Calcium, strontium and barium

   The heavier group 2 metals are highly electropositive, and metal–ligand bonding is generally considered to be predominantly ionic. Nonetheless, this remains a topic for debate and theoretical investigation. While Cp₂Be and Cp₂Mg are monomeric and are soluble in hydrocarbon solvents, Cp₂Ca, Cp₂Sr and Cp₂Ba are polymeric and are insoluble in ethers and hydrocarbons. Increasing the steric demands of the substituents on the C₅-rings leads to structural changes in the solid state and to changes in solution properties, e.g. (C₅Me₅)₂Ba is polymeric, {1,2,4- (SiMe₃)₃C₅H₂}₂Ba is dimeric and (ⁱPr₅C₅)₂Ba is monomeric. Oligomeric metallocene derivatives of Ca²⁺‏, Sr²⁺‏ and Ba^2+‏ typically exhibit bent C₅^_M^_C₅ units, but in (ⁱPr₅C₅)₂Ba, the C₅-rings are coparallel. The iPr₅C₅-rings are very bulky, and sandwich the Ba^2‏+ ion protectively, making (ⁱPr₅C₅)₂Ba airstable.

Fig. 1.1 Part of a chain in the polymeric structure (X-ray diffraction 118 K) of (η⁵-C₅Me₅)₂Ba illustrating the bent metallocene units [R.A. Williams et al. (1988) J. Chem. Soc., Chem Commun., p. 1045]. Hydrogen atoms have been omitted; colour code: Ba, orange; C, grey.

   The 1990s saw significant development of the organometallic chemistry of the heavier group 2 metals, with one driving force being the search for precursors for use in chemical vapour deposition. Some representative synthetic methodologies are given in equations 1.1–1.4, where M= Ca, Sr or Ba.

                                    (1.1)

                                 (1.2)

             (1.3)

       (1.4)

مواضيع ذات صلة

كيمياء القصدير

تطبيقات الطبقات الثنائية الهيدروكسيد

تطبيقات عملية التبادل الأيوني

مواد التبادل الأيوني Ion exchanger

ظاهرة التبادل الايوني Ion Exchange

تاريخ التبادل الايوني Ion Exchange History

كيمياء البلاتين ومعقداته

كيمياء البلاديوم ومعقداته

طرائق تقدير النحاس

كيمياء النحاس ومعقداته

طرائق تقدير النيكل

كيمياء النيكل ومعقداته