Nicholas R. Walker, David Hird, Anthony C. Legon 1 68 th International Symposium on Molecular Spectroscopy, Ohio State University, Broadband Rotational Spectrum and Molecular Geometry of N 2  ICF 3 Engineering and Physical Sciences Research Council

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 ICF 3. CF 3 I 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, (2009)

C O I I H2OH2O H2SH2S I B  ICF 3 Complexes C2H4C2H4 I H3NH3N 1 S.L. Stephens et al., Phys. Chem. Chem. Phys (2011) 2 S.L. Stephens et al., J. Chem. Phys (2011)

Power divider SPST switch Mixer Low noise amplifier Pin diode limiter Adjustable attenuator 300 W Power amplifier AWG ( GHz) Oscilloscope (0-12 GHz) 10 MHz reference frequency PDRO (19.00 GHz) GHz GHz 12.2 GHz Low-pass band filter CP-FTMW Spectrometer

Frequency / MHz 2% 14 N 2, 1% ICF 3, 2 bar argon, averages Frequency / MHz Frequency / MHz J   J = 9  10 J   J = 8  9 J   J = 12  13 Exp. Sim. Exp. Sim. 14 N 2  ICF 3

Frequency / MHz Frequency / MHz Frequency / MHz J   J = 9  10 J   J = 8  9 Sim. Exp. Sim. J   J = 12  13 Sim. Exp. 2% 15 N 2, 1% ICF 3, 2 bar argon, averages. 15 N 2  ICF 3

14 N 2  ICF 3 15 N 2  ICF 3 B 0 / MHz (21) (68) D J / kHz (60) (20) D JK / kHz 6.838(22)6.2152(52)  aa (I) /MHz  (53)  (11) N  / kHz Spectroscopic Fitting of N 2  ICF 3 Data

Molecular Geometry of N 2  ICF 3 Molecule is a C 3v symmetric top. Assuming that a halogen bond forms between I and N 2, the geometry is as shown above. A geometry in which N 2 attaches to the reverse side of CF 3 I cannot be excluded from possibility. Length of the halogen bond determined to be (3) Å while neglecting angular oscillations of the two sub-units. If angular oscillations of the ICF 3 sub-unit are of similar magnitude to those in OC  ICF 3 (4.0  0.5  ), the halogen bond length is as much as Å longer. 1 The halogen bond length will be relatively insensitive 1 to angular oscillations in the N 2 sub-unit. * From arguments presented in S.L. Stephens and co-workers, J. Chem. Phys. 135, (2011)

k  (B  ICl) k  (B  ICF 3 ) Kr N2N2 CO H2SH2S H2OH2O NH 3 Comparison with B  ICl Data consistent with trend established for other B  ICF 3 complexes. Complexes formed between B and ICl are more strongly bound than those formed between B and ICF 3. 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) Financial Support Engineering and Physical Sciences Research Council Bristol In transit Newcastle