Appearance potential, calculating bond enthalpy from

It has been studied by IR spectroscopy (when trapped in a low-temperature matrix) and by mass spectrometric studies on the vapor. Isotopic studies ( Cl/ Cl and 0/ 0) allow the 0-P-Cl bond angle to be calculated from the IR spectra at ca. 105° (i.e. close to the bond angle of CH2PCI). From the observed appearance potential (20.9 eV) of P+ [AP(P+)j in the mass spectrum of OPCl, it is possible to estimate the enthalpy of atomization of OPCl(g) via the Bom Haber cycle (Scheme 6). Hence, since the standard enthalpies of formation of P(g), 0(g), and Cl(g) are all known, the standard enthalpy of formation of OPCl(g) [A // 9g(OPCl)] may be estimated as -250.7 kJmol . ... 

The choice of SbCls appears unfortunate for technical and theoretical reasons. From the experimental point of view, SbCls catalyses the reaction of chlorinated solvents with amines, which prevents the easy and accurate study of this very important class of nitrogen bases. In the same way, the frequently used solvent hexamethylphosphoric triamide does not give reliable results with SbCls. From the perspective of the theoretical prediction of DN, the 136 electrons of SbCls and the position of Sb in the fourth row of the periodic table make quantum chemical calculations on a series of SbCls complexes difficult. Semi-empirical PM3 calculations of complexation enthalpies have been performed [38] on SbCls complexes with 12 bases. At this low calculation level, only 43% of the variance of gas-phase calculated enthalpies is explained by experimental enthalpies in CH2CICH2CI. At the ab initio or DFT level, we are aware of only two studies the first [39] on five nitriles and pyridine and the second [40] on H2S complexes with SbCls. For the pyridine-SbCls complex, the gas-phase enthalpy, calculated without BSSE, is -115.5 kJ moF while the experimental value in CICH2CH2CI amounts to —142.3 kJ mol . It must be noted that antimony is described with the use of an effective core potential that incorporates major relativistic effects. In the end, the nature of the Sb—B dative bond does not seem to have been studied in depth and no theoretical prediction of the SbCls affinity can easily be made for Lewis bases. 

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