Al_Benzene Reishus OH 2013

Report
Infrared Photodissociation Spectroscopy
of
Aluminum Benzene Cation Complexes
Nicki Reishus, Biswajit Bandyopadhyay and
Michael A. Duncan
Department of Chemistry, University of Georgia, Athens, GA 30602
www.arches.uga.edu/~maduncan/
[email protected]; [email protected]
Metal benzene sandwiches
•
1973 Nobel to Wilkinson and Fischer for work on organometallic
sandwiches1
Ferrocene
Wilkinson and Woodward
1952
Di-benzene chromium
E. O. Fischer
1955
1. Fischer, E. O.; Hafner, W. Z. Naturforsch. 1955, 10b, 665.
Previous work on metal-benzene ions:
•
Duncan group  electronic photodissociation1
•
Kaya and coworkers  multiple-decker sandwiches and photoelectron spectroscopy (PES) on
anions2
•
Lisy and coworkers infrared (IR)
spectroscopy in C–H stretch region
with alkali metals3
•
Duncan et al. FELIX in far IR and IR-OPO in mid IR on transition metals4
•
D. S. Yang group  ZEKE spectroscopy on transition metals5
1.
2.
3.
4.
5.
Willey, K. F.; Yeh, C. S.; Robbins, D. L.; Duncan, M. A., J. Phys. Chem. 1992, 96, 9106-9111.
Nakajima, A.; Kaya, K., J. Phys. Chem. A 2000, 104, 176-1913.
Cabarcos, O. M.; Weinheimer, C. J.; Lisy, J. M., J. Chem. Phys. 1999, 110, 8429-8435.
M.A. Duncan, Int. J. Mass Spectrom. 2008, 272, 99.
B. R. Sohnlein, Y. Lei and D.-S. Yang, J. Chem. Phys. 2007, 127, 114302/1-114302/10.
Previous work: OPO/OPA
ν +ν
19
8
ν20

•
OPO/OPA with argon tagging used for C–H
stretch region
•
Free benzene Fermi resonance1: 3048,
3079, 3101 cm-1
ν1+ν6+ ν19

