chirped-pulse fourier-transform microwave spectroscopy of the prototypical c-h…π interaction: the...
TRANSCRIPT
CHIRPED-PULSE FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY OF THE
PROTOTYPICAL C-H…π INTERACTION: THE BENZENE…ACETYLENE WEAKLY BOUND DIMER
Nathan W. Ulrich,a Nathan A. Seifert,b Rachel E. Dorris,a Ashley M. Anderton,a Rebecca A. Peebles,a
Brooks H. Pate,b Sean A. Peeblesa
a Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 61920
b University of Virginia, Department of Chemistry and Biochemistry, McCormick Rd., PO Box 400319, Charlottesville, VA 22904
Introduction• CH…p (aromatic) interactions– First suggested by Tamres (1952) 1
• HCCH pKa ~ 25– CH4 ~ 48, HCF3 ~ 25.5, HF ~ 3.17
• Few experimental results– Resonance enhanced
multiphoton ionization 2
– Co-crystal 3
2
1 M. Tamres, J. Am. Chem. Soc. 74 (1952) 3375. 2 E. Carrasquillo M., T. S. Zwier, D. H. Levy, J. Chem. Phys. 83 (1985) 4990.3 R. Boese, T. Clark, A. Gavezzotti, Helv. Chim. Acta, 86 (2003) 1085.
2.447 Å at 123 K 2.462 Å at 201 K
CC
3
Previous Work
FBZ…HCl:M.E. Sanz,et al., J. Chem. Phys. 118 (2003) 9278. (BZ)2: M. Schnell, et al., Angew. Chem. Int. Ed., 52 (2013) 1. FBZ…HCCH: N. W. Ulrich, et al., Phys. Chem. Chem. Phys. 15 (2013) 18148. BZ…CF3H: J. C. López, et al., Angew. Chem. Int. Ed. Eng. 45 (2006) 290.
FC6H5…HCl
(C6H6)2
FC6H5…HCCH
C6H6…HCF3
4
Ab Initio Calculations• MP2/6-311++G(2d,2p)• Fluorobenzene-HCCH– ~0.3 D induced dipole observed– Ab initio dipole components in
good agreement with experiment• Benzene-HCCH– C6v, ~0.5 D dipole
Gaussian 09, Revision C.01, M. J. Frisch, et al., Gaussian, Inc., Wallingford CT, 2010.
2.37 Å
2.38 Å
5
Experimental• 0.1% benzene, 0.2% HCCH in Ne, ~1.7 atm– 5 nozzles @ 3.3 Hz, 8 FIDs/gas pulse, 2 ms chirp– Average of 520,000 FIDs– 13C12C5H6 in natural abundance
• Second broadband scan using C6H5D– 400,000 total FIDs, ~3.0 atm
• H13C12CH and H12C13CH on cavity FTMW– 0.5% benzene, 0.5% H13C12CH in He/Ne, ~2.8 atm– 1 nozzle @ 10 Hz, 1 FID/gas pulse
UVa CP-FTMW, Spring 2013
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Spectroscopic Parameters
Ab Initio C6H6 HCCH⋯C6H6 H⋯ 13C12CH
(near BZ)
C6H6 H⋯ 12C13CH
(away from BZ)13C12C5H6 HCCH⋯ C6H5D HCCH⋯
A / MHz 2846 – – – 2837(13) 2764.1(7)
B / MHz 1199 1148.89656(25) 1132.7251(4) 1114.2052(3) 1146.1883(4) 1146.2664(3)
C / MHz 1199 – – – 1141.1364(4) 1130.4918(3)
DJ / kHz – 1.207(3) 1.200(7) 1.151(6) 1.194(5) 1.179(3)
DJK / kHz – 19.977(11) 19.36(4) 19.36(3) 19.81(4) 19.347(12)
