Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien HALOGEN BOND AND INTERNAL MOTIONS: THE LOW-BARRIER CASE OF CF 3 Cl-DIMETHYLETHER. LUCA EVANGELISTI, GANG FENG, QIAN GOU AND WALTHER CAMINATI, Università di Bologna, Italy JENS-UWE GRABOW, Universität Hannover, Germany

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Non-covalent Bond Interactions A) Normal Hydrogen Bond (Strong, 25 kJ/mol) B) Improper Hydrogen Bond (Weak, << 25 kJ/mol) C) Anti Hydrogen Bond (Weak, << 25 kJ/mol) The weak hydrogen bond in structural chemistry and biology, IUCr Monographs on crystallography, Vol. IX (G.R. Desiraju, T. Steiner eds.), Oxford University Press (2001). S. N. Delanoye, W.A. Herrebout, B.J. Van der Veken, J. Am. Chem. Soc. 124 ( 2002 ) data are available from X-ray diffraction, theoretical calculations, IR absorption in rare gas solutions, and rotationally resolved spectroscopy. C. G. Cole, A. C. Legon, Chem. Phys. Lett. 396 (2003) 31. Halogen Bond D. Hauchecorne, B. J. van der Veken, A. Moiana, W. Herrebout, Chem. Phys. 374 (2010) 30; D. Hauchecorne, R. Szostak, W. A. Herrebout, B. J. van der Veken. ChemPhysChem 10 (2009) A. C. Legon, Angew. Chem. Int. Ed. 38 (1999) 2686; A. C. Legon, Phys. Chem. Chem. Phys. 12 (2010) 7736.

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Supersonic Jet Expansion Molecular Clusters non-covalent Bonding Conformational Equilibria Molecular Dynamics Large Amplitude Motions Internal Rotation FT-MW spectroscopy of species with non-convalent halogen bonds (HaB) Standard ab-initio and DFT calculations: Gaussian or others. Economy calculations: Distributed polarizability model. Conformations and potential energy surfaces of molecular adducts. Effective Hamiltonian fits: Watson, coupled, … Analysis with obs.-calc. deviations down to a few kHz (< cm -1 ). Effective potential function fits: flexible model Inclusion of structural relaxations. The HaB is competitive and sometimes preferred to the HB. The HaB is often more linear than the HB, with B···X-Y angles ~180°.

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Bologna supersonic jet FT-MW Spectrometer I:

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Plausible Conformations of Dimethylether…Cl-CF 3 MP2/ G(d,p): Four configurations of CF 3 Cl- DME have been found to be stable within 1000 cm -1.

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien PI group theory Dimethylether…Cl-CF 3 2 x CH 3 group & CF 3 group: C 3 (1) C 3 (1) C 3 (2) = G 27 C s point group symmetry:E, Molecular symmetry group: G 54 (all internal rotations feasible) C 3 axis C3C3 EC3C3 C3²C3² E(123)(123)² = (132) A1A1 111 E1 * 1 * H. C. Longuet-Higgins, Mol. Phys. 6 (1963), 445. J. T. Hougen, J. Chem. Phys. 37 (1962), 1433; J. Chem. Phys. 39 (1963), 358. C 3 group X1X1 X2X2 X3X3 Γ( G 54 ): A 1, E 1, E 2, E 3, E 4, E 5, G 1, G 2, G 3, G 4 But no internal rotation splitting observed!

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Another case: PI group theory CH 3 -F…H-CF 3 CH 3 group & CF 3 group:C 3 (1) C 3 (2) = G 9 C s point group symmetry:E, Molecular symmetry group: G 18 C 3 axis C3C3 EC3C3 C3²C3² E(123)(123)² = (132) A1A1 111 E1 * 1 * C 3 group X1X1 X2X2 X3X3 Γ( G 18 ): A 1, E 1, E 2, E 3, E 4 Only one internal rotation splitting (A 1, E 1 ) observed!

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien CF 3 -Top Internal Rotation Fine Structure J,K a,K c J,K a,K c = 3 1,32 1,2 CH 3 top & CF 3 top Only one splitting observed Effective moment of inertia I α = 86.0(3) uÅ 2 for A 1 -E 1 splitting of CH 3 F-CHF 3 only slightly smaller than I α = 89.23(2) uÅ 2 for isolated CHF 3 E1E1 A1A1 E1E1 A1A1

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Rigid Oxirane-Difluoromethane: Addivity of Planar Moments P ii = 1/2 (-I ii + I jj + I kk ), i,j,k = a,b,c S. Blanco, J.C. Lopez, A. Lesarri, W. Caminati, J.L. Alonso, ChemPhysChem 5 (2004) 1779.