+
V (bz)3
+
V (bz)2Ar
•
V+(bz)3 no Ar tagging needed, and free
benzene Fermi resonance observed
•
3rd
+
V (bz)Ar
benzene is external
2700
2800
2900
3000
3100
3200
3300
-1
cm
Jaeger, T. D.; Pillai, E. D.; Duncan, M. A., J. Phys. Chem. A 2004, 108,
6605-6610.
1. Snavely, D. L.; Walters, V.A.; Colson, S.D.; Wiberg, K. B., Chem. Phys. Lett. 1984, 103, 423-429.
Experimental
•
OPO/OPA range: 600-4500 cm-1
•
Binding energies  Al+(bz) = 35.2 kcal/mol1, Al+(bz)Ar = 0.8 kcal/mol (MP2/6-311+G** )
•
Theory: B3LYP/6-311+G**
Aluminum benzene mass spec:
1. Dunbar, R. C.; Klippenstein, S. J.; Hrusak, J.; Stockigt, D.; Schwarz, H. J. Am. Chem. Soc. 1996, 118, 5277-5283.
Al+(bz)Ar
673
•
750
 ν11 oop H-bend, 77
blue shift
•
990 cm-1 ν1 sym. C stretch, (not IR
active in free benzene)
cm-1
cm-1
•
1476 cm-1  ν19 in–plane C ring
distortion, indicator of charge transfer1,
10 cm-1 red shift
•
1643 cm-1  ν8 C ring stretch (not IR
active in free benzene), 33 cm-1 blue
shift
•
3033 cm-1  ν20 C–H stretch
•
3097, 3065 cm-1  Fermi resonance:
ν20 C–H stretch & ν8+ν19, ν1+ν6+ ν19,
respectively
•
730 993
1610
1481
990
1610
3079
3048 3101
3121
737
1479
Theory scaled for each mode
981
1. Chaquin, P.; Costa, D.; Lepetit, C.; Che, M. J. Phys.
Chem. A 2001 105, 4541-4545.
1486
van Heijnsbergen, D.;
Jaeger, T. D.; von
Helden, G.; Meijer,
G.; Duncan, M. A.,
Chem. Phys. Lett.
2002, 364, 345-351.
Al+(bz)2Ar
•
3079
 Fermi resonance caused
by addition of second benzene
•
1596 cm-1  ν8 ring stretch, goes from
33 cm-1 blue shift to 14 cm-1 red shift
•
1477 cm-1  ν19 in–plane C ring
distortion, 9 cm-1 red shift
•
719 cm-1  ν11 oop H-bend, 46 cm-1
blue shift, 31 cm-1 less than Al+(bz)Ar
•
Bond distance 2.5 Å  2.8 Å
cm-1
673
1486
1610
993
cm-1
3079
3048 3101
Where does a 2nd benzene go?
•
Al+  3s2
•
s orbital polarizable1
•
1st ligand polarizes s orbital1
e-
e-
Walters, R. S.; Brinkmann, N. R.; Schaefer, H. F.; Duncan,
M. A., J. Phys. Chem. A 2003, 107, 7396-7405.
1. Bauschlicher, Jr., C. W.; Partridges, H. J. Phys. Chem. 1991, 95, 9694-9698.
Al+(bz)3Ar
•
Fourth Fermi resonance disappears
•
1643 cm-1  ν8 ring stretch goes away
•
1478 cm-1  ν19 in–plane C ring distortion,
8 cm-1 red shift
•
723 cm-1  ν11 oop H-bend, 50 cm-1 blue
shift, 4 cm-1 blue shift from Al+(bz)2Ar
•
Theory indicates ν11 red shifts from
Al+(bz)Ar
•
Bond distance increases to 2.9 Å
673
993
1486
1610
?
3079
3101
3048
Vib. of external ligands are usually un-shifted
•
•
External ligands cause un-shifted ligand
peaks to appear
Free CO2 band
Coordinated CO2 band
But there is no evidence in Al+(bz)3Ar for
un-shifted bands
Ricks, A. M.; Brathwaite, A. D.; Duncan, M. A. J.
of Phys. Chem. A 2013 117 , 1001-1010.
Al+(bz)4
•
1481 cm-1  ν19 in–plane C ring
distortion, 5 cm-1 red shift
•
Theory predicts a wider ν11 peak due to a
4th external benzene
•
No ν11 cm-1 peak observed (likely
because of diss. energy)
•
Again no evidence of un-shifted bands
673
993
?
•
Different IR intensities for bonded vs
external bands?
1486
1610
3079
3048 3101
Spectra of Al+(bz)1-3Ar, Al+(bz)4 do not show evidence
for an external benzene
?
?
cm-1
Conclusions
•
Best quality IR spectra yet measured for a metal ion benzene system
•
ν19 shows there is not much charge transfer between the Al+ and benzene
•
Theory predicts a consistent red shift for the ~700 cm-1 band, but experiments
show a change in relative shift from red to blue
•
Theory does not predict the ν8 band
•
Coordination is not obvious from spectra
•
Theory shows a coordination of three
Binding energies: theory
Literature1
Binding energies B3LYP/
of ligand
6-311+G**
(kcal/mol)
MP2/
B97D/
6-311+G**
6-311+G**
Al+-Benzene
30.0
35.4
34.1
35 ±2
Al+-(Benzene)2
11.6
-
19.6
-
Al+-(Benzene)3
4.5
-
-
-
Al+-(Benzene)4
2.8
-
-
-
1. Dunbar, R. C.; Klippenstein, S. J.; Hrusak, J.; Stockigt, D.; Schwarz, H. J. Am. Chem. Soc. 1996, 118, 5277-5283.

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