infrared spectra of anionic coinage metal-water complexes j. mathias weber jila and department of...
DESCRIPTION
Motivation Metal atoms and clusters deposited on surfaces with anionic defect sites have interesting catalytic properties. Example: Au n (-) + ½ O 2 + CO CO 2 A. Cho, Science 299, 1684 (2003)TRANSCRIPT
Infrared Spectra of Anionic Coinage Metal-Water
ComplexesJ. Mathias Weber
JILA and Department of Chemistry and Biochemistry
University of Colorado at Boulder
Dramatis Personae
€€€ DFG (Emmy-Noether-Program), Universität Karlsruhe
Experiment:Holger Schneider (now CU Boulder)
Calculations:A. Daniel Boese(Institute for Nanotechnology,Forschungszentrum Karlsruhe,Germany)
Motivation
Metal atoms and clusters deposited on surfaces with anionic defect sites have interesting catalytic properties.
Example:
Aun(-) + ½ O2 + CO CO2
A. Cho, Science 299, 1684 (2003)
Motivation
Metal atoms and clusters deposited on surfaces with anionic defect sites have interesting catalytic properties.
The presence of water has been seen to strongly influence the catalytic process.
How do water molecules and noble metal anions interact?
Possible Approach: Vibrational Spectroscopy
OH groups equivalent
symmetric and antisymmetric stretch vibrations in free H2O:
3657 cm-1
3756 cm-1
Possible Approach: Vibrational Spectroscopy
OH groups equivalent
symmetric and antisymmetric stretch vibrations in free H2O:
3657 cm-1
3756 cm-1
in clusters: H bonds with ion and other ligands
stretching of the H bonding OH groups breaking of symmetry red shift of H bonded oscillators
Possible Approach: Vibrational Spectroscopy
OH groups equivalent
symmetric and antisymmetric stretch vibrations in free H2O:
3657 cm-1
3756 cm-1
Experimental Method: IR Photodissociation
[A·B]- [A]- + Bh
M-·H2O·Arn + h
[M-·H2O·Arn ]*
M-·H2O·Arm + (n-m) Ar
Experimental Setup: Reflectron TOF-MS
2100 – 3800 cm-1
1-10 mJ / 5 nsIR-OPO/OPA
Nd:YAG
qmt
J. M. Weber, Rev. Sci. Instrum. 76 (2005) 043301
Possible structural motifs: single or double ionic H bond
Single Ionic H Bond Double Ionic H Bond
How will anions interact with H2O? Intuitive approach
free OH oscillator (F band)
F band: between s and as of H2O ca. 3700 cm-1
Spectra of SIHB complexes:
How will anions interact with H2O? Intuitive approach
free OH oscillator (F band)
OH oscillator in H bond(IHB band)
Spectra of SIHB complexes:
How will anions interact with H2O? Intuitive approach
F band: between s and as of H2O ca. 3700 cm-1
IHB band:red shifted against F band
Example: Cl-·H2O·Arn
How will anions interact with H2O? Intuitive approach
Kelley et al., Chem. Phys. Lett. 327 (2000) 1
Example: Cl-·H2O·Arn
F band
How will anions interact with H2O? Intuitive approach
Kelley et al., Chem. Phys. Lett. 327 (2000) 1
Example: Cl-·H2O·Arn
F band
IHB band
How will anions interact with H2O? Intuitive approach
Kelley et al., Chem. Phys. Lett. 327 (2000) 1
Example: Cl-·H2O·Arn
F band
IHB band
Fermi resonance of IHB withbend overtone,combination band with ion-moleculestretch vibration
Kelley et al., Chem. Phys. Lett. 327 (2000) 1
How will anions interact with H2O? Intuitive approach
s and as of H2Ored shifted againstpositions in free H2O
Example: SO2-·H2O
Spectra of DIHB complexes
Woronowicz et al., J. Phys. Chem. A 2002, 106, 7086
How will anions interact with H2O? Intuitive approach
So far: SIHB motif for all complexes with atomic anions
Expectation: SIHB motif
How will anions interact with H2O? Intuitive approach
13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0
200
400
600
8001000
2000
4000
re
d sh
ift [c
m-1]
proton affinity [eV]
I
Br
ClNO2
O2
F
OH
Red shift and anion proton affinity (SIHB motif)
13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0
200
400
600
8001000
2000
4000
re
d sh
ift [c
m-1]
proton affinity [eV]
I
Br
ClNO
2
O2
F
OH
AuAg
Cu
Expectation for IHB bands of M-·H2O in SIHB configuration
3000 3100 3200 3300 3400 3500 3600 3700
F
F
Ag
CuB
SIHB
SIHB
B
photon energy [cm-1]
phot
ofra
gmen
t act
ion
B
Au
F
SIHB
IR spectra of M-·H2O
M-·H2O·Ar2 + h M-·H2O + 2 Ar
3000 3100 3200 3300 3400 3500 3600 3700
F
F
Ag
CuB
SIHB
SIHB
B
photon energy [cm-1]
phot
ofra
gmen
t act
ion
B
Au
F
SIHB
Expectation for IHB:
Cu > Ag > Au
IR spectra of M-·H2O
3000 3100 3200 3300 3400 3500 3600 3700
F
F
Ag
CuB
SIHB
SIHB
B
photon energy [cm-1]
phot
ofra
gmen
t act
ion
B
Au
F
SIHB
Result:Au > Cu > Ag
Moreover: F band red shifted !!!
IR spectra of M-·H2O
Expectation for IHB:
Cu > Ag > Au
13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0
200
400
600
8001000
2000
4000
re
d sh
ift [c
m-1]
proton affinity [eV]
I
Br
ClNO2
O2
F
OH
OCSSO2
Au
Ag
Cu
Comparing SIHB / DIHB data
SIHB
DIHB
Potential of the water rocking motion
Calculated barriers(CCSD(T)/aug-pc-2;ECP-MCDF-aug-pVTZ):
• Au-·H2O: 42 meV• Ag-·H2O: 16 meV• Cu-·H2O: 17 meV
Very low barriers! Cl-·H2O: 80 meV
0 20 40 60 80 100
0
10
20
30
40
50
60
zero pointcorrected
BO-surface
E [m
eV]
Potential of the water rocking motion
Double harmonic oscillator (Schrödinger Applet)
high barrier
Potential of the water rocking motion
Double harmonic oscillator (Schrödinger Applet)
high barrier low barrier
Asymmetric DIHB Structure
Cs equilibrium structure, but complex explores geometries near C2v transition state due to zero point motion
„free“ OH group contributes to binding
red shift of F band
red shift of IHB band reduced
New H-bonding behavior: dynamic asymmetric DIHB due to ground state zero point motion
H. Schneider, A. D. Boese, J. M. Weber, J. Chem. Phys. 123, 084307 (2005)
3300 3400 3500 3200 3300 34003100 3200 3300
Ar p
redi
ssoc
iatio
n yi
eld
[arb
. uni
ts]
n = 2n = 2
n = 1n = 1
n = 1
n = 2
Au Cu
photon energy [cm-1]
Ag
Argon Effects
