Solution chemistry compounds, enthalpy

The lanthanide and actinide halides remain an exceedingly active area of research since 1980 they have been cited in well over 2500 Chemical Abstracts references, with the majority relating to the lanthanides. Lanthanide and actinide halide chemistry has also been reviewed numerous times. The binary lanthanide chlorides, bromides, and iodides were reviewed in this series (Haschke 1979). In that review, which included trihalides (RX3), tetrahalides (RX4), and reduced halides (RX , n < 3), preparative procedures, structural interrelationships, and thermodynamic properties were discussed. Hydrated halides and mixed metal halides were discussed to a lesser extent. The synthesis of scandium, yttrium and the lanthanide trihalides, RX3, where X = F, Cl, Br, and I, with emphasis on the halide hydrates, solution chemistry, and aspects related to enthalpies of solution, were reviewed by Burgess and Kijowski (1981). The binary lanthanide fluorides and mixed fluoride systems, AF — RF3 and AFj — RF3, where A represents the group 1 and group 2 cations, were reviewed in a subsequent Handbook (Greis and Haschke 1982). That review emphasized the close relationship of the structures of these compounds to that of fluorite. 

Samarium has two common oxidation states +2 and -h3. Upon solution in toluene under nitrogen, an anionic Sm(II) species, [(—CH2—)5]4-calix-tetrapyrrole Sm(THF)[Li (THF)]2[Li(THF)2]Cl, forms, in part, the compound [(—CH2—)5]4-calix-tetrapyrrole Sm(THF)Li2[Li(THF)](/r -OCH=CH2) . However, this compound is a lithium enolate derived by elimination of THF. In that the metalloorganic reagent is rather similar to what will be discussed in Section XI as part of vanadium enolate chemistry, we fail to understand why in the former case with Sm a lithium enolate is formed but in the latter with V it is an ynolate that is produced. Almost nothing is known to allow comparing the energetics of metal enolates and related ynolates. We note from the enthalpies of... 

In some cases experimental values of A,//°and AA are available, but in general these data are calculated using experimental or estimated values of the standard enthalpies of formation, AfH°, and entropies, S°, of all species involved in the reaction. It should also be pointed out that most organometallic reactions of interest occur in solution at temperatures not far from ambient, and that under these conditions the enthalpy term in Equation (6) is often dominant. Therefore, thermodynamic stability trends of organometallic compounds can frequently be analyzed solely in terms of A H°. When necessary, however, computational chemistry calculations or simple estimation schemes can normally be used to predict A, ° with an acceptable accuracy. " ... 

---