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

Abstract Infrared spectroscopy for formamide (FA) solutions of Ca(ClO 4 ) 2 shows that both CN stretch ( ν CN ) and CO stretch ( ν CO ) bands of FA undergo upshifts in the presence of Ca 2+ . Modeling of Ca 2+ in FA solutions is accomplished by quantum chemical calculations for Ca 2+ (FA) n ( n  = 1–8) complexes with Polarizable Continuum Model (PCM). The calculations indicate that bidentate Ca 2+ (FA) 4 complexes are not consistent with the observed upshift of the ν 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 Ca 2+ (FA) 7 and Ca 2+ (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 ν CO modes despite the O atom coordination.