OBSERVATION OF C-H · · · π INTERACTIONS: MICROWAVE SPECTRA AND STRUCTURES OF THE CH 2 FX···HCCH (X=F, Cl) WEAKLY BOUND COMPLEXES Lena F. Elmuti, Daniel A. Obenchain , Don L. Jurkowski, Cori L. Christenholz, Amelia J. Sanders, Rebecca A. Peebles, Sean A. Peebles Department of Chemistry, Eastern Illinois University, 600 Lincoln Avenue, Charleston, IL 61920 Amanda L. Steber, Justin L. Neill, Brooks H. Pate Department of Chemistry, University of Virginia, McCormick Rd., PO Box 400319, Charlottesville, VA 22904
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Lena F. Elmuti, Daniel A. Obenchain, Don L. Jurkowski, Cori L. Christenholz, Amelia J. Sanders, Rebecca A. Peebles, Sean A. Peebles Department of Chemistry,
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OBSERVATION OF C-H · · · π INTERACTIONS: MICROWAVE SPECTRA AND STRUCTURES
OF THE CH2FX···HCCH (X=F, Cl) WEAKLY BOUND
COMPLEXESLena F. Elmuti, Daniel A. Obenchain, Don L. Jurkowski, Cori L. Christenholz,
Amelia J. Sanders, Rebecca A. Peebles, Sean A. Peebles Department of Chemistry, Eastern Illinois University,
600 Lincoln Avenue, Charleston, IL 61920
Amanda L. Steber, Justin L. Neill, Brooks H. PateDepartment of Chemistry, University of Virginia,
McCormick Rd., PO Box 400319, Charlottesville, VA 22904
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Recent work in C-H···π Interactions
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CHClF2···HCCHa
CH2F2···HCCH
CH2ClF···HCCH
aElmuti, L. F.; Peebles, R. A.; Peebles, S. A.; Steber, A. L.; Neill, J. L.; Pate, B. H. J. Phys. Chem. Chem. Phys. 2011, DOI 10.1039/c1cp20684b
Cl
F
3.061(38) Å
2.730(6) Å
Cl
F
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CH2ClF···HCCH ab initio Structures MP2/6-311++G(2d,2p) level
A /MHz 5120
B /MHz 1625
C /MHz 1243
EZPE /cm-1 0
A /MHz 9652
B /MHz 1204
C /MHz 1078
EZPE /cm-1 26
a
b
Chlorine out structureChlorine in structure
b
a
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CH2ClF ··· HCCH Spectrum Measurement
CP-FTMW (University of Virginia)a
7.0-18.0 GHz 350,000 averages 0.75% CH2ClF/ 1.0% HCCH diluted in He, P= 2 atm Fit using AABS package from Kisielb and SPFIT/SPCAT softwarec
Less intense transitions and 13C isotopologues measured on the Balle-Flygare cavity FTMW (Eastern Illinois University)d, e
1.0% CH2ClF/ 1.0% HCCH diluted in He/Ne (17.5%/82.5%) P=2.0-2.5 atm
a Brown, G. G.; Dian, B. C.; Douglass, K. O.; Geyer, S. M.; Shipman, S. T.; Pate, B. H. Rev. Sci. Instrum. 2008, 79, 053103bKisiel, Z.; Pszczolkowski, L.; Medvedev I.R.; Winnewisser, M.; De Lucia, F. C.; Herbst, C. E. J. Mol. Spec. 2005, 233, 231-243cPickett, H. M. J. Mol. Spec. 1991, 148, 371dBalle, T. J.; Flygare, W. H. Rev. Sci. Instrum. 1981, 52, 33e Newby, J. J.; Serafin, M. M.; Peebles, R. A.; Peebles, S. A. Phys. Chem. Chem. Phys. 2005, 7, 487
a number of fitted transitionsb Δνrms=√(∑(νobs-νcalc)2/N)c Blanco, S.; Lesarri. A.; López, J. C.; Alonso, J. L.; Guarnieri, A. J. Mol. Spec. 1995, 174, 397
Pcc (CH2ClF) = 1.6092(1) uÅ2 c
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CH2ClF···HCCH StructureInertial Fit
“Best” a
Ab initio
Chlorine in
R|||…C / Å3.605(4) 3.476
