The crystal and liquid structures of N,N-dimethylthioformamide and N,N-dimethylformamide showing a stronger hydrogen bonding effect for C–H  · · ·  S than for C–H  · · ·  O †

Abstract

The crystal structures of N,N-dimethylthioformamide and N,N-dimethylformamide were determined at 90 ± 2 K from single crystal X-ray diffraction data. Both compounds comprise planar molecules, a consequence of the π-electron delocalization over the N-C-S and N-C-O entities, respectively. In N,N-dimethylthioformamide, almost linear, 175.4(7)Њ, C-H ؒ ؒ ؒ S cooperative hydrogen bonding between the thioformyl groups connects the molecules in helix-shaped chains with an intermolecular C ؒ ؒ ؒ S distance of 378.10(7) pm. The two crystallographically independent molecules in N,N-dimethylformamide form four-membered centrosymmetric rings held together by C-H ؒ ؒ ؒ O intermolecular interactions, two via the formyl protons, C ؒ ؒ ؒ O 329.41(9) pm, and two involving methyl protons, C ؒ ؒ ؒ O 341.41(9) pm. The structures of both liquids were studied at room temperature by large angle X-ray scattering in transmission mode and for N,N-dimethylthioformamide also in reflection geometry. The structure of liquid N,N-dimethylformamide can, despite the stronger hydrogen bond acceptor properties of the oxygen atom, be described without hydrogen bonding. This apparent anomaly with more significant effect of hydrogen bonding in both crystal and liquid forms of N,N-dimethylthioformamide than N,N-dimethylformamide is discussed using results from theoretical calculations on single molecules. Mulliken population analyses indicate a lower positive charge and thus weaker hydrogen-bond donor properties of the formyl than of the thioformyl hydrogen atom. Raman and infrared spectra of the solids and the liquids are used for discussions of the hydrogen bonding effects.

Vibrational spectroscopic force field studies of dimethyl sulfoxide and hexakis(dimethyl sulfoxide)scandium(iii) iodide, and crystal and solution structure of the hexakis(dimethyl sulfoxide)scandium(iii) ion

“…From the discussion above we conclude that the IR bands at 1070, 1032 and 1012 cm Table 4 can be assigned as m 19 , m 17 , m 6 , m 4 and m 18 modes of different CD 3 deformation and rocking vibrations in the molecular species, 1031.8(104)dp 1028.0(107)dp 1008.7(78)dp…”

“…The 6 ] 3+ complex is due to the complexity of the Sc-O stretching modes, e.g., their interaction with the isotope sensitive deformation modes.…”

“…These are: frequency shifts of the ligand modes, splitting of IR and Raman bands because of the interaction between coordinated OSMe 2 molecules, and the appearance of new bands. The [Sc(OS(CH 3 ) 2 ) 6 ] 3+ complex can be described in the S 6 point group, with the normal vibrations belonging to the symmetry species 11A g + 12A u + 11E g + 12E u , considering the methyl groups as point masses. The "g"-modes are Raman-active whereas the "u"-modes are IR-active.…”

“…2, 3 These dimers are held together by weak C-H · · · O interactions and electrostatic attraction between the negative oxygen and positive sulfur ends of adjacent dipoles in the crystal † Electronic supplementary information (ESI) available: Description of the internal and symmetry coordinates of [Sc(OSMe 2 ) 6 ] 3+ , fundamental vibrations of (CH 3 ) 2 SO and (CD 3 ) 2 SO molecules in 0.6 M CCl 4 solution, intermolecular interactions from dimethyl sulfoxide crystal structure, EXAFS data for [Sc(OSMe 2 ) 6 ] 3+ in dimethyl sulfoxide solution with WinXAS fitted model functions and separate scattering contributions and Fourier transforms with magnitudes and imaginary parts, Raman and IR spectra of deuterated dimethyl sulfoxide and of [Sc(OS(CD 3 ) 2 ) 6 ]I 3 . See http://www.rsc.org/suppdata/dt/b4/ b413486a/ structure of dimethyl sulfoxide (see Fig.…”

“…Relatively small shifts, decreasing the C-H stretching frequency less than 20 cm −1 , have been suggested to indicate weak hydrogen bonding. 3 However, careful interpretations are necessary when vibrational coupling may occur, for example band splitting due to Fermi resonance with overtones, 6 and for systems with long range electrostatic attractive forces. 7 In crystal structures geometry criteria based on the atomic arrangement are useful aids in attributing C-H · · · O interactions as actual hydrogen bonding.…”