Intermolecular Interaction in the Formaldehyde–Dimethyl Ether and Formaldehyde–Dimethyl Sulfide Complexes Investigated by Fourier Transform Microwave Spectroscopy and ab Initio Calculations

Abstract

The ground-state rotational spectra of the formaldehyde-dimethyl ether: H 2 CO-DME and formaldehyde-dimethyl sulfide: H 2 CO-DMS complexes have been studied by Fourier transform microwave spectroscopy. The a-type and c-type rotational transitions have been assigned for the normal and deutrated formaldehyde containing species of both the complexes. In the case of the H 2 CO-DME, doublets were observed with the splitting of 10~300 kHz, whereas no such splittings were observed for the H 2 CO-DMS, D 2 CO-DME, and D 2 CO-DMS. The observed rotational spectra were found consistent with a structure of C s symmetry with DME or DMS bound to H 2 CO by two types of hydrogen bonds: C-H(DME/DMS)---O(H 2 CO) and O(DME)/S(DMS)---H-C(H 2 CO). TheR cm distances between the centers of mass of the component molecules in the H 2 CO-DME and H 2 CO-DMS complexes were determined to be 3.102 and 3.200 Å, respectively, which are shorter than those in most related complexes. The spectral and NBO analyses showed that the H 2 CO-DMS has stronger charge transfer interaction than the H 2 CO-DME does and that the binding energy of the H 2 CO-DMS is larger than that of the H 2 CO-DME.Keywords: van der Waals complexes, rotational spectra, ortho and para hydrogens, hyperfine structure of the deuterium, weak hydrogen bonding, NBO analysis.

Fourier Transform Microwave Spectra of the Nitrogen Molecule–Ethylene Sulfide and Nitrogen Molecule–Dimethyl Sulfide Complexes

“…7 We also reported that in the case of the formaldehyde−DME and formaldehyde−DMS complexes, their CTs are about 5 times larger than their E B 's because formaldehyde is a strong electronic acceptor. 6 The CT of 24.3 kJ/mol of the CO 2 −DME 11 is 2.5 times larger than the E B of 9.7 kJ/mol, and the CTs of 14.1 and 13.5 kJ/mol, respectively, of the CO 2 −EO and CO 2 −ES complexes are 2 times larger than the E B 's of 7.1 kJ/mol for both complexes. 3 As summarized in ref 8, quite a large number of N 2 complexes have been studied.…”

“…In order to study these interactions, we have been investigating complexes in a systematic way by using molecular beam Fourier transform microwave (FTMW) spectroscopy. We tried to select atoms and molecules of high symmetry like C 2 v as components and paid special attention to the differences between the roles of oxygen and sulfur in molecular complexes, as reported in several examples of our previous investigations. − It should be mentioned that recently natural bond orbital (NBO) analysis was applied to explain the hydrogen bond supplemented by other intermolecular interactions such as donor–acceptor and charge-transfer (CT) interactions. , We found that the stabilization energy CT (=Δ E σσ* ) was well correlated with the binding energy E B obtained from experimental results. For example, the CT of dimethyl ether (DME) and/or dimethyl sulfide (DMS) containing complexes is 2.5 times larger than the E B .…”

Dimethyl Sulfide–Dimethyl Ether and Ethylene Oxide–Ethylene Sulfide Complexes Investigated by Fourier Transform Microwave Spectroscopy and Ab Initio Calculation

“…These "internal" rotations may be regarded as an intracomplex motion, following the well-known example of the stretching motion between two component molecules. A significant number of complexes have already been investigated by a few groups including ours, by using Fourier transform microwave (FTMW) spectroscopy, as listed below: CO−EO, 1 CO−ES, 1 CO−DME, 2 CO−DMS, 3 CO 2 −EO, 1 CO 2 −ES, 1 N 2 −EO, 4 H 2 CO−DME, 5 and H 2 CO−DMS. 5 We have also applied a natural bond orbital (NBO) analysis to the complexes to calculate the stabilization energy CT (= ΔE σσ* ), which we found was closely correlated with the binding energies E B .…”

“…A significant number of complexes have already been investigated by a few groups including ours, by using Fourier transform microwave (FTMW) spectroscopy, as listed below: CO−EO, 1 CO−ES, 1 CO−DME, 2 CO−DMS, 3 CO 2 −EO, 1 CO 2 −ES, 1 N 2 −EO, 4 H 2 CO−DME, 5 and H 2 CO−DMS. 5 We have also applied a natural bond orbital (NBO) analysis to the complexes to calculate the stabilization energy CT (= ΔE σσ* ), which we found was closely correlated with the binding energies E B . Legon examined the structures of the EO−HX and ES−HX (X = F, Cl, and Br) complexes and explained the structures and binding energies derived in terms of the hydrogen bond between the lone pair electrons in the O of the EO or in the S of the ES and the H of the HX, which is referred to as the n-pair model.…”

“…In the cases of the H 2 CO−DME and H 2 CO−DMS complexes, the CT is four times larger than the E B because H 2 CO is a strong acceptor. 5 Tatamitani et al reported the microwave spectra of the DME dimer, which consists of weak, improper, C−O···H−C hydrogen bonds and has a structure of C s symmetry with two monomers bound by three weak hydrogen bonds. 7 They reported that the V 3 barrier to "free" DME methyl group internal rotation to be 2.2 kcal/ mol (785.4 cm −1 ), which is smaller than that of the monomer, 2.6 kcal/mol (951.7 cm −1 ).…”