Temperature effects on prevalent structures of hydrated Fe+ complexes: Infrared spectroscopy and DFT calculations of Fe+(H2O)n (n = 3-8)

Kazuhiko Ohashi, Jun Sasaki, Gun Yamamoto, Ken Judai, Nobuyuki Nishi, Hiroshi Sekiya

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Hydrated Fe+ ions are produced in a laser-vaporization cluster source of a triple quadrupole mass spectrometer. The Fe+(H2O)n (n = 3-8) complexes are mass-selected and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region. Density functional theory (DFT) calculations are also carried out for analyzing the experimental IR spectra and for evaluating thermodynamic quantities of low-lying isomers. Solvation through H-bonding instead of direct coordination to Fe+ is observed already at n = 3, indicating the completion of the first hydration shell with two H2O molecules. Size dependent variations in the spectra for n = 5-7 provide evidence for the second-shell completion at n = 6, where a linearly coordinated Fe+(H2O)2 subunit is solvated with four H2O molecules. Overall spectral features for n = 3-8 agree well with those predicted for 2-coordinated structures. DFT calculations predict that such 2-coordinated structures are lowest in energy for smaller n. However, 4-coordinated isomers are predicted to be more stable for n = 7 and 8; the energy ordering is in conflict with the IR spectroscopic observation. Examination of free energy as a function of temperature suggests that the ordering of the isomers at warmer temperatures can be different from the ordering near 0 K. For n = 7 and 8, the 4-coordinated isomers should be observed at low temperatures because they are lowest in enthalpy. Meanwhile, outer-shell waters in the 2-coordinated structures are bound less rigidly; their contribution to entropy is rather large. The 2-coordinated structures become abundant at warmer temperatures, owing to the entropy effect.

Original languageEnglish
Article number214307
JournalJournal of Chemical Physics
Volume141
Issue number21
DOIs
Publication statusPublished - Dec 7 2014

Fingerprint

Isomers
Thermal effects
Density functional theory
temperature effects
Infrared spectroscopy
isomers
infrared spectroscopy
density functional theory
Infrared radiation
Entropy
entropy
Photodissociation
Temperature
Molecules
Solvation
Mass spectrometers
Vaporization
Hydration
photodissociation
mass spectrometers

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Temperature effects on prevalent structures of hydrated Fe+ complexes : Infrared spectroscopy and DFT calculations of Fe+(H2O)n (n = 3-8). / Ohashi, Kazuhiko; Sasaki, Jun; Yamamoto, Gun; Judai, Ken; Nishi, Nobuyuki; Sekiya, Hiroshi.

In: Journal of Chemical Physics, Vol. 141, No. 21, 214307, 07.12.2014.

Research output: Contribution to journalArticle

@article{c5061d16a7d64fbc8f4f57867ae17280,
title = "Temperature effects on prevalent structures of hydrated Fe+ complexes: Infrared spectroscopy and DFT calculations of Fe+(H2O)n (n = 3-8)",
abstract = "Hydrated Fe+ ions are produced in a laser-vaporization cluster source of a triple quadrupole mass spectrometer. The Fe+(H2O)n (n = 3-8) complexes are mass-selected and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region. Density functional theory (DFT) calculations are also carried out for analyzing the experimental IR spectra and for evaluating thermodynamic quantities of low-lying isomers. Solvation through H-bonding instead of direct coordination to Fe+ is observed already at n = 3, indicating the completion of the first hydration shell with two H2O molecules. Size dependent variations in the spectra for n = 5-7 provide evidence for the second-shell completion at n = 6, where a linearly coordinated Fe+(H2O)2 subunit is solvated with four H2O molecules. Overall spectral features for n = 3-8 agree well with those predicted for 2-coordinated structures. DFT calculations predict that such 2-coordinated structures are lowest in energy for smaller n. However, 4-coordinated isomers are predicted to be more stable for n = 7 and 8; the energy ordering is in conflict with the IR spectroscopic observation. Examination of free energy as a function of temperature suggests that the ordering of the isomers at warmer temperatures can be different from the ordering near 0 K. For n = 7 and 8, the 4-coordinated isomers should be observed at low temperatures because they are lowest in enthalpy. Meanwhile, outer-shell waters in the 2-coordinated structures are bound less rigidly; their contribution to entropy is rather large. The 2-coordinated structures become abundant at warmer temperatures, owing to the entropy effect.",
author = "Kazuhiko Ohashi and Jun Sasaki and Gun Yamamoto and Ken Judai and Nobuyuki Nishi and Hiroshi Sekiya",
year = "2014",
month = "12",
day = "7",
doi = "10.1063/1.4902408",
language = "English",
volume = "141",
journal = "Journal of Chemical Physics",
issn = "0021-9606",
publisher = "American Institute of Physics Publising LLC",
number = "21",

