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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