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien CH 3 -Top Internal Rotation Inertia Defect P bb of the complex should amount to P bb (CHF 3 ) + P bb (CH 3 F) = uÅ uÅ 2 = uÅ 2. Experimental P bb of the complex is P bb (CHF 3 … CH 3 F) = uÅ 2, i.e uÅ 2 smaller. Planar moment of inertia P bb = (h/16π 2 )(-1/B + 1/A + 1/C) is related to V 3 barrier of internal rotor by: A 00 = A r + W 00 (2) F ρ a 2 B 00 = B r C 00 = C r + W 00 (2) F ρ c 2 Experimental P bb is reproduced for V 3 (CH 3 ) = 0.36 kJ/mol (= 30 cm -1 ).

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Barriers to Internal Rotation: CH 3 and CF 3 Tops V 3 (CH 3 ) = 0.36 kJ/mol V 3 (CF 3 ) = 0.840(5) kJ/mol MP2/ G(2df,2p): EXPERIMENTAL: from planar moments P bb from A 1 -E 1 splittings

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien CF 3 and CH 3 Internal Rotors: Energy Spacing Barrier & Inertia Ratio 10 6 [*]: Energy spacing between A 1 and E 1 or E 2 sublevels. Weak CH···F Bridges and Internal Dynamics in the CH 3 F·CHF 3 Molecular Complex** Walther Caminati,* Juan C. Lòpez, José L. Alonso, and Jens-Uwe Grabow Angew. Chem. Int. Ed. 2005, 44, Molecular Complexes VIP

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Dimethylether…Cl-CF 3 : MP2/ G(d,p) results for most stable conformers IIIIIIIV A/MHz B/MHz C/MHz μ a /D-1.1,-2.1,-2.3, μ b /D-0.1,0.0, μ c /D χ aa /MHz (χ bb -χ cc )/MHz χ ab /MHz χ ac /MHz χ bc /MHz

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Dimethylether…Cl-CF 3 : Spectrocopic Constants for observed isotopologs 35 Cl 37 Cl A/MHz11738(8)11616(11) B/MHz (9) (1) C/MHz (7) (1) χ aa /MHz (3)-60.0(2) (χ bb -χ cc )/MHz2.46(4)0.7(6) D J /kHz1.146(4)1.077(5) D JK /MHz-1.008(3) (3) d 1 /kHz0.027(1)0.094(7) H J /Hz-0.220(1)-0.39(2) h 1 /Hz-0.080(2)-0.27(3) b /kHz 10.0 NcNc 8061

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Dimethylether…Cl-CF 3 : Planar Moment P bb of the complex should amount to P bb (CHF 3 )+P bb (H 3 COCH 3 )=44.62 uÅ uÅ 2 =89.62 uÅ 2 Experimental P bb of the complex is P bb (CHF 3 … H 3 COCH 3 ) = uÅ 2, i.e uÅ 2 smaller. Planar moment of inertia P bb = (h/16π 2 )(-1/B + 1/A + 1/C) is related to V 3 barrier of internal rotor by: A 00 = A r + W 00 (2) F ρ a 2 = A r + W 00 (2) F ρ a 2 B 00 = B r + W 00 (2) F ρ b 2 = B r C 00 = C r + W 00 (2) F ρ c 2 = C r Experimental P bb is reproduced for V 3 (CF 3 ) = ~0 kJ/mol (VERY SMALL).

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Dimethylether…Cl-CF 3 Complex: Force Constant and Dissociation Energy O ClC halogen bond (HaB) k s = 1.3 Nm -1 E D = 2.7 kJ·mol -1 (similar to weak hydrogen bond (HB) << 25 kJ/mol) D J = D J (eff) – [-1/2 (ρ b 4 + ρ c 4 ) W 00 (4) F] (small contribution) k s = 16π 4 (μ R CM ) 2 [4B 4 + 4C 4 - (B-C) 2 (B+C) 2 ] / (h D J ) E D (Lennard-Jones) = 1/72 k s R CM 2

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Coaxial oriented Beam-Resonator Arrangement (COBRA) Fabry-Perot resonator resonator tuning FT FID Impulse polarization pulse: coherence between rotating molecular dipoles oscillating macroscopic dipole moment: electromagnetic field at frequencies of molecular transitions

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien In-Phase/Quadrature-Phase Modulation Passage-Acquired Coherence Technique (IMPACT) FT-MW polarization chirp: superposition of multiple coherence Between rotating molecular dipoles superposition of oscillating macroscopic dipole moments: electromagnetic field at frequencies of participating molecular transitions (LASER-ablation) source planar reflector parabolic reflectors double-ridge horn chirp t FT FID linewidth < 10kHz Doppler doublets

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie & Neue Materialien Acknowledgement Deutsche Forschungsgemeinschaft (DFG) Land Niedersachsen Università di Bologna Minister of Education, Italy