}

TY - JOUR

T1 - Temperature effects on prevalent structures of hydrated Fe+ complexes

T2 - Infrared spectroscopy and DFT calculations of Fe+(H2O)n (n = 3-8)

AU - Ohashi, Kazuhiko

AU - Sasaki, Jun

AU - Yamamoto, Gun

AU - Judai, Ken

AU - Nishi, Nobuyuki

AU - Sekiya, Hiroshi

PY - 2014/12/7

Y1 - 2014/12/7

N2 - Hydrated Fe+ ions are produced in a laser-vaporization cluster source of a triple quadrupole mass spectrometer. The Fe+(H2O)n (n = 3-8) complexes are mass-selected and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region. Density functional theory (DFT) calculations are also carried out for analyzing the experimental IR spectra and for evaluating thermodynamic quantities of low-lying isomers. Solvation through H-bonding instead of direct coordination to Fe+ is observed already at n = 3, indicating the completion of the first hydration shell with two H2O molecules. Size dependent variations in the spectra for n = 5-7 provide evidence for the second-shell completion at n = 6, where a linearly coordinated Fe+(H2O)2 subunit is solvated with four H2O molecules. Overall spectral features for n = 3-8 agree well with those predicted for 2-coordinated structures. DFT calculations predict that such 2-coordinated structures are lowest in energy for smaller n. However, 4-coordinated isomers are predicted to be more stable for n = 7 and 8; the energy ordering is in conflict with the IR spectroscopic observation. Examination of free energy as a function of temperature suggests that the ordering of the isomers at warmer temperatures can be different from the ordering near 0 K. For n = 7 and 8, the 4-coordinated isomers should be observed at low temperatures because they are lowest in enthalpy. Meanwhile, outer-shell waters in the 2-coordinated structures are bound less rigidly; their contribution to entropy is rather large. The 2-coordinated structures become abundant at warmer temperatures, owing to the entropy effect.

AB - Hydrated Fe+ ions are produced in a laser-vaporization cluster source of a triple quadrupole mass spectrometer. The Fe+(H2O)n (n = 3-8) complexes are mass-selected and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region. Density functional theory (DFT) calculations are also carried out for analyzing the experimental IR spectra and for evaluating thermodynamic quantities of low-lying isomers. Solvation through H-bonding instead of direct coordination to Fe+ is observed already at n = 3, indicating the completion of the first hydration shell with two H2O molecules. Size dependent variations in the spectra for n = 5-7 provide evidence for the second-shell completion at n = 6, where a linearly coordinated Fe+(H2O)2 subunit is solvated with four H2O molecules. Overall spectral features for n = 3-8 agree well with those predicted for 2-coordinated structures. DFT calculations predict that such 2-coordinated structures are lowest in energy for smaller n. However, 4-coordinated isomers are predicted to be more stable for n = 7 and 8; the energy ordering is in conflict with the IR spectroscopic observation. Examination of free energy as a function of temperature suggests that the ordering of the isomers at warmer temperatures can be different from the ordering near 0 K. For n = 7 and 8, the 4-coordinated isomers should be observed at low temperatures because they are lowest in enthalpy. Meanwhile, outer-shell waters in the 2-coordinated structures are bound less rigidly; their contribution to entropy is rather large. The 2-coordinated structures become abundant at warmer temperatures, owing to the entropy effect.

UR - http://www.scopus.com/inward/record.url?scp=84918592717&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84918592717&partnerID=8YFLogxK

U2 - 10.1063/1.4902408

DO - 10.1063/1.4902408

M3 - Article

AN - SCOPUS:84918592717

VL - 141

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 21

M1 - 214307

ER -