Transcript N2_ICF3.pptx

1
Engineering and
Physical Sciences
Research Council
Broadband Rotational Spectrum and
Molecular Geometry of N2ICF3
Nicholas R. Walker, David Hird, Anthony C. Legon
68th International Symposium on Molecular
Spectroscopy, Ohio State University, 2013.
Introduction
• Perfluoroiodoalkanes are a fundamental building block in crystal
engineering that exploits halogen bonding.1 Key intermediates in
synthesis of fluoropolymers such as fluorinated elastomers.
• Provides an opportunity to quantify differences between halogen
bonds to the iodine atoms of ICl and ICF3.
• CF3I and complexes containing this molecule are excellent targets
for study by broadband rotational spectroscopy because of
extensive nuclear quadrupole coupling and relatively intense
transitions.
1.
P. Metrangolo, Y. Carcenac, M. Lahtinen, T. Pilati, K. Rissanen, A. Vij and G. Resnati,
Science, 323 1461 (2009)
BICF3 Complexes
I
C
O
H3N
I
H2O
I
H2S
C2H4
I
1 S.L.
Stephens et al., Phys. Chem.
Chem. Phys. 13 20736 (2011)
2 S.L. Stephens et al., J. Chem. Phys.
135 224309 (2011)
CP-FTMW Spectrometer
Pin diode limiter
300 W Power
amplifier
SPST switch
Adjustable
attenuator
Low noise amplifier
7.0 - 18.5 GHz
7.0 - 18.5 GHz
Power divider
Mixer
12.2 GHz Low-pass band filter
AWG (0.5-12 GHz)
PDRO (19.00 GHz)
10 MHz reference frequency
Mixer
Oscilloscope (0-12 GHz)
2% 14N2, 1% ICF3, 2 bar argon, 77786 averages.
J  J = 8  9
Exp.
14N
2ICF3
J  J = 9  10
Exp.
Sim.
Sim.
9750 9800 9850 9900 9950
Frequency / MHz
10900 11000 11100
Frequency / MHz
J  J = 12  13
Exp.
Sim.
14220
14230
Frequency / MHz
14240
2% 15N2, 1% ICF3, 2 bar argon, 77786 averages.
J  J = 8  9
15N
2ICF3
J  J = 9  10
Exp.
Exp.
Sim.
Sim.
9420 9440 9460 9480 9500
Frequency / MHz
10500 10520 10540
Frequency / MHz
J  J = 12  13
Exp.
Sim.
13670
13680
13690
13700
Frequency / MHz
13710
Spectroscopic Fitting of N2ICF3 Data
14N ICF
2
3
15N ICF
2
3
B0 / MHz
DJ / kHz
DJK / kHz
547.36978(21)
526.580437(68)
0.2991(60)
0.21536(20)
6.838(22)
6.2152(52)
aa(I) /MHz
2135.27(53)
2135.55(11)
N
147
186
 / kHz
17.7
6.3
Molecular Geometry of N2ICF3
• Molecule is a C3v symmetric top. Assuming that a halogen bond forms
between I and N2, the geometry is as shown above. A geometry in which N2
attaches to the reverse side of CF3I cannot be excluded from possibility.
• Length of the halogen bond determined to be 3.4367(3) Å while neglecting
angular oscillations of the two sub-units. If angular oscillations of the ICF3
sub-unit are of similar magnitude to those in OCICF3 (4.0  0.5), the
halogen bond length is as much as 0.006 Å longer.1 The halogen bond length
will be relatively insensitive1 to angular oscillations in the N2 sub-unit.
* From arguments presented in S.L. Stephens and co-workers, J. Chem. Phys.
135, 224309 (2011)
Comparison with BICl
NH3
H2S
k(BICl)
H2O
N2
CO
Kr
k(BICF3)
• Data consistent with trend established for other BICF3 complexes.
• Complexes formed between B and ICl are more strongly bound than those
formed between B and ICF3. Both series provide evidence for formation of
halogen bonds.
• Next step will be to determine aa(N) values using the Balle-Flygare FTMW
spectrometer.
Acknowledgements
David Hird (Newcastle)
Susanna Stephens (Bristol)
Anthony C. Legon (Bristol)
Bristol
In transit
Financial Support
Engineering and Physical
Sciences Research Council
Newcastle