Adducts of cyclic ureas with zinc halides - a thermochemical study

Adducts formed between ZnX2 (X = Cl, Br, I) and 2-imidazolidinone (ethylene urea, EU) or tetrahydro-2-pyrimidone (propyleneurea, PU) of the general for mula ZnX2.2L (L = Eu or PU) had the standard molar enthalpies determined th rough reaction-solution calorimetry at 298.15 K: ZnX2(cr) + 2L(cr) = ZnX2.2 L (cr); Delta(r)H(m)(0)/kJ mol(-1): ZnX2.2EU, -(46.03 +/- 0.72); -(45.35 +/ - 0.58) and -(59.20 +/- 0.83) for chloride, and iodide, and ZnX2.2PU, -(44. 26 +/- 2.63); -(37.75 +/- 1.83) and -(46.96 +/- 1.43) for the same sequence of halides. From these values, the standard molar enthalpies of the crysta lline adducts were calculated for both the series. The standard molar entha lpies of sublimation for EU and PU were calculated by means of differential scanning calorimetry to give 83.7 +/- 1.9 and 89.3 +/- 2.5 kJ mol(-1), res pectively. These values enabled the calculation of the corresponding standa rd molar enthalpies of adducts in the gaseous phase. From these latter enth alpic values, the mean zinc-oxygen bond enthalpies were determined as 139.4 +/- 2.2, 130.1 +/- 2.2, 131.4 +/- 2.2 and 141.3 +/- 3.2, 129.1 +/- 3,0, 12 8.2 +/- 3.0 kJ mol(-1) for EU and PU adducts, for the above sequence of hal ides, (C) 1999 Elsevier Science B.V. All rights reserved.