Rotational spectrum and structure of 2-chlorothiophene and its complex with argon

doi:10.1016/j.saa.2019.03.102

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Volume 218, 5 July 2019, Pages 136-141

https://doi.org/10.1016/j.saa.2019.03.102 Get rights and content

Highlights

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2-chlorothiophene monomer and its van der Waals complex were investigated by microwave spectroscopy.
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The nature of non-bonding interaction within the complex was revealed by NCI, SAPT and NBO analysis.

Abstract

2-chlorothiophene and its van der Waals complex with argon were studied by supersonic-jet Fourier transform microwave spectroscopy. Rotational measurements of parent and the mono-substituted ³⁷Cl, ³⁴S and ¹³C isotopologues of the monomer allowed its precisely structural determination. Rotational spectra of ³⁵Cl and ³⁷Cl isotopologues were observed and assigned for the van der Waals complex of 2-chlorothiophene with Ar. Ab initio calculations carried out at the MP2/6-311++G(d,p) level of theory complement the experimental studies. Spectroscopic and theoretical results support a conformation in which the Ar atom locates above the plane of aromatic ring and toward the substituted carbon atom. The distance between the centers of mass of 2-chlorothiophene and argon is 3.589 Å. The Non-Covalent Interaction analysis and Symmetry-Adapted Perturbation theory were performed to reveal the nature of the non-covalent interaction within the complex.

Graphical abstract

Introduction

Van der Waals interaction between rare gases and the partner molecules ranks the weakest among the non-covalent interactions, with interaction energy within a few kJ·mol⁻¹, which therefore is more susceptible to being perturbed than other kinds of non-covalent interactions. The study of weakly bound complexes of rare gases promises to reveal the details and the origin of intermolecular forces. Gas-phase high resolution spectroscopic methods, especially the Fourier transform microwave (FTMW) spectroscopy and its combination with supersonic expansion [[1], [2], [3]], are ideal for studying this kind of weakly bound complexes.

A large number of van der Waals bound complexes have been investigated by rotationally resolved spectroscopy [4,5], many of which were dedicated to the complexes of rare gases with aromatic molecules. A prototype investigation is the structural determination of the benzene-Ar complex [6]. Subsequently, Ar complexes with hetero-aromatic molecules like pyrrole [7], thiophene [8,9], furan [10] and pyridine [11] have also been investigated by rotational spectroscopy. All the complexes have configuration with the Ar atom locating above the plane of the aromatic ring. The distance between the centers of mass (CM) of the monomers and Ar atom is more than 3.5 Å, which is much longer than other intermolecular non-covalent interaction distances, such as the OH⋯π linkage (2.48 Å) in the ethylene-water complex [12] and that of CH⋯π (2.37 Å) in the benzene-trifluoromethane complex [13]. In addition, benzene forms T-shape dimer showing dramatic internal dynamics effect in its rotational spectrum. [14,15]

Rotational spectroscopic investigations have been extended to the derivatives of benzene, because the exact position of Ar atom reflects the distribution of π-electrons in the aromatic ring. Comparing with benzene-Ar complex [6], the Ar atom moves slightly closer to the ring and shifts from a position above the center of the aromatic ring toward the substituted carbon atom in fluorobenzene-Ar [16], reflecting the change of the distribution of π-electrons in the aromatic ring caused by fluorination. For the chlorobenzene-Ar complex [17], the perpendicular distance between Ar and the aromatic ring is 3.540 Å, which is shortened comparing to that of benzene-Ar complex (3.586 Å) and fluorobenzene-Ar complex (3.572 Å).