RMS / kHz – 2.2 1.8 1.4 3.7 6.0
N – 22 13 15 21 25
7
r0 (Rcm) r0 (Rcm, θ) r0 (Rcm, ϕ) r0 (Rcm, θ, ϕ) rs Ab Initio
Rcm / Å 4.1546(1) 4.1560(8) 4.1547(1) 4.1554(5) 4.1320(15) 4.0387
θ / ° – 7.4(2.2) – 5.6(1.9) –
ϕ / ° – – 1.0(4) 0.8(2) –
RCH π⋯ / Å 2.4921(1) 2.5073(14) 2.4922(1) 2.5008(89) 2.4717(7) 2.3694
s / u Å2 0.038 0.025 0.017 0.015 –
Structure
RCC = 1.4043(12) Å
RCH = 1.0853(12) Å
RCC Lit.2 = 1.3969 Å
RCH Lit.2 = 1.0815 Å
q
f
r0: 2.4921(1) Års: 2.4717(7) Åre: 2.3694 Å
Rcm
RH…p
r0 (Rcm) r0 (Rcm, θ) r0 (Rcm, ϕ) r0 (Rcm, θ, ϕ) rs Ab Initio
Rcm / Å 4.1546(1) 4.1560(8) 4.1547(1) 4.1554(5) 4.1320(15) 4.0387
θ / ° – 7.4(2.2) – 5.6(1.9) –
ϕ / ° – – 1.0(4) 0.8(2) –
RCH π⋯ / Å 2.4921(1) 2.5073(14) 2.4922(1) 2.5008(89) 2.4717(7) 2.3694
s / u Å2 0.038 0.025 0.017 0.015 –
RCC = 1.1986(7) Å
Lit.1 = 1.203 Å
1 M. D. Harmony, et al., J. Phys. Chem. Ref. Data 8 (1979) 619.2 J. Pliva, et al., J. Mol. Spectrosc., 140 (1990) 214.
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Comparison…Complex ks / N m–1 EB / kJ mol–1 H…p distance / Å
BZ…HF 7.3 6.0 2.25(2)
BZ…HCl 8.0 8.6 2.35(2)
BZ…HBr 7.65 9.1 2.36(2)
BZ…HCF3 6.8 8.4 2.366(2)
BZ…HCN 6.6 8.9 2.38(2)
FBZ…HCl 3.9 4.4 2.456(16)
FBZ…HCCH 2.8 4.1 2.492(47)
BZ…HCCH 4.9(5) 7.1(7) 2.4921(1)
BZ…BZ 0.09 0.19 2.48(2)
BZ…HCCH co-crystal: 2.447 Å at 127 K
10
BZ-HCN BZ-HF BZ-HCl BZ-HBr BZ-HCCH FBZ-HCl FBZ-HCCH0
5
10
15
20
25Binding Energies for XH…p Dimers of
Benzene and Fluorobenzene
CCSD(T)/CBS+BSSE
Pseudodiatomic
Binding Energy Calculations
ωB97XD/aug-cc-pvdz
M062X/aug-cc-pvdz
11
Excited States• Three sets of transitions• Each has a different pattern• All lower than parent• Scale and have similar rotational constant to
parent• Could be intermolecular vibrational modes
J = 4 3
12Frequencies: M. Böning, et al., ChemPhysChem 14 (2013) 837.
x1
n 132 cm-1
x2
n 94 cm-1
x2
n 62 cm-1
Intermolecular Vibrational Modes?J = 5 4
13
Summary, Conclusions, What’s Next? • Trimer(s)? – still unassigned lines with some
interesting patterns…• Need to understand excited states• A reliable frequency calculation would be nice
Trimers: A. Fujii, et al., J. Phys. Chem. A 108 (2004) 2652.
14
Acknowledgements• RUI grant CHE-1214070 (EIU) and MRI-R2
grant CHE-0960074 (UVa) • Pate lab– Brooks Pate– Nate Seifert
• EIU Students – Anu Akmeemana– Cori Christenholz– Lena Elmuti
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Complex
BZ…HF
BZ…HCl
BZ…HBr
BZ…HCF3
BZ…HCN
FBZ…HCl
FBZ…HCCH
BZ…HCCH
BZ…BZ
[BZ…HF] F.A. Baiocchi, et al, J. Phys. Chem., 87, (1983) 2079.
[BZ…HCl] W.G. Read, et al, J. Chem. Phys., 78, (1983) 3501.
[BZ…HBr] S.A. Cooke, et al, Chem. Phys. Lett., 272, (1997) 61.
[BZ…HCF3] J.C. Lopez, et al, Angew. Chem., Int. Ed., 45, (2006) 290.
[BZ…HCN] H. S. Gutowsky, et al, J. Chem. Phys., 103, (1995) 3917.
[FBZ…HCl] M.E. Sanz, et al, J. Chem. Phys., 118, (2003) 9278.
[FBZ…HCCH] N. W. Ulrich, et al, Phys. Chem. Chem. Phys., 15, (2013) 18148.
[BZ…HCCH] N. W. Ulrich, et al, Phys. Chem. Chem. Phys., 16, (2014) 8886.
[BZ…BZ] E. Arunan, et al, J. Chem. Phys., 98, (199), 4294; M. Schnell, et al,
Angew. Chem. Int. Ed., 52, (2013), 5180.
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DFT Calculation for XH…p Interactions• Usual method is MP2/6-311++G(2d,2p)– Need a faster but equally accurate computational
approach
• G09 incorporates new DFT functionals designed for dispersion
2.38 Å
?
?2.37 Å
19
JK' ← JK" |M| Number of
electric fields
30 ← 201 6
2 3
31 ← 210 6
40 ← 303 4
RMS: 5.8 kHz
μ: 0.438(11) D
Estimates of the H π distance range from 2.20 to 2.61 Å,35, 36 with high level ⋯CCSD(T)/aug-cc-pVTZ calculations predicting a distance of ~2.50 Å
M06-2X/6-311+G(d,p) calculation giving an H π distance of 2.393 Å and a binding ⋯energy of 12.2 kJ mol–1.39