ENTHALPY OF METAL-LIGAND INTERACTIONS IN SOME ADDUCTS ZNX(2)CENTER-DOT-2L (X=CL, BR, L=LIGAND WITH O OR N AS ELECTRON-DONOR ATOM)

The enthalpies of dissociation of Zn-Y bonds, (D) over bar(Zn-Y), in a dducts of the type ZnX(2).2L (X = Cl, Br; L = ligand with O or N as do nor atom) were previously estimated by means of the extrathermodynamic hypothesis. The present paper confirms these previous calculations by means of: (a) using a thermochemical cycle involving the dissolution of solid and gaseous zinc chloride in the ligands, i.e. N,N-dimethylac tamide (dma) and pyridine (py). For ZnCl2.2dma and ZnCl2.2py, the valu es of (D) over bar(ZnO) found were 147 +/- 15 and 156 +/- 15 kJ mol(-1 ), respectively. These values are comparable to those obtained previou sly: 139 +/- 15 and 153 +/- 15 kJ mol(-1), respectively. (b) Using the theory of Sanderson and the attribution of the bonding order leading to values of 146 +/- 15 and 141 +/- 15 kJ mol(-1) for the same adducts . For the adducts ZnCl2.2tppo and ZnBr2.2tppo (tppo = triphenylphosphi neoxide), the same value of 199 +/- 15 kJ mol-l was obtained for (D) o ver bar(ZnO), whereas for the adduct ZnCl2.2pyo (pyo = pyridine-N-oxid e) the (D) over bar(ZnO) value 230 +/- 15 kJ mol(-1) was found. The va lues previously reported for these tppo and pyo adducts were 184 +/- 1 5, 169 +/- 15 and 232 +/- 14 kJ mol(-1), respectively. By means of ano ther thermochemical cycle the enthalpy of sublimation of the adducts w as also estimated, with values close to those reported previously.