1. Infrared Spectroscopy of Doubly-Charged Metal-Water Complexes
Biswajit Bandyopadhyay, Prosser D. Carnegie and Michael A. Duncan
Department of Chemistry, University of Georgia, Athens, GA, 30602
U. S. Department of Energy

2. Motivation Understanding solvation at the molecular level
Metal-cation solvation plays key role in many chemical and biological processes
Most work has been performed on singly charged metal-water complexes
J. Phys. Chem. 2008, 112, 6237

3. Previous Work
First studies focused on bulk phase measurements of multiply charged metal complexes
Difficulty in producing stable species in the gas phase
Generated ions by electrospray and analyzed with mass spectrometric methods (Kebarle, Posey, Williams, Metz, Schwarz, etc.)
Electronic Spectroscopy performed by Metz and coworkers, Stace and coworkers
Infrared spectroscopy by Williams and coworkers, Duncan and coworkers

4. Experimental

5. Mass spectrum of the ions produced in the laser vaporization cluster source
Density of doubly charged ions is
much less than singly charged ions.
This is also seen with other sources.

6. Metal Ion-Water Complexes: M2+(H2O)
M IP(eV) nd IP(eV) Cr Mn Sc V
IP (H2O) eV
Asymptotically Stable
Asymptotically Unstable
Asymptotically unstable doubly charged metal-water
complexes are produced by carefully adjusting the
vaporization laser power, laser timing with respect to the
gas pulse, alignment of the laser to the metal rod and
gas pulse width
N. R. Walker, G. A. Grieves, J. B. Jaeger, R. S. Walters and M. A. Duncan. Int. J. Mass. Spec. 2003, 228, 285

7. Binding Energy (D0; kcal/mol) vs Photon Energy Mn+-H2O Mn+-Ar
Cr (10,807 cm-1)a (2338 cm-1) c
Cr (29,510 cm-1)b (13,050 cm-1) d
H2O O-H sym 3657 cm-1 O-H asym cm-1
vibrations H-O-H bend cm-1
IR Photon
loss of argon Ar M+
a. Armentrout and coworkers, JACS 1994, 116, c. Brucat and coworkers, Chem. Phys. Lett. 1991, 177, 380.
b. Bock and coworkers, Inorg. Chem. 1998, 372, 4425

8. Red Shift in O-H Stretches
The HOMO of water has partial
bonding character.
Polarization of the electron due to
metal cation removes the electron
density from the O-H bond –Red shift
Intensity Pattern
The intensity ratio of symmetric and
asymmetric stretches 1: 18 for water molecule.
Combination band
Asymmetric Stretch
Asymmetric Stretch-perpendicular
type vibration- less change in
dynamical dipole moment than the
symmetric stretch
Symmetric Stretch-parallel type
vibration- Involves greater change in
dynamical dipole moment-gains
greater intensity
Symmetric Stretch C2

9. Comparison of red shifts and intensity pattern of O-H stretches of the M+(H2O) and M2+(H2O) complexes
Red shift is larger for metal dication-
water complex as polarization is more
Symmetric Stretch
Asymmetric Stretch C2
Intensity ratio of sym. and asym. stretches is ~2:1 for the metal dication-water complex 9

10. Partially Resolved Rotational
structure- gives geometry of the
complex and temperature.

11. 11

12. Hydroxide formation
Sc3+(OH-)H(Ar)6 12

13. Infrared Spectra of Doubly Charged Vanadium-Water-Argon complexes
V3+(OH-)H(Ar)6

14. Conclusions Acknowledgement
IRPD spectra for singly and doubly charged metal water complexes obtained
OH stretching frequencies are red shifted
Symmetric stretch gains IR intensity relative to asymmetric stretch
Sifts in band positions and IR intensities greater for dications
Acknowledgement
Michael A. Duncan
DOE for funding