Divalent halides

The dihalides of Si and Ge are polymeric solids that are relatively unimportant compared to those of Sn and Pb. The latter elements are metallic in character and have well-defined +2 oxidation states. Physical data for the divalent halides are shown in Table 11.1. The compounds of Si(II) are relatively unstable because the reaction... 

Lattice Energies (kcal/molb) op Divalent Halides... 

Divalent halides EX2 can be made as reactive gas-phase species, but only for Ge are stable... 

Up until the last 25 years, the known oxidation states for molecular rare earth compounds were those of the final colunrn of Table 1.1 not in parentheses. Thus, all rare earths form compounds in very stable -i-III state, three Sm, Eu, Yb give +II compounds and Ce, Pr, Tb have compounds in the +IV state. As shown by the data in parentheses in the final column of Table 1.1, new oxidation state molecular compounds have been a recent research highlight, " and the divalent state is now known for all rare earth elements except Pm. On the other hand, ionic divalent halides LnX (X=Cl, Br, I) have been known for elements (Ln=Nd, Dy, Tm) other than Ln= Sm, Eu, Yb for many years from the work of soUd state chemists. However, the diiodides, Lnl (Ln=La, Ce, Pr, Gd) do not contain Ln but Ln " and are to be formulated La (e )(T)j. They show metallic properties. ... 

Divalent halides are prepared by reduction of LnX3 with Ln metal or hydrogen, for example... 

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