Thermochemical study of adducts of tetramethylurea with zinc, cadmium, and mercury halides

Abstract

The adducts [Zn(tmu)₂X₂](X = Cl, Br, or I), [Cd(tmu)₂I₂], and [M(tmu)X₂](M = Cd or Hg and X = Cl or Br) have been characterized. The shift of the CO stretching vibration to low frequency indicated that tetramethylurea (tmu) is oxygen bonded to the metals. The standard enthalpy values (ΔH_R^⊖) for the reactions MX₂(s)+n tmu(I)→[M(tmu)_nX₂](s) were determined by means of solution calorimetry. The values of standard enthalpy of formation (ΔH_f^⊖) of the above adducts in kJ mol^–1 were: –1 006 (ZnCl₂), –926 (ZnBr₂), –844 (ZnI₂), –690 (CdCl₂), –602 (CdBr₂), –775 (Cdl₂), –515 (HgCl₂), and –454 (HgBr₂). The standard enthalpy of vaporization of tmu (ΔH_v^⊖= 51.12 ± 0.73 kJ mol^–1) was obtained from vapour-pressure measurements. The values of the standard enthalpy of the reactions: MX₂(s)+n tmu(g)→[M(tmu)_nX₂](s), MX₂(g)+n tmu(g)→[M(tmu)_nX₂](s), and MX₂(g)+n tmu(g)→[M(tmu)_nX₂](g) were also determined.