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

Abstract

The adducts Zn(mu)2X2 (X = Cl, Br), M(mu)X, (M = Cd, Hg and X = Cl, Br) have been characterized. The CO and NH stretching frequencies indicate that methylurea (mu) is bound to metals through oxygen. Enthalpies of dissolution of the adducts in ethanol or methanol have been measured calorimetrically. Combination with the enthalpies of solution of metal halides and ligand in the same solvents at 298.15 K yielded the standard enthalpy [Formula: see text] for the reaction: MX,(s) + nmu(s) → M(mu)nX2, (s): Zn(mu)2Cl2, (−36.27±0.51); Zn(mu)2Br2, (−37.52±0.97); Cd(mu)Cl2, (−22.78±0.26); Cd(mu)Br2, (−9.58±0.26); Hg(mu)Cl2, (−13.91±0.41);and Hg(mu)Br2,(−13.29±0.48). The standard enthalpies of formation of the adducts in the same sequence as above, [Formula: see text] (s, 298.15 K): −1024, −938, −701, −612, −524, and −470 kJ mol−1, were determined from these values, the standard enthalpy of the ligand (−285 ± 15 kJ mol−1) being obtained via combustion calorimetry, and literature values of the standard enthalpies of metal halides being used. With the determination of the standard enthalpy of sublimation of the ligand (78.2 kJ mol−1) it was possible to determine the standard enthalpies of the reactions MX2(g) + nmu(g) → M(mu)X2 (s) and M(mu)nX2 (s) → MX2 (s) + nmu(g). The enthalpies of metal–oxygen bonds were also estimated.