtained by monitoring CH4 fragment loss following absorption of one photon (for n = 3, 4) or sequential absorption of multiple photons (for n = 1, 2). The spectra have a band near the position of the antisymmetric C-H stretch in isolated methane (3019 cm(-1)), along with bands extending >250 cm(-1) to the red of the symmetric C-H stretch in methane (2917 cm(-1)). The spectra are sensitive to the ligand configuration (eta(2) vs eta(3)) and to the Fe-C distance. Hybrid density functional theory calculations are used to identify possible structures and predict their vibrational spectra. The IR photodissociation spectrum shows that the Fe+(CH4) complex is a quartet, with an eta(3) configuration. There is also a small contribution to the spectrum from the metastable sextet eta(3) complex. The Fe+(CH4)(2) complex is also a quartet with both CH4 in an eta(3) configuration. For the larger clusters, the configuration switches from eta(3) to eta(2). In Fe+(CH4)(3), the methane ligands are not equivalent. Rather, there is one short and two long Fe-C bonds, and each methane is bound to the metal in an eta(2) configuration. For Fe+(CH4)(4), the calculations predict three low-lying structures, all with eta(2) binding of methane and very similar Fe-C bond lengths. No single structure reproduces the observed spectrum. The approximately tetrahedral C-1 ((4)A) structure contributes to the spectrum; the nearly square-planar D-2d (B-4(2)) and the approximately tetrahedral C-2 ((4)A) structure may contribute as well.