Transcript osu06f.ppt
Experimental Rotational Spectra for MnRe(CO)10
and o-C6H4† Required Accurate theoretical
Calculations for Successful Analysis
STEPHEN KUKOLICH, Chemistry Dept., University of Arizona,
MICHAEL PALMER School of Chemistry, University of Edinburgh,
PETER GRONER, Chemistry, University of Missouri-Kansas City, and
CHAKREE TANJAROON, Chemistry, University of Alberta,
C1
C2
H1
b
C3
Mn
a
C6
Re
C4
C5
H2
† Measured at Harvard with Pat Thaddeus and Mike McCarthy
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Observing and Measuring the Rotational
Transition Frequencies was Difficult
B = 200.3687 MHz (187Re )
eQq(187Re) = 370.42(38) MHz
eQq(55Mn) = -16.52(5) MHz
Mn
Re
C1
C2
H1
b
C3
a
C4
H2
C5
C6
Normal Isotopomer transitions
were readily observed
13C Isotopomer lines often
obscured by other products of
Discharge (Shotgun effect)
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MnRe(CO)10
+ >Symmetric top with C4v symmetry
- >Combination of small B-values with two
quadrupoles resulted in congested and
difficult-to-assign spectra (J=11→ 12 and
12→ 13)
+ > Michael Palmer and Martyn Guest
(Edinburgh) calculated the eQq values
sufficiently accurately to allow
unambiguous assignments of the spectra
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Example Spectra for 8, and 10 MHz
“pieces” of the spectrum
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Pair of
measured
transitions
2000
Shots
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C4v symmetry
Only K=4n transitions
observed
Staggered or
Eclipsed? †
(S)
† F. A. Cotton, Austin 2004
(E)
(E)
Mn
Re
(S)
Mn
Re
xx
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Experimental and theoretical molecular parameters for Mn 187Re(CO)10 .
Calculated Values (B3LYP) from M. H. Palmer, et al. (J. Chem. Phys. 121, 7187
(2004)). B and eQq values in MHz.
187
Parameter
Mn
Re(CO)10
MICROWAVE
Mn187Re(CO)10
Mn187Re(CO)10
Calculated
Calculated
(STAGGERED)
(ECLIPSED)
MnRe(CO)10
X-ray1
eQq(55Mn)
-16.52(5)
5.87
0.68
-
eQq(187Re)
370.42(38)
310.11
327.6
-
B
200.36871(8)
188.77
178.40
204.2304
rMnRe (Å)
2.99
3.086 Å
3.224
2.909(1)
212(1)
199(1)
De(kJ/mol)
Calculated from the geometry
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A. L. Rheingold, W. K. Meckstroth, and D.P. Ridge, Inorg. Chem. 25, 3706-3707 (1986)
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The structure of o – benzyne and
vibrational averaging effects.
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1.
Spectra Measured on HARVARD FTMWS1
Discharge 0.5% BENZENE in NEON
Normal Isotopomer - 27 b-dipole transitions
13C - 12 b-dipole transitions
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D1 - 26 b-dipole transitions
D2 - 23 b-dipole transitions
13C (1) - 10 b-dipole transitions
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DIFFICULT
13C (3) - 9 b-dipole transitions
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To MEASURE
13C (5) - 10 b-dipole transitions
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S. G. Kukolich, M. C. McCarthy and P. Thaddeus, J. Phys. Chem.
108, 2645-2651, (2004)
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Search for 13C lines… in a sea of lines from other
radicals and molecules produced in the DISCHARGE.
WRONG
MOLECULE
GOOD
ONE
JUNK
C1
C2
H1
b
C3
a
C4
C6
C5
H2
kHz
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Least-squares structure fit
The inertial defect for the normal isotopomer of o-benzyne is
= ICC – IAA – IBB = 0.06935(1) amu Å2, consistent with a
PLANAR STRUCTURE.
This value is sufficiently large that when trying to fit the measured
A, B, and C rotational constants with a planar structure, some of
the deviations will be as large as 1 MHz.
EXPT
STANDARD DEVIATION
CALC.
DEV.
NORMAL A
6989.729
6989.915
-0.186
FOR FIT = 1.05 MHz
B
5706.806
5706.891
-0.085
Experimental errors
are < 2 kHz!
