Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie...

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WEAK CHWEAK CH……F BRIDGES AND INTERNAL DYNAMICSF BRIDGES AND INTERNAL DYNAMICS

IN THE CHIN THE CH33F-CHFF-CHF33

MOLECULAR COMPLEX MOLECULAR COMPLEX

Walther Caminati, Università di Bologna, ItalyJuan C. Lopez, Jose L. Alonso, Universidad de Valladolid, Spain

Jens-Uwe Grabow, Universität Hannover, Germany

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Hydrogen 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).

E. Kryachko, S. Scheiner, J. Phys. Chem. A 108 (2004) 2527.

S. N. Delanoye, W.A. Herrebout, B.J. Van der Veken, J. Am. Chem. Soc. 124 (2002) 11854.

data are available from X-ray diffraction, theoretical calculations, IR absorption in rare gas solutions, and rotationally resolved spectroscopy.

T. Steiner, Angew. Chem. 114 (2002) 50; Angew. Chem. Int. Ed. 41 (2002) 48.

C. G. Cole, A. C. Legon, Chem. Phys. Lett. 396 (2003) 31.

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•Supersonic Jet ExpansionMolecular ClustersHydrogen BondingConformational

Equilibria •Molecular Dynamics

Large Amplitude MotionsInternal Rotation

FT-MW spectroscopy of species withweak hydrogen bonds (WHB)

Standard ab-initio and DFT calculations: Gaussian or Gamess.

Economy calculations: Distributed polarizability model.

Conformations and potential energy surfaces of molecular adducts.

Effective Hamiltonian fits: Watson, coupled, …

Analysis withobs.-calc. deviations down to a few kHz (< 10-7 cm-1).

Effective potential function fits: flexible model

Inclusion of structural relaxations.

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Bologna supersonic jet FT-MW Spectrometer:

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Coaxial oriented Beam-Resonator Arrangement (COBRA)

Fabry-Perot resonator

resonatortuning

FT

FID

Impulse

polarization pulse:

coherence between

rotating molecular dipoles

oscillating macroscopic

dipole moment:

electromagnetic field at frequencies

of molecular transitions

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Plausible Conformations of CH3F…CHF3

MP2/6-311++G(2df,2p):

E/cm-1 I: 713.8 II: 0.0 III: 29.7 IV: 113.9 V: 119.7

I II III IV V

I + II: minima.Three non-linearweek hydrogen-bonds (WHB)different dipole-dipole

interaction.III + V: saddle points.

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Permutation inversion group theory

CH3 group & CF3 group: C3(1)C3(2) = G9

Cs point group symmetry: E,

Molecular symmetry group: G18

H1

Cl

H3H2

C3 axis

C3 E C3 C3²

E (123) (123)² = (132)A1 1 1 1

E 1 *

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.

C3 group

X1

X2X3

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Tunneling pathways and Tunneling Hamiltonian Matrix

symmetric matrix, 5 eigenvalues:

W1= W(A1)=H11+2HH+2HF+2HA+2HG

W2=W3=W(E1)=H11+2HH-HF-HA-HG

W4=W5=W(E2)=H11-HH+2HF-HA-HG

W6=W7=W(E3)=H11-HH-HF+2HA-HG

W8=W9=W(E4)=H11-HH-HF-HA+2HG

HH: rotation of CH3-groupHF: rotation of CF3-groupHA: anti-geared rotation of CX3-groupsHG: geared rotation of CX3-groups

H11

H11

H11

H11

H11

H11

H11

H11

H11

HH HH

HH

HH

HH

HH

HHHH

HH

HF

HF

HF

HF

HF

HF

HF

HF

HF HA

HA

HA

HA

HA

HA

HA

HA

HA HG

HG

HG

HG

HG

HG

HG

HG

HG

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Energy level splitting diagram for K = 0

HH >> HF > HA ≈ -HG Γ(G18)

J0J

-CH3 -CF3

E

EE

EA

AE

A

AA

E4

E2

E1

A1

Δ'AE

ΔAE

E3

2HH

2HF

2HA 2HG

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Internal Rotation Fine Structure

J,Ka,Kc ← J,Ka,Kc = 31,3←21,2

CH3 top & CF3 top

Only one splitting observed

Effective moment of inertia Iα = 86.0(3) uÅ2 for A1-E1 splitting of CH3F-CHF3

only slightly smaller thanIα = 89.23(2) uÅ2 for isolated CHF3

E1

A1 E1

A1

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CH3F-CHF3 CH3F-13CHF3 13CH3F-CHF3

A/MHz 6451.696(2) 6456(5) 6440(2)

B/MHz 1459.976(6) 1456.23(2) 1430.48(1)

C/MHz 1413.440(6) 1410.10(2) 1386.47(1)

DJ/kHz 2.740 (3) 2.720(7) 2.668(3)

DJK/kHz 53.44(2) 52.2(5) 51.2(2)

DK/kHz 16.3(3) [16.3] [a] [16.3] [a]

dJ/kHz 0.222(2) 0.219(5) 0.204(2)

dK/kHz 1.4(90) [1.4] [a] [1.4] [a]

I / u Å2 86.0(3) 89(3) 86(2)

(a, i) / 51.4(1) 53(2) 50.6(8)

V3 / kJ mol-1 0.840(5) 0.80(3) 0.88(2)

Pbb/uÅ2 44.865(1) [b] 44.82(4) 44.85(2)

CH3F-CHF3 Spectrocopic Constants and CF3-Top Internal Rotation

[a]: Parameter fixed to value of normal species.

