Germylenes triatomic

The stability of molecules depends in the first place on limiting conditions. Small, mostly triatomic silylenes and germylenes have been synthesized successfully at high temperatures and low pressures, 718). Their reactions can be studied by warming up the frozen cocondensates with an appropriate reactant, whereas their structures are determined by matrix techniques 17,18). In addition, reactions in the gas phase or electron diffraction are valuable tools for elucidating the structures and properties of these compounds. In synthetic chemistry, adequate precursors are often used to produce intermediates which spontaneously react with trapping reagents 7). The analysis of the products is then utilized to define more accurately the structure of the intermediate. 

III. ELECTRONIC TRANSITIONS IN TRIATOMIC AND TETRAATOMIC GERMYLENES, STANNYLENES AND PLUMBYLENES... 

Similarly to the case of the triatomic species (Section III), comparison of absorption maxima of stable germylenes, stannylenes and plumbylenes bearing the same substituents at different divalent atoms of the Group 14 elements (Table 4) does not reveal any... 

Frequencies assigned to the fundamental vibrations of the triatomic germylenes, stannylenes and plumbylenes are collected in Table 7 together with corresponding data on triatomic silylenes for comparison. The vibrational frequencies are sensitive to the environment of the molecule. Therefore, the most precise frequency values measured under each type of condition used (in the gas phase and in different low-temperature inert matrices) by different spectroscopic methods are shown in the table for each of the CAs. Nonfundamental frequencies of triatomic and observed frequencies of polyatomic germylenes, stannylenes and plumbylenes are listed in the text. 

Besides the triatomic CAs, the molecular structures have been determined experimentally for only labile silylidene and germylidene, as shown in Table 10. At the same time most of the stable CAs have been characterized by X-ray analysis or by electron diffraction. The available structural data for some stable germylenes, stannylenes and plumbylenes have partly been presented in Section IV. The comprehensive consideration of the geometries of stable CAs is beyond the scope of the present review. 

As may be seen from inspection of Eqs. (5) and (6) the two / A(amino)carbene analogues react differently with lCp(CO)2Fe]2. While only one germylene inserts into the iron-iron bond forming 12, two stannylene units are inserted to form 13. In the first case a triatomic heterometal cluster is obtained with an electron count similar to that in compounds 10 and 11 and in the second case (Eq. 6) a tetra-atomic Fe-Sn-Sn-Fe zigzag chain with point symmetry Cj is obtained with Sn-Fe distances of 2.605(2) A and a Sn-Sn bond length of 2.991(2) A the Fe-Sn-Sn angle is 117.9(1)°. In contrast to compound 9, the Sn-N distances are not shortened in 13 and are found to be almost equal to that in the free stannylene (13 Sn-N 2.099(2) A). 

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