θC–|||…C / °73.9(9) 73.6
θ|||…C–Cl / °91.87(27) 94.3
RCl…H / Å 3.207(22) 3.138
R|||…H / Å 3.236(6) 3.101
θC–H…||| / ° 101.0(1) 101.2
θC–H…Cl / ° 109.0(1.0) 110.1
3.207(22) Å
RH…p = 3.236(6) ÅqC-H…p = 101.0(1)°
91.87(27)°
73.9(9)°
3.605(4) Å
109.0(10)°
85.2(22)°
Cl
F
a average of the structures produced by fitting (Ia, Ib, Ic), (Ia, Ib), (Ia, Ic), and (Ib, Ic) in STRFITQ bΔνrms=√(∑(νobs-νcalc)2/N)
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CH2F2···HCCH Predictions
A /MHz 11211
B /MHz 1703
C /MHz 1493
EZPE /cm-1 0
A /MHz 8121
B /MHz 2067
C /MHz 1838
EZPE /cm-1 64
A /MHz 10588
B /MHz 1498
C /MHz 1323
EZPE /cm-1 165
MP2/6-311++G(2d,2p) level
1 imaginary frequency 1 imaginary frequency
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CH2F2···HCCH Spectrum Measurement
CP-FTMW at Eastern Illinois University1.5% CH2F2/ 1.5% HCCH in 5 bar He/Ne, 1.6 atm backing pressure480 MHz Chirp, 1000 averages7.0 -15.6 GHz
Balle-Flygare FTMW Spectrometer at Eastern Illinois Universitya
aObenchain, D.A.; Elliott, A.A.; Steber, A.L.; Peebles, R.A.; Peebles, S.A. Wurrey, C.J.; Guirgis, G.A. J. Mol. Spec. 2010, 261, 35-40
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CH2F2···HCCH Spectrum
CH2F2···HCCHCH2F2···H2Oa
(CH2F2)3b
(CH2F2)2c
a Caminati,W.; Melendra, S; Rossi, I.; Favero, P. G. J. Am. Chem. Soc. 1999, 121, 10098b Blanco, S.; Melandri, S.; Ottaviani, P. Caminati, W. J. Am. Chem. Soc. 2007, 129 (9), 2700c Blanco, S.; López, J. C.; Lesarri, A.; Alonso, J. L. J. Mol. Struct. 2002, 612, 255
1000 avg scan1.5% CH2F2
1.5% HCCH in 5 bar He/Ne
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From the original 1000 average scan
Only a-types were visible in the original scan
Potential b-type transitions were found in a 2000 average scan with a smaller chirp
Pbb /uÅ2 43.42 41.4554(14) 41.55697(25) 42.0617(16)
Pcc /uÅ2 1.655 1.6774(14) 1.68365(25) 1.6724(16)
Pcc (CH2F2) = 1.6512(1) uÅ2 c
aΔνrms=√(∑(νobs-νcalc)2/N)bnumber of fitted transitionscHirota, E.; Tanaka, T.; Sakakibara, A.; Ohashi, Y.; Morino, Y. J. Mol. Spec. 1970, 34, 222
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CH2F2···HCCH Stark Effects
Transition 105 x (Δν/E2) obs.105 x (Δν/E2)
calc.202←101 |M|= 0 -3.3840 -3.4079
202←101 |M|= 1 2.5522 2.5175
303←202 |M|= 0 -4.4624 -4.4315
303←202 |M|= 1 -3.6005 -3.5966
303←202 |M|= 2 -1.0932 -1.0918
111←000 |M|= 0 6.7099 6.7261
313←212 |M|= 1 -2.9271 -2.9439This Study Ab initioμa /D 1.511(3) 1.68
μb /D 1.2246(19) 1.29
μtotal /D 1.9452(26) 2.12
c
a
b
μtotal (CH2F2) = 1.97(2) Da
a Lide, D. R. Jr. J. Am. Chem. Soc. 1952, 74 (14) 3548
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Inertial Fit“Best”a
Ab initioStructure
R |||···C /Å 3.625(9) 3.51
θC-|||···C/° 70.2(28) 66.5
θ|||···C-F/° 80.0(8) 83.7
RF···H /Å 2.84(6) 2.68
RH···||| /Å 3.363(14) 3.22
Rcm /Å 4.033(1) 3.937
θC-H···|||/° 94.9(3) 96.2
θC-H···F/° 105(3) 111
θC-F···H/° 104.5(13) 99.7
CH2F2···HCCH Structure
3.625(9) Å
RH···||| = 3.363(14) ÅθC-H…||| = 94.9(3)°
70.2(28)°
80.0(8)°
104.5(13)°
105(3)°
2.84(6) Å
a /Å b /Å
Substitution -0.90101(11) -0.33033(2)
Inertial fit (Ia, Ic) -0.9264 -0.3089
Ab initio structure
-0.8788 -0.2956