[b]: Smaller than sum of values of CH3F and CHF3.

CF3

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Oxirane-Difluoromethane: Planar Moment

Pii = 1/2 (-Iii + Ijj + Ikk) , i,j,k = a,b,c

S. Blanco, J.C. Lopez, A. Lesarri, W. Caminati, J.L. Alonso, ChemPhysChem 5 (2004) 1779.

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CH3-Top Internal Rotation

Pbb of the complex should amount to

Pbb(CHF3) + Pbb(CH3F) = 1.55 uÅ2 + 44.62 uÅ2 = 46.17 uÅ2.

Experimental Pbb of the complex isPbb(CHF3

…CH3F) = 44.69 uÅ2, i.e. 1.48 uÅ2 smaller.

Planar moment of inertia Pbb = (h/16π2)(-1/B + 1/A + 1/C)

is related to V3 barrier of internal rotor by:

A00 = Ar + W00(2) F ρa

2

B00 = Br

C00 = Cr+ W00(2) F ρc

2

Experimental Pbb is reproduced for

V3 (CH3) = 0.36 kJ/mol (= 30 cm-1).

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Barriers to Internal Rotation:CH3 and CF3 Tops

V3 (CH3) = 0.36 kJ/mol

V’3 (CF3) = 0.840(5) kJ/mol

MP2/6-311++G(2df,2p): EXPERIMENTAL:

from planar moments Pbb

from A1-E1 splittings

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Internal rotor CF3 CH3

I / u Å2 85.0 3.20

V3 / kJ mol-1 0.840 0.36

s = 4V3/9F 67.92 2.5

AE[a] / MHz 2.6·10-1 1.2·105

Nlevels[b] 12 2

CF3 and CH3 Internal Rotors:

Energy Spacing

Barrier & Inertia

Ratio 106

[a]: Energy spacing between A1 and E1 or E2 sublevels.

[b]: Number of torsional levels below the V3 barrier.

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CF3 and CH3 LAM Potential Surface

Weak CH···F Bridges and Internal Dynamics inthe CH3F·CHF3 Molecular Complex**

Walther Caminati,* Juan C. Lòpez, José L. Alonso, and Jens-Uwe Grabow

Angew. Chem. Int. Ed. 2005, 44, 3840-3844

Molecular Complexes VIP

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CH3F…CHF3 Complex:Force Constant and Dissociation Energy

Stabilized by three weak CHF hydrogen bonds (WHB)and electrostatic dipole-dipole interaction.

ks = 5.2 Nm-1

ED = 5.3 kJ·mol-1 1.8 kJ·mol-1/[CHF] (<< 25kJ·mol-1)

DJ = DJ(eff) – [-1/2 (ρb4 + ρc

4) W00(4) F] (small contribution)

ks = 16π4 (μ RCM)2 [4B4 + 4C4 - (B-C)2 (B+C)2] / (h DJ)ED(Lennard-Jones) = 1/72 ks RCM

2

V’3 (CF3) = 0.84 kJ·mol-1

V3 (CH3) = 0.36 kJ·mol-1

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Structural Parameters

r0 rs MP2/6-311 ++G(2df,2p)

r(FCH3F…HCHF3)/pm 242.7(10)[a] 240.5

α/° 124.1(3) [a] 122.3

β/° 115.5(3) [a] 109.9 r(FCHF3…HCH3F)/pm 305.2[b] 284.2 r(CCH3F…CCHF3)/pm 364.5[b] 360(2) [c] 352.2

[a] fitted parameter

[b] derived parameter[c] from rs coordinates

CCHF3: |a| = 84(6) pm

|b| = 0*

|c| = 43(4) pm

CCH3F: |a| = 261.9(7) pm

|b| = 0*

|c| = 57(3) pm

*set to zero because imaginary

rα

β

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AcknowledgementAcknowledgement

Deutsche Forschungsgemeinschaft (DFG)

Land Niedersachsen

Deutscher Akademischer

Austauschdienst (DAAD)

Directión General de Investigación –

Ministerio de Ciencia y Technología the

Junta de Castilla y León

Minister of Education, Spain

Università di Bologna

Minister of Education, Italy

Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie...

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Transcript of Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A.ppt Zentrum für Festkörperchemie...