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CHAKREE TANJAROON, ADAM DALY AND STEPHEN G. KUKOLICH, Department of Chemistry, The University of Arizona, Tucson, Arizona 85721

THE ARGON-CYCLOPENTADIENYL THALLIUM WEAKLY-BOUND COMPLEX, ROTATIONAL SPECTRUM AND STRUCTURE1

1) This material is based on work supported by the National Science Foundation under Grant No. CHE-0721505.

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Calculations were done to see if a bound structure could be obtained for this complex

MP2 and DFT calculations using Gaussian 03

For Tl > aug-cc-pVTZ-PP Other atoms >Dunning’s

aug-cc-pVTZ Tested with Tl - halides

Binding Energy = -6.4 kJ mol-1 = 535 cm-1

Calculated r(Ar-Cp) = 3.46 Å

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Ar-C5H5Tl Prolate symmetric-top rotor with C5V symmetry Argon atom is located on the a-axis of C5H5Tl 26 transitions measured for 205Tl, 15 transitions

for 203Tl Measured intermolecular r(Ar-Cp) =3.56 Å.

(between argon and the cyclopentadienyl ring) DJ = 0.12 kHz, DJK = 0.45 kHz (relatively rigid

complex)

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Example spectrum for the J’K’ → JK = 90 → 80, (A) 91 → 81,

(B) and 92 → 82 (C) transitions. (700 shots)

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Molecular ConstantsMeasured rotational and centrifugal distortion constants obtained for the argon-cyclopentadienyl thallium dimer Parameter Ar-C5H5

205Tl Ar-C5H5203Tl

A /MHz [4365.3727] [4365.3727] B /MHz 372.4479(3) 373.4783(5) C /MHz 372.4479(3) 373.4783(5) DJ /kHz 0.123(2) 0.113(3) DJK /kHz 0.45(2) 0.37(3)

(Fit) /kHz 6.2 5.1 The A rotational constant is fixed to the MP2 calculated value. The standard error is 2

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Intermolecular Potential Pseudo-diatomic - L-J Model

Consider Ar – X as diatomic Lennard - Jones 6-12 Potential VanderWaals stretching freq. = s (2s)2 = 4 B0

3 / DJ = ks / = ks re

2 / 72 Refs:• S. J. Harris, S. E. Novick, W. Klemperer, J. Chem.

Phys 60, 3208 (1974)• M. R. Kennan, E. J. Campbell, T. J. Balle, L. W.

Buxton, T. K Minton. P. D. Soper and W. H. Flygare, J. Chem. Phys. 72, 3070 (1980)

612

4Vrr

r

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Comparison of Ar – X (aromatic) complexes

Parameter Ar-Cp-Tl Ar-benzene1 Ar-furan2

r(Ar-ring)(Ǻ) 3.56 3.59 3.54 B0 (MHz) 372.448 1181.26 1361.5 DJ (kHz) 0.123 3.256 5.27 ks (N/m) 3.83 3.51 3.16 (cm-1) 339 316 277 1. Th. Brupbacher and A. Bauder, Chem. Phys Lett. 173, 435 (1990) 2. S. G. Kukolich, J. Am. Chem. Soc. 105, 2207 (1983)

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Potential energy surface profile for Ar-CpTl evaluated at the MP2/aug-cc-pVTZ-PP (Thallium)/aug-cc-pVTZ(Ar, C, H). The binding energy for the lowest energy structure is 4.6 kJ /mol.

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Results of Calculations: Binding energies (B. E.) evaluated using

the microwave structure, R = 3.56 Å. Expt. B. E. = -4.1 kJ

Dimer Method Basis sets (thallium/C, H, Ar)

B. E.(kJ mol-1)

Ar-C5H5Tl MP4 aug-cc-pVDZ-PP/ aug-cc-pVDZ

-3.9

MP2 (ZPVEcorrected)

aug-cc-pVDZ-PP/ aug-cc-pVDZ

-4.6

MP2 aug-cc-pVDZ-PP/ aug-cc-pVDZ

-5.1

mPW91PW91 (DFT)

aug-cc-pVDZ-PP/ aug-cc-pVDZ

-0.3

B3PW91/B3LYP (DFT)

aug-cc-pVDZ-PP/ aug-cc-pVDZ

UNBOUND

Ar-C6H6 MP2a aug-cc-pVTZ -5.9 CCSD(T) a aug-cc-pVQZ -4.6 Experimentb - -3.8

a H. Koch, B. Fernández, and O. Christiansen, J. Chem. Phys. 108, 2784 (1998 b Th. Brupbacher and A. Bauder, Chem. Phys Lett. 173, 435 (1990)

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Results of geometry optimizations using the MP2 method with

pseudopotential cc-pVDZ-PP basis sets for Thallium. B(exp’t)

=372.4 MHz

Structure C, H, Ar Distance (Å) A / B / C (MHz)a Ar - C5H5Tl aug-cc-

pVDZ Ar-Cp = 3.34 4355 / 397 / 397

Ar - C5H5Tl cc-pVDZ Ar-Cp = 3.60 4365 / 365 / 365 (C5H5Tl)2 (I) 3-21G* Tl-Tl = 3.54 2156 / 1236 / 1236 (C5H5Tl)2 (II) 3-21G* Tl-Tl = 5.51b 1421 / 1144 / 1113

aConverged geometries with real vibration frequencies bTl to CpTl, R=3.05Å

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(C5H5 – Tl)n chain structure from the x-ray measurements1. Exp’t R(Tl-Tl) = 5.5 Å,

Calculated(above) 5.51 Å

1. F. Olbrich, U. Behrens, Zeitschrift fuer Kristallographie - New Crystal Structures (1997), 212(1), 47.

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Plot of the binding energy (cm-1) as a function of r(Ar-Cp) for MP2 and DFT calculations. DFT > UNBOUND

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Acknowledgements

• N$F - This material is based upon work supported by the National Science Foundation under Grant No. CHE-0721505. This support from the National Science Foundation is gratefully acknowledged

•Department of Chemistry, University of Arizona.