a average of the structures produced by fitting (Ia, Ib, Ic), (Ia, Ib), (Ia, Ic), and (Ib,Ic) in STRFITQ
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HCCH complex
ks /N m-1 Eb / kJ mol-1
CH2F2 2.85(3) 3.88(6)
CH2ClF 3.46(2) 4.75(4)
CHClF2a 3.7(5)
[3.7(5)]b
4.9(5)[5.0(5)]b
CHBrF2c 1.82(1) 2.46(3)
Force Constants and Binding Energies
aElmuti, L. F.; Peebles, R. A.; Peebles, S. A.; Steber, A. L.; Neill, J. L.; Pate, B. H. Phys. Chem. Chem. Phys. 2011. DOI 10.1039/c1cp20684bbStrucure refit using a refined CHClF2 monomer structure. Vincent, M. A.; Hillier, I. H. Phys. Chem. Chem. Phys. 2011, 13, 4388cObenchain D. A.; Bills, B. J.; Christenholz, C. L.; Peebles, R. A.; Peebles, S. A.; Neill, J. L.; Pate, B. H. Manuscript in preparation
a Strucure refit using a refined CHClF2 monomer structure. Vincent, M. A.; Hillier, I. H. Phys. Chem. Chem. Phys. 2011, 13, 4388
Distributed Multipole AnalysisUp to quadrupole terms considered
GDMA 2.2Anthony Stonea
MIN16Buckingham-Fowler modelb,c
PROSPE websited,e
Electrostatic Interactions
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Lowest Energy Highest Energy
Buckingham-Fowler Model
Ab initioMP2/
6-311++G(2d,2p)
a Stone, A. J. J. Chem Theory Comp. 2005, 1, 1128b Buckingham A. D.; Fowler P. W. J.Chem.Phys. 1983, 79, 6426c Buckingham A. D.; Fowler P. W. Can.J.Chem. 1985, 63, 2018d Kisiel Z.; Fowler, P. W.; Legon A.C. J. Chem. Phys. 1990, 93, 3054e Kisiel Z. MIN16, PROSPE. www.ifpan.edu.pl/~kisiel/prospe.htm
Conclusions Assigned the spectrum of CH2ClF···HCCH (4
isotopologues) and CH2F2···HCCH (3 isotopologues)Structure fits
○ Similar RC-C distance for analog HCCH complexes
Dipole moments of CH2F2···HCCH○ Agree with ab initio to within expected deviation○ No enhancement of the dipole moment from the measured
monomer valueForce constants and binding energies
○ Appears that the chlorine containing halomethanes are more strongly bound to acetylene than the other halomethanes studied thus far
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Conclusions
Intermolecular InteractionsElectrostatic model can be used to predict
possible asymmetric structures ○ Preference of the lowest energy structure cannot be
determined by only an electrostatic model ○ Orient a
Additional studies are still needed to reliably determine the types of intermolecular interactions that are influencing the structures of these complexes
a Stone, A. J.; Dullweber, A.; Engkvist, O.; Fraschini, E.; Hodges, M. P.; Meredith, A. W.; Nutt, D. R.; Popelier, P. L. A.; Wales, D. J. 2002, ‘Orient:
a program for studying interactions between molecules, version 4.5,’ University of Cambridge, Enquiries to A. J. Stone, [email protected]
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Current Projects CH2ClF
Vinyl Fluoride
Vinyl Fluoride
CH2=CH2
CH2=CH2
CO2
CO2
CH2F2
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Support
NSF Research at Undergraduate Institutions CHE-0809387
Professor Kuczkowski for the H13C13CH sample
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Ia, Ib, Ic a Ia, Ib
a Ia, Ic a Ib, Ic
a “Best” b Ab initio
Structure I
R|||…C / Å 3.605(3) 3.608(3) 3.600(3) 3.606(3)3.605(4) 3.476