C
3140.371
3141.789
-1.418
13C1 A
6859.730
6859.886
-0.155
B
5679.516
5679.369
0.147
C
3105.740
3107.029
-1.289
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Least-squares fit to determine the structure
Most of the same vibrational averaging effects which
contribute to the differences between the r0 and re
coordinates, will also contribute to this inertial defect.
Problem 1. We are trying to fit a PLANAR, (re ) structure
to EXPERIMENTAL A, B, and C which have non-zero
inertial defect, (characteristic of the r0 coordinates )
Problem 2. The r0 coordinates are different for each of
the measured isotopomers
SOLUTION: Find the ak, vibration-rotation constants, so
we fit the re structure, same for all isotopomers
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VIBRATIONAL AVERAGING EFFECTS – RELATED TO
VIBRATION-ROTATION INTERACTION CONSTANTS k
a
A rotational constant for the GROUND VIBRATIONAL
STATE, Bo, is related to the EQUILIBRIUM rotational
constant, Be by: (summed over k vibrational states)
αα
o
B
B
αα
e
1
2
αk
k
The corresponding relation for MOMENTS OF
INERTIA is:
I
αα
o
I
αα
e
1
2
C1
C2
kαα
H1
b
C3
a
C4
C6
C5
H2
k
and the INERTIAL DEFECT is:
Δo I occ I oaa I obb
Values for these ak were calculated by Peter Groner1,
University of Missouri
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Final Structure of o-benzyne
1.255
1.383
127
H1
C2
o
127
C3
Now the fit is MUCH improved ( s < 30 kHz)
C1
o
o
b
1.080
a
111
r(C1-C2) for HCCH =1.203 Å
r(C1-C2) for H2CCH2 =1.332 Å
C6
o
122
1.403
o
119
H2
C4
C5
1.405
1.082
r(C2-C3) for benzene =1.3914 Å
r(C2-C3), NMR value → 1.24(2) Å
Grant, Michl, et al.
P. Groner and S. G. Kukolich, J. Mol. Struct. 780-781, 178 (2006)
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The re structure of o-benzyne
Structural
parameter
re
MP2/
6-31G(d)
(Distances r in Å)
rs /
Kraitchman
B3LYP/
631G(d,p)
BPW9
1/ ccpVDZ
Ref.
This work This work [a]
[b]
[c]
r(C1-C2)
1.255(3)
1.268
1.255(8)
1.251
1.266
r(C2-C3)
1.383(2)
1.389
1.40(2)
1.385
1.391
r(C3-C4)
1.403(2)
1.405
1.39(2)
1.412
1.423
r(C4-C5)
1.405(3)
1.410
1.404(14)
1.407
1.412
r(C3-H1)
1.080(1)
1.086
1.08(2)
1.085
1.098
r(C4-H2)
1.082(1)
1.088
1.084(9)
1.087
1.100
r(C-C) b
1.3914(1)
1.395
r(C-H) b
1.0825(3)
1.087
Benzene
[a] S. G. Kukolich, M. C. McCarthy, P. Thaddeus, J. Phys. Chem A 108 (2004) 2645-2651.
[b] S. G. Kukolich, C. Tanjaroon, M. C. McCarthy, P. Thaddeus, J. Chem. Phys. 119 (2003) 4353-4359.
[c] C. J. Cramer, Nash, J. J. and R. R. Squires, Chem. Phys. Lett. 277 (1997) 311-320.
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Acknowledgements
• Willis Flygare and Terry Balle
•Harvard: Pat Thaddeus, Mike McCarthy
•Arizona: Kristen Keck
•Edingburgh: Martyn Guest, Phillip Camp
•Department of Chemistry, University of Arizona.
• N$F - This material is based upon work supported by the National
Science Foundation under Grant No. CHE-0304969. This support from
the National Science Foundation is gratefully acknowledged
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Other isomers of benzyne
The structural isomers of didehydrobenzene –
ortho-benzyne, meta-benzyne and para-benzyne.
Calculations show Hf(o-benzyne) >Hf(mbenzyne)>Hf(p-benzyne)
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O - BENZYNE
Brown, Godfrey, Rodler, Robertson (1st
microwave, no structure)
Pyrolyzed: pthalic anhydride, or ninhydrin, or
benzocyclobutene-R (1986, 2003)
Lineberger, Squires, et al. (1998)- electron
afinities, singlet triplet splittings & vibrational
frequencies
• PRESENT WORK (2002…)
Discharge 0.5% BENZENE in NEON
HARVARD SPECTROMETER (Sabbatical)
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