Issue 43, 2020

Proton motion inside [(DMF)2H]2[W6Cl14]: structural, Raman and luminescence studies

Abstract

Protonation of DMF by (H7O3)2[W6Cl14] results in the appearance of strongly proton coupled [(DMF)2H]+ dimers. Such units are captured as the cationic part of [(DMF)2H]2[W6Cl14] (1). The proton behavior in such dimers was studied for the first time with single crystal X-ray diffraction (XRD) and 1H MAS NMR, Raman and photoluminescence (PL) spectroscopic techniques. The experimental data reveal the presence of two types of [(DMF)2H]+ dimers in 1 (cisoidal and transoidal, with respect to the mutual orientations of their C–O groups) which differ in terms of the degree to which they interact with the cluster anions as the temperature decreases. At room temperature all the O⋯O distances in the [(DMF)2H]+ dimers are very short (2.375 Å) and almost equal. 1H MAS NMR spectra show a resonance line at 18.7 ppm which is very close to that observed in sodium hydrogen maleate with a strong hydrogen bond belonging to a single-well potential of proton motion. The temperature decrease leads to the differentiation of [(DMF)2H]+ dimers due to the elongation of the O⋯O distance in one pair while keeping a practically constant O⋯O distance in the second pair. The analysis of the cation–anion interactions reveals a strong difference between these two types of dimers which results from the shifting of one DMF molecule toward a terminal Cl ligand of the cluster anion. The DFT calculations were used to show the difference in O⋯H+⋯O stretches for two different dimers. Moreover, we have found the PL of such dimeric units in the solid state. The temperature screening of the PL behavior demonstrates two types of luminescent centers at low temperatures which coalesce at 298 K. The proton motion in the hydrogen bond was studied using Raman spectroscopy, which was beneficial to monitor the complex behavior over a very broad temperature range from 5 to 298 K. According to the Raman data, we are dealing with a symmetric double-well potential for the hydrogen bond at room temperature, which becomes a broad single well potential below 110 K for the [(DMF)2H]+ cation with a longer O⋯O distance (the cisoidal isomer) and below 60 K for the [(DMF)2H]+ cation with a shorter O⋯O distance (the transoidal isomer).

Graphical abstract: Proton motion inside [(DMF)2H]2[W6Cl14]: structural, Raman and luminescence studies

Supplementary files

Article information

Article type
Paper
Submitted
05 Aug 2020
Accepted
07 Oct 2020
First published
07 Oct 2020

Phys. Chem. Chem. Phys., 2020,22, 25344-25352

Proton motion inside [(DMF)2H]2[W6Cl14]: structural, Raman and luminescence studies

B. A. Kolesov, A. V. Chupina, A. S. Berezin, N. B. Kompankov, P. A. Abramov and M. N. Sokolov, Phys. Chem. Chem. Phys., 2020, 22, 25344 DOI: 10.1039/D0CP04152A

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