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.