Infrared spectroscopic and computational studies on formamide solutions of Ca2+• Vibrational frequencies of formamide and modes of coordination to Ca2+

Infrared spectroscopy for formamide (FA) solutions of Ca(CIO4)(2) shows that both CN stretch (v(CN)) and CO stretch (v(CO)) bands of FA undergo upshifts in the presence of Ca2+. Modeling of Ca2+ in FA solutions is accomplished by quantum chemical calculations for Ca2+(FA)(n) (n = 1-8) complexes with Polarizable Continuum Model (PCM). The calculations indicate that bidentate Ca2+(FA)(4) complexes are not consistent with the observed upshift of the v(CN) band, although a bidentate coordination of four FA molecules via both O and N atoms was assumed in a previous study of the same system. The experimental results are reasonably reproduced by adopting Ca2+(FA)(7) and Ca2+(FA)(8) complexes with a monodentate coordination of all FA molecules via the O atom. A strong coupling among the CO oscillators is shown to be responsible for the upshifts of the v(CO) modes despite the O atom coordination. (C) 2018 Elsevier B.V. All rights reserved.