Atom-based thermochemistry: predictions of the sublimation enthalpies of group 12 chalcogenides and the formation enthalpies of their polonides.
Surprising and useful linear relationships between the atomization enthalpies of molecules and the cohesion enthalpies of crystals are found by shifting the thermochemical reference zero from elements to free atoms. Although the reference shift looks extremely simple, such atom-based thermochemistry (ABT) offers a direct way to calculate and predict the standard atomization enthalpy of molecules, Delta(at) H degrees(g), or solids, Delta(at) H degrees(s), with good accuracy (J. Am. Chem. Soc. 2008, 130, 5962-5973). It appears that referencing to atoms is able to provide a new unifying perspective. For group 12 metal chalcogenides, ME with M = Zn, Cd, Hg, E = O, S, Se, Te, Po, diabatic bond dissociation enthalpies, Dd298, with reference to the 1D2 state of the chalcogen atoms are mandated, in order to analyze the bond strengths properly (Mol. Phys. 2007, 105, 1139-1155). In this case, ABT implies a 2-fold reference shift (i) from formation enthalpies to atomization enthalpies and (ii) from standard atomization enthalpies to diabatic atomization enthalpies. An excellent linear relationship is found between the Dd298(ME) values and the corresponding diabatic atomization enthalpy of the solids, Delta(at) Hd(ME, s). The regression line is Delta(at) Hd(ME, s, calc) = 2.2717Dd298(ME) + 148.1 kJ mol-1 with the correlation coefficient R = 0.9996, the standard deviation (SD) = 4.2 kJ mol-1 and a mean unsigned deviation (MAD) = 3.7 kJ mol-1. Updated and corrected gas phase standard enthalpies of formation, Delta(f) H degrees(g), are presented for all 15 group 12 metal chalcogenides, and their lack of correlation with the formation enthalpies of the crystals, Delta(f) H degrees(s), is documented. The standard sublimation enthalpies, Delta(subl) H degrees, are reported for the first time. Recent accurate theoretical Dd298 values for the group 12 metal polonides, MPo, are taken to derive the first prediction for the standard atomization, formation, and sublimation enthalpies of their solids.
von Szentpály
László
L
Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany. lszentpaly@yahoo.com