Group IVA hydrides

The properties of the nonstoichiometric hydrides are discussed in groups the saline hydrides, the Group IVA hydrides, the rare earth hydrides, the actinide hydrides, the Group VA hydrides, and palladium hydride. 

The cubic phase in each of the Group IVA hydrides has the fluorite structure, so that the hydrides should have the stoichiometric formula, MH2, when all the normal lattice positions are occupied. However, these structures become unstable before reaching the stoichiometric composition, and undergo a phase transition to a tetragonal structure. The room temperature homogeneity ranges of these hydrides are shown in Table II. Titanium hydride also forms a tetragonal phase... 

Nash, C.S., Bursten, B.E. Spin-orbit, VSEPR theory, and the electronic structure of heavy and superheavy group IVA hydrides and group VIIIA tetrafluorides. A partial role reversal for elements 114 and 118. J. Phys. Chem. A 103, 402-410 (1999)... 

FIGURE 6.8 Boiling points of hydrides of groups IVA,VA, VIA, and VIIA. 

These examples all involve group IVa metal complexes, suggesting that the desired behavior might be possibly an attribute of early transition metal hydride complexes, an area that has been studied considerably less than complexes of metals that are further to the right of the early transition metals on the periodic table. Indeed, as discussed in this volume (see Chapter 10), a zirconium hydride complex recently has been found to reduce CO to methanol among other products. 

However, for catalytic reduction of CO, there is one additional problem the products of CO reduction (alcohols or water) react readily with these strongly hydridic group IVa complexes. This would lead to self-destruction of the catalyst after a single cycle. Hence a third criterion must be added ... 

Reaction with Further Electrophiles of Group IVA (Sl,Ge,Sn). IV-Silylated aziridines can be prepared from ethyleneimine by amination of chlorosilanes in the presence of an HC1 acceptor, by dehydrocondensation with an organosilicon hydride or by cleavage of a silicon—carbon bond in 2-furyl-, 2-thienyl-, benzyl-, or allylsilanes in the presence of an alkali metal catalyst (262—266). N-Silylated aziridines can react with carboxylic anhydrides to give acylated aziridines, eg, A/-acetylaziridine [460-07-1] in high yields (267). At high temperatures, A/-silylaziridines can be dimerized to piperazines (268). Aldehydes can be inserted... 

Various experiments have suggested that, in general, hydride derivatives of the group IVA metals show considerable hydridic character as Thus compounds such as (CpzTiHz) and Cp TiBH4 react... 

A number of examples of insertion of CO2, CS2, and COS into transition metal hydride bonds have been reported. Well-defined reactions from groups IVA or VA are... 

Separations of hydrides of silicon and germanium have been achieved by GC on ester and silicone phases. Separation of alkyltin mono- and dihydrides by GC requires the use of most inert stationary phases to preclude on-column reaction. Among the Group IVA elements, lead alone has hydrides for which GC has not proved possible. 

Hydride addition reactions are utilized to synthesize a number of group IVA-containing polymers ... 

Hydride generation in AAS became popular after 1970 in response to a study by Holak, which demonstrated the analytical potential of this approach for arsenic. Since then, elements of groups IVA, VA, and VIA of the periodic table have been shown to form volatile covalent hydrogen compounds with sufficient efficiency to be of practical analytical use. These include arsenic, bismuth, germanium, lead, antimony, selenium, tin, tellurium, and to some extent, indium and thallium. 

We now turn to a discussion of calculations on systems that have served as test molecules for relativistic methods. We describe the hydrides of gold and platinum and the hydrides of the main group IVA elements as representative cases. 

Table 4 X—H Bond Lengths (A) in Hydrides of Main Group IVA Calculated with Relativistic Corrections and by Experiment...

Metal hydrides of Groups 13 (IIIA) and 14 (IVA) of the periodic table (e.g., AIH3, GaH3) as well as many of their alkyl and aryl derivatives (e.g., R2AIH, Ar3SnH) add... 

You can see the effect of hydrogen bonding clearly in the boiling point data of the binary hydrides of Groups 14 to 17 (IVA to VIIA), shown in Figure 4.16. In Group 14, the trend in boiling point is as expected. 

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