It is therefore worthwhile to investigate whether the perturbation of the structure due to halogenation will be observed in thiophene and its derivatives. In this paper, 2-chlorothiophene and its complex with Ar were taken as the prototype and were compared with that of the thiophene-Ar complex. The thiophene-Ar complex has been investigated previously [8,9]. The rotational spectra of the parent and ³⁷Cl species of 2-chlorothiophene monomer have been also measured [18]. Before investigating the 1:1 complex of 2-chlorothiophene with Ar, the rotational spectra of the 2-chlorothiophene monomer were remeasured in a supersonic jet cooled molecular beam by using a high resolution FTMW spectrometer. The measurements were also extended to the ³⁴S and ¹³C isotopologues in natural abundance.

Section snippets

Experimental methods

A coaxially oriented beam-resonator arrangement (COBRA)-type [2] pulsed supersonic jet FTMW spectrometer [1], covering frequency range of 2–20 GHz, [19] was used to collect the rotational spectra of 2-chlorothiophene monomer and its argon van der Waals complex. A commercial sample of 2-chlorothiophene was used without further purification. The spectra of the mono-substituted ³⁷Cl, ³⁴S and ¹³C isotopologues of the monomer and the ³⁷Cl isotopologues of the complex were measured in their natural

2-chlorothiophene monomer

Guided by the rotational constants and the quadrupole coupling constants reported by Mjöberg et al. [18], rotational spectra for the parent and the ³⁷Cl species of the 2-chlorothiophene monomer were remeasured in the range of 2–20 GHz. The frequency accuracy of the measurement is improved to 5 kHz. The resolution of the spectrum is also improved. Fig. 2 (a) shows the ³⁵Cl quadrupole coupling hyperfine structure of the 4₀₄ ← 3₀₃ transition. In total, 110 a-type and 57 b-type transitions were

Conclusions

We reported the rotational spectroscopic study of 2-chlorothiophene and its van der Waals complex with argon. The molecular structure of the monomer was precisely determined. Experimental results prove that argon locates above the plane of aromatic ring and toward the substituted carbon atom in the 2-chlorothiophene-Ar complex. The distance between Ar and the center of mass of 2-chlorothiophene is determined to be 3.589 Å, 0.035 Å shorter than that of the thiophene-Ar complex. This structural

Acknowledgments

This work was supported by the Foundation of 100 Young Chongqing University, the Fundamental Research Funds for the Central Universities (Nos. 106112017CDJQJ228807, 10611CDJXZ238826 and 2018CDQYHG0009), National Natural Science Foundation of China (Grant 21703021), Fundamental and Frontier Research Fund of Chongqing (Nos. cstc2017jcyjAX0068 and cstc2018jcyjAX0050) and Venture & Innovation Support Program for Chongqing Overseas Returns (No. cx2018064).

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View full text

Rotational spectrum and structure of 2-chlorothiophene and its complex with argon

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental methods

2-chlorothiophene monomer

Conclusions

Acknowledgments

Chem. Phys.

J. Mol. Struct.

J. Mol. Struct.

J. Mol. Spectrosc.

Fabry–Perot cavity pulsed Fourier transform microwave spectrometer with a pulsed nozzle particle source

Rev. Sci. Instrum.

A multioctave coaxially oriented beam-resonator arrangement Fourier-transform microwave spectrometer

Rev. Sci. Instrum.

Microwave spectroscopy of ternary and quaternary van der Waals clusters

Int. Rev. Phys. Chem.

Bibliography of rotational spectra of weakly bound complexes

Intermolecular dynamics of benzene–rare gas complexes as derived from microwave spectra

J. Chem. Phys.

Pyrrole-Argon: microwave spectrum, structure, dipolemoment, and 14N quadrupole coupling constants

J. Phys. Chem.

The microwave spectrum of the thiophene-Argon van der Waals complex

Z. Naturforsch.

Rotational spectra of pyridine-(Argon)n, n = 1,2, complexes and their vibrationally averaged structures

J. Phys. Chem.

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J. Chem. Phys.

Pyrrole-Argon: microwave spectrum, structure, dipolemoment, and ¹⁴N quadrupole coupling constants

Rotational spectra of pyridine-(Argon)_n, n = 1,2, complexes and their vibrationally averaged structures