Main group metals, sublimation

The product (with en = 1,2-ethanediamine chelated) can be isolated readily. The transition metal carbonyls are usually far more robust than those formed by main group elements for example H3B(CO) decomposes below room temperature, whereas Cr(CO)6 can be sublimed without decomposition. 

Values of the sublimation enthalpy of main group and transition metals are shown in Table 2.3 2... 

Sublimation enthalpies, energies of atoms in ideal kink positions and bond energies between the two nearest atoms, main group and transition metals ... 

M[N(SiR3)2] can then be purified—for the main group derivatives (for application in the synthesis of alkoxides, see Zn (Goel, 1990), Cd (Boulmaaz, 1992), Pb (Matched, 1990 Papiemik, 1989), Bi (Massiani, 1990 Goel, 1990))—by sublimation direct from the reaction mixture, after removal of the Et20 in vacuum, and—for the early transition metal con tounds (Cr(II), Mn(ll) (Horvath, 1979)), after the removal of ether—by the extraction from the residue with pentane or hexanes, separating LiCl by decantation. It should be mentioned that this approach is hardly practically applicable for the synthesis of the derivatives of late transition metals such as Co, Ni or Cu because of poor stability of their amide derivatives (Bryndza, 1988). 

In the case of other Group 6 metals, the polymerization of olefins has attracted little attention. Some molybdenum(VI) and tungsten(VI) complexes containing bulky imido- and alkoxo-ligands have been mainly used for metathesis reactions and the ring-opening metathesis polymerization (ROMP) of norbornene or related olefins [266-268]. Tris(butadiene) complexes of molybdenum ) and tungsten(O) are air-stable and sublimable above 100°C [269,270]. At elevated temperature, they showed catalytic activity for the polymerization of ethylene [271]. 

The hydroxides, MOH, are white crystalline solids soluble in water and alcohols. They sublime unchanged at 350-400°C and the vapors contain mainly dimers. There is great diversity in the structures of the solid hydroxides depending on the metal radii and orientation of the OH groups leading to H-bonds of different strengths. Depending upon the temperature of crystallization, for example, NaOH can have three different forms.14... 

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