Dynamic properties of the urea molecules in α,ω-dibromoalkane/urea inclusion compounds investigated by 2H NMR spectroscopy

Abstract

² H NMR spectroscopy has been used to investigate the dynamic properties of the urea molecules in Br(CH₂)_nBr/[²H₄]urea inclusion compounds (n= 7–10) and in pure crystalline [²H₄]urea. In the Br(CH₂)_nBr/urea inclusion compounds, the urea molecules form an extensively hydrogen-bonded host structure, which contains linear, parallel tunnels within which the Br(CH₂)_nBr guest molecules are located. The urea molecules undergo a two-site 180° jump motion about their CO axes, on the ²H NMR timescale, at temperatures greater than ca. 200 K for the Br(CH₂)_nBr/[²H₄]urea inclusion compounds and at temperatures greater than ca. 300 K for pure crystalline [²H₄]urea. Quantitative details relating to the dynamic properties of the urea molecules in these solids are presented.