Vibrational Spectroscopic and Computational Studies on Formamide Solutions of Alkali Metal Ions
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Vibrational Spectroscopic and Computational Studies on Formamide Solutions of Alkali Metal Ions Kazuhiko Ohashi1 · Nobutaka Hikiishi2 Received: 1 October 2019 / Accepted: 19 December 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Infrared (IR) spectra were measured for formamide (FA, HCONH2) solutions of Li(ClO4) and Na(ClO4). Both CN stretch and CO stretch bands of FA are observed to undergo upshifts in the presence of the metal ions. Quantum chemical calculations were performed for Li+(FA)n (n = 1–7) and Na+(FA)n (n = 1–8) complexes in order to model the metal ions in FA solutions. In previous Raman studies of the Li+ system, the so-called chelate configuration was assumed, in which the Li+ ion was put into the center of a ring FA dimer. However, the present calculations reveal that such a configuration is in conflict with the observed band shifts. The experimental IR spectra are reproduced by adopting appropriate isomers of L i+(FA)5 and Li+(FA)6 complexes, in which all FA molecules are coordinated + i+ ion and N H2 group are on the to Li via the O atom, with a configuration such that the L same side of the CO bond. These complexes, especially Li+(FA)6, are also successful in replicating characteristic features observed in the previous Raman spectra. Similarly, an O-bound isomer of Na+(FA)6 is consistent with the experimental IR and Raman spectra of the Na+ system. A strong coupling among the CO oscillators of FA molecules is shown to be responsible for the upshifts of the νCO modes despite the coordination via the O atom. Keywords Formamide · Li(I) · Na(I) · Coordination modes · Vibrational frequency shifts
1 Introduction Formamide (FA, HCONH2) has been used as a solvent for many ionic compounds which are poorly soluble in water [1, 2]. Meanwhile, FA has been of special interest as a model compound in biochemistry [3]. The FA molecule, as well as water, has an ability to solvate
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1095 3-019-00943-6) contains supplementary material, which is available to authorized users. * Kazuhiko Ohashi [email protected]‑univ.jp 1
Department of Chemistry, Faculty of Science, Kyushu University, Motooka, Fukuoka 819‑0395, Japan
2
Department of Chemistry, Graduate School of Science, Kyushu University, Motooka, Fukuoka 819‑0395, Japan
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Vol.:(0123456789)
Journal of Solution Chemistry
both cations and anions. Anions can bind to the H atom(s) of the N H2 group of FA, whereas cations can bind to either of the O atom, the N atom, or both of FA. A variety of experimental techniques have been applied for investigating coordination structures of metal ions in the solution phase [4]. For instance, the X-ray diffraction method has provided static structural information, which is believed to be one of the most reliable data. Ohtaki and Wada studied the structures of solvated Li+ and Cl− ions in FA by means of X-ray diffraction [5]. Meanwhile, vibrational spectroscopy h
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