Stannylenes triatomic

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

Some numerical characteristics of the observed electronic transitions in triatomic germy-lenes, stannylenes and plumbylenes of the EX2 and EXY types are collected in Table 1 and Table 2, respectively. Similar data on the triatomic silylenes are included for comparison in these tables. Some molecular constants of germylidene and its silicon analog are compared in Table 3. 

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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