Individual solvation number of first-row transition metal(II) ions in solvent mixtures of N,N-dimethylformamide and N,N-dimethylacetamide—Solvation steric effect

摘要: Raman spectra of solutions manganese(II), nickel(II), copper(II) and zinc(II) perchlorate with varying molality were measured in N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) their mixtures by titration spectroscopy at 298 K. The in-plane OC–N bending vibration 660 cm−1 DMF the stretching N–CH3 740 DMA show an appreciable shift to a higher frequency upon coordination solvent molecules metal ion. These deconvoluted bound bands (νbound) ion extracted from free band (νfree). number or individual solvation n mixture, i.e., nDMF nDMA for DMA, respectively, evaluated analyzing intensity decrease increasing It turned out that manganese(II) is six-coordinated over whole composition range mixtures, nDMF + nDMA = 6, relationship nDMF/nDMA = xDMF/xDMA, where x denotes mole fraction solvent, holds mixture. With regard ion, total decreases 6 xDMA mixtures. In neat two are extracted, indicating species, Zn(DMA)62+ Zn(DMA)42+, coexist equilibrium. six-coordinate solvated nDMF/nDMA > xDMF/xDMA This shows steric effect operates unlike one. six-coordinated, although structure strongly distorted owing Jahn–Teller effect. Indeed, ascribable solvents equatorial axial positions extracted. position, among molecules, while nDMF/nDMA ⩽ xDMF/xDMA position. expected because Cu–O(solvent) bond length longer electron-pair donating ability slightly stronger DMA. magnitude Δν (=νbound − νfree) depends on Δν values vary according Δν = (ar)−n, function ionic radius r parameters evaluated. implies M–O(DMF) M(DMF)6−n(DMA)n2+ elongated