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Solvation structure of magnesium, zinc, and alkaline earth metal ions in N , N ‐dimethylformamide, N , N ‐dimethylacetamide, and their mixtures studied by means of Raman spectroscopy and DFT calculations—Ionic size and electronic effects on steric congestion
Author(s) -
Asada Mitsunori,
Fujimori Takao,
Fujii Kenta,
Kanzaki Ryo,
Umebayashi Yasuhiro,
Ishiguro Shinichi
Publication year - 2007
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1662
Subject(s) - solvation , chemistry , ionic radius , inorganic chemistry , steric effects , metal ions in aqueous solution , solvation shell , magnesium , raman spectroscopy , coordination number , coordination sphere , zinc , alkaline earth metal , ion , metal , crystallography , stereochemistry , organic chemistry , physics , optics
The solvation structure of magnesium, zinc(II), and alkaline earth metal ions in N , N ‐dimethylformamide (DMF) and N , N ‐dimethylacetamide (DMA), and their mixtures has been studied by means of Raman spectroscopy and DFT calculations. The solvation number is revealed to be 6, 7, 8, and 8 for Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ , respectively, in both DMF and DMA. The δ ( O CN) vibration of DMF shifts to a higher wavenumber upon binding to the metal ions and the shift Δν(= ν bound − ν free ) becomes larger, when the ionic radius of the metal ion becomes smaller. The ν (NCH 3 ) vibration of DMA also shifts to a higher wavenumber upon binding to the metal ions. However, the shift Δν saturates for small ions, as well as the transition‐metal (II) ions, implying that steric congestion among solvent molecules takes place in the coordination sphere. It is also indicated that, despite the magnesium ion having practically the same ionic radius as the zinc(II) ion of six‐coordination, their solvation numbers in DMA are significantly different. DFT calculations for these metalsolvate clusters of varying solvation numbers revealed that not only solvent–solvent interaction through space but also the bonding nature of the metal ion plays an essential role in the steric congestion. The individual solvation number and the Raman shift Δν in DMF–DMA mixtures indicate that steric congestion is significant for the magnesium ion, but not appreciable for calcium, strontium, and barium ions, despite the solvation number of these metal ions being large. Copyright © 2006 John Wiley & Sons